Date: Sat, 30 Mar 1996 08:44:25 From: JRaerocad@gnn.com (Jeff Russell) Subject: Re: (2)Micro in load-bearing layups? George Graham answered: > >How can this leaching through be avoided, short of allowing full >drying of the micro layer first?? > >I've been anxious to spread the best building hint I know. > >There is a method of making perfect cores, which gives perfect >layups without the bleed through of the micro. It is callled "Hard >shelling". AeroCad writes: Ditto on that. Our testing on peel strenght was also better doing this >Essentially, you do let the micro slurry cure before laying on the >glass. First, mix your epoxy, then add a small amount of denatured >alchohol, then mix in the micro balloons. The alcohol lets you add much >more micro. Cover the foam with a light layer, cure and sand to perfection. >Repeat as required until the shape is as good as you can get it. Your slurry can also be a dry micro mix to fill wire-lag or burn outs and mis-bonding. >Then you lay up the cloth with straight epoxy. The micro sands >easily and is still much stonger than the foam alone. The bond between >the glass and the sanded micro surface is as strong or stronger than >the wet method. > >I use West epoxy for this step. We use Alpha Epoxy to also do this. >Another hint, as soon as the epoxy starts to set up (knife trim >time) if you are certain that the layup is perfect, apply a light coat of >dry micro to fill the cloth weave, in those areas where you know >you won't need to bond to (use peel ply on those). After cure,a light >sanding of the micro should make the part ready for paint, or >perhaps just more micro in any low spots. This avoids sanding into the > cloth. No itching, no weakening the part. Don't forget the FAA requirement for precover inspections. If you micro your part on the outside to cover the skins this could become a problem if your inspector can not see what they need?? >The parts will actually end up stronger and lighter, and it is much >less nasty work, and quicker overall. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Sat, 30 Mar 1996 07:46:22 -0500 (EST) From: "George A. Graham" Subject: Re: Micro in load-bearing layups? On Sat 30 Mar 1996, George Graham answered: > How can this leaching through be avoided, short of allowing full drying > of the micro layer first?? > >I've been anxious to spread the best building hint I know. There is a method of making perfect cores, which gives perfect layups without the bleed through of the micro. It is callled "Hard shelling". Essentially, you do let the micro slurry cure before laying on the glass. First, mix your epoxy, then add a small amount of denatured alchohol, then mix in the micro balloons. The alcohol lets you add much more micro. Cover the foam with a light layer, cure and sand to perfection. Repeat as required until the shape is as good as you can get it. Then you lay up the cloth with straight epoxy. The mico sands easily and is still much stonger than the foam alone. The bond between the glass and the sanded micro surface is as strong or stronger than the wet method. I use West epoxy for this step. I learned this half way through my project, and only wish I'd known it earlier. Another hint, as soon as the epoxy starts to set up (knife trim time) if you are certain that the layup is perfect, apply a light coat of dry micro to fill the cloth weave, in those areas where you know you won't need to bond to (use peel ply on those). After cure,a light sanding of the micro should make the part ready for paint, or perhaps just more micro in any low spots. This avoids sanding into the cloth. No itching, no weakening the part. The parts will actually end up stronger and lighter, and it is much less nasty work, and quicker overall. From: George Graham 209 Euclid Ave. Kenmore, NY 14217 (716) 874-3277 ca266@freenet.buffalo.edu Date: Sat, 30 Mar 1996 10:56:26 -0500 From: JHocut@aol.com Subject: Re: "Hard Shell" Layups This method sounds intriuging, especially for myself as I am usually flying solo while doing big layups and am really pushed to get everything done before the epoxy gets too thick to work with. At first, it would seem like this would result in both heavier and weaker layups. A couple of questions: 1. How much is a "small amount" of alcohol. If I've got, say, 100 gm of epoxy, are we talking 1 cc, a teaspoon, a gallon? (Obviously I'll never be able to cook 'cause I don't know what a "smidgin" is.) I'm also a little concerned about adding alcohol to my epoxy, I'll have to try this on some scraps and see it for myself before I do it on the plane. 2. Jeff Russell indicated that he saw better peel strengths this way than with conventional layups. I wonder if Jeff could share some numbers with us. I'd also be real interested in seeing the weight comparison. Like I said, this sounds real interesting. It might really save me some grief since I'm one that can't leave well enough alone and always end up sanding the foam too far trying to achieve perfection. Thanks, Jim Hocut jhocut@aol.com Date: Sat, 30 Mar 1996 11:34:03 -0500 From: Phillip.Johnson@Lockheed.on.ca (Phillip Johnson) Subject: Re: "Hard Shell" Layups The hard shell process realy works. I've been doing this for several years and it allows one to do large layups solo. One of the real benifits is that you can apply the resin through several layers of glass. When I made my wings I spent a week of evenings doing the hard shell for two wings and getting them just perfect. In the region over the spar caps I added flox (no alcohol) rather than micro for the obvious reasons. I used about 10% to 20% alcohol, I guess, for my micro. It becomes obvious when you are mixing. If there is too much alcohol then the mix quickly drys when you apply it and it becomes difficult to apply but even in this state it is stronger than the foam. Basically the more alcohol you use the more micro you can add to the mix which means a lighter structure and its easier to sand. Once you have your hard shell and you are sattisfied, then lay your first layer of UNI in the appropriare position and tape the ends to a firm point. Since the tape can be difficult to remove from the glass I always give myself adequate margin for taping.Now bring your second piece of UNI up to butt with the first and tape the ends in a simmilar fashion. You will notice the the UNI nearly always wants to separate from the first so I use a needle and a light cotton thread to do a running stitch holding the two pieces together. You repeat this until the surface is covered, then, and this is the good bit, You repeat the process for the second ply with the fibres running in the appropriate direction. Once you are satisfied that every thing is good clean and flat you have a choice: 1) go to bed and get a good nights sleep, or 2) start the layou now. which ever you chose it does not matter. Now start your layup from one end, moving down the wing. If you want to use peel ply, apply it in stages as you are going down the wing. Since you are only moving in one direction there should be no need to re-visit any spot so you are always dealing with fresh resin thus a lighter structure. Using this process there is no rush because you are never having to re-visit old work and part cured resin. The standard method requires that you do and that's where the trouble begins. When I did my wings I was a coward because of Nat's comments in the plans so Nigel Field helped me. We did the layup for one side of two wings in 3 hours, 1.5 hours each. Phillip Johnson Date: Sun, 31 Mar 1996 16:49:04 From: JRaerocad@gnn.com (Jeff Russell) Subject: Re: "Hard Shell" Layups Jim Hocut writes: >Jeff Russell indicated that he saw better peel strengths this way than >with conventional layups. I wonder if Jeff could share some numbers >with us. I'd also be real interested in seeing the weight comparison. AeroCad writes: 1) Peel strength is normally going to be as good as the tear strength of the foam. We did not find a better peel strength of foam, but of glass. The thicker the glass, the harder the peel. If dry micro is under the glass as a thin skin, its will act like a thicker skin. As long as no contaminates are not left between the cured micro and new skin, a good peel strength should be found. 2) Fill is fill, when it comes to weight. The better the job you do on cutting your cores and core prep will determine a percentage of outcome on weight. 3) I feel that peel ply should be used carefully. If more resin is added to the peel ply to fill the weave, you just added more weight to your part. (Best Way) If you are using it to lay the fibers down (flatten) without adding resin. Be careful not to wick out to much resin or the glass will show dry. (not wetout properly) (1) We use it under glass on top the foam where a glass to glass bond will someday go. (2) To cover a tape glass joint. I add more resin here for a good transition. (3) For Vacuum bagging. Anywhere else seems to me a waste of time and good money. Hope this helps. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Subject: Re: "Hard Shell" Layups Date: Mon, 1 Apr 1996 09:02:35 -0500 (EST) From: "Randy Smith" > Once you have your hard shell and you are sattisfied, then lay your > first layer of UNI in the appropriare position and tape the ends to a > firm point. Since the tape can be difficult to remove from the glass I > always give myself adequate margin for taping.Now bring your second > piece of UNI up to butt with the first and tape the ends in a simmilar > fashion. You will notice the the UNI nearly always wants to separate > from the first so I use a needle and a light cotton thread to do a > running stitch holding the two pieces together. You repeat this until > the surface is covered, then, and this is the good bit, You repeat the > process for the second ply with the fibres running in the appropriate Does this mean tape (as in duct tape) the overhang to some other surface? This is so the glass won't move while you "wing walk :-)" down the part with the epoxy? I get the mental image of cutting all the cloth at once and having it all layed out on the part one on top of the other all taped down with the running stitch. All that is missing is the epoxy at this point? I want to be sure since I've never heard of doing it this way. > direction. Once you are satisfied that every thing is good clean and > flat you have a choice: > > 1) go to bed and get a good nights sleep, or > 2) start the layou now. > > which ever you chose it does not matter. Now start your layup from one > end, moving down the wing. If you want to use peel ply, apply it in I'm asuming that we now start the epoxy application to the layup? > stages as you are going down the wing. Since you are only moving in > one direction there should be no need to re-visit any spot so you are > always dealing with fresh resin thus a lighter structure. How do you ensure that there are no dry spots? Do you pour on lots (ie more than you normally would) of epoxy and work it down the part using rollers/squeegees/etc? This may all be obvious to others, but I have never worked with or seen the epoxy/cloth combination to understand how it wets out. This seems like it would work well. > Phillip Johnson > -Randy Smith --* --- -* **-* *-** -*-- -* Crash Rescue Team 7 - Don't PANIC! |Cozy MkIV| NCR General Purpose Computing Randy.Smith@ColumbiaSC.NCR.COM |---( )---| Global Support Center Voice 803-939-7648, V+ 633-7648 ___o/o\o___ West Columbia, SC 29170 "I am the way, the truth, and the life..." -JC Date: Mon, 1 Apr 1996 12:02:59 -0500 From: Phillip.Johnson@Lockheed.on.ca (Phillip Johnson) Subject: Re: "Hard Shell" Layups Randy Smith Writes: > Does this mean tape (as in duct tape) the overhang to some other > surface? Yes I use Masking tape but duct tape is OK. Do the trimming while you go. > This is so the glass won't move while you "wing walk :-)" down the > part with the epoxy? I get the mental image of cutting all the > cloth at once and having it all layed out on the part one on top of > the other all taped down with the running stitch. All that is > missing is the epoxy at this point? I want to be sure since I've > never heard of doing it this way. You've got it. > I'm assuming that we now start the epoxy application to the lay-up? yes. > How do you ensure that there are no dry spots? Do you pour on lots > (ie more than you normally would) of epoxy and work it down the > part using rollers/squeegees/etc? This may all be obvious to > others, but I have never worked with or seen the epoxy/cloth > combination to understand how it wets out. This seems like it > would work well. I'm still using Safe-T-Poxy II so the colour allows you to see the air bubbles, but yes You pour more epoxy than a single layer. You actually find that you use less epoxy than doing it in two separate layers. Phillip Johnson Date: Mon, 1 Apr 1996 13:29:20 -0500 From: JHocut@aol.com Subject: Re: "Hard Shell" Layups This is fantastic! I just had to go out and try as soon as I heard about it (why didn't someone tell me about this sooner?) I can now fully understand how the finished part is lighter - by adding a small amount of alcohol to the resin it is able to pull MUCH more micro into the "slurry", resulting in a much lighter filler than the driest dry micro you get with straight resin. I wasn't satisfied 'till I experimented with this a little bit, and was really surprised at what I learned. I started out by adding about 20% (by wt) of denatured alcohol to my resin, then made dry micro as usual. By the time you get a good dry micro, you've already achieved a much lighter mixture than you've ever seen before. But wait, it gets better. Add just a touch more alcohol, mix it in, and the mixture is fairly wet again, ready to take more micro. Add micro again 'till it's good and dry, then add a touch more alcohol to make it wet again, ready to take more micro. I kept this up 'till I had a mixture the consistency of shaving cream, only it was much lighter than shaving cream. I stopped here, but probably could have kept right on adding alcohol and micro. Obviously the point would be reached where the strength of the resulting material would be unacceptable. When applying this material, if it starts to stiffen up just add a touch of alcohol and it will come back around (within a reasonable time period of course). After a days' cure, the material was readily sandable. And, like someone already pointed out, it might not be as strong as a wet micro slurry, but it's still a heck of a lot stronger than the foam beneath it. A couple of questions: 1) Would this type of material be suitable for final finishing over glass (especially in regards to impact resistance)? 2) In regards to final finishing, does West or Alphapoxy have any advantage over 2427 (besides the fact that Alphapoxy costs a little less)? Thanks, Jim Hocut jhocut@aol.com Date: Mon, 01 Apr 1996 18:21:42 -0500 From: Nigel Field Subject: Hard Shelling Folks, I have found the hardshell method to be excellent and have always employed it since Ive been building. I first used it 20 years ago when building glass RC models. Gordon and Phil neglected to mention that I was the one who introduced it to them and others. Following are some additional pointers: a) Use only Methyl Alcohol, its sold at hardware stores as Methyl Hydrate as it contains very little water. Isopropyl(medical rubbing alcohol) or Ethyl alcohols (booze) contain lots of water are not good. b) The maximum practical alcohol percentage is about 20% for the micro to retain strength. Any more makes it too soft and harder to apply as it tends to clump up. In the thicker micro layers used to fill voids, the alcohol will slow the cure by up to three times depending on the percentage used. Allow it to fully cure before attempting any finish prime as it will probably interact with the alcohol which is still boiling off. c) The micro "prime" or hard shell has to be cured before any glass is applied. What this does is make the micro resin proof (like water proof) so when you do your layup over it it wont soak up any more epoxy, unlike the conventional wet micro layup method which will, no matter how dry you make your fill coat, it will just fully saturate with epoxy and get heavy. It also allows easy sanding and leveling of the part before glass work, an important advantage. d) The final micro fill should be done with pure epoxy only in order to achieve a tougher harder finish. Soft micro will dent and chip off more easily. The weight difference is negligible if you used the method in c) above. e) Laying out all of the cloth layers before any epoxy, as described by Phil allows you to get the fibres perfectly aligned and dead straight as called out in the plans. It also makes 1 person large layups dead easy. I defy anyone to do this alone using the conventional wet core method. f) Try a brush instead of a squegee, with a litle practice it is easy to get just the right amount of epoxy, no silvery areas or bubbles but no shiny wet areas. It will take a minute or so to soak through the layers, be patient. A hair dryer helps a lot if its cool. If you must use a squegee try a dry wall scraper, they come in different widths and flexibility, just knock the sharp corners off with a file first. They work better than anything else I have found. Good for micro too. Dont over do it or you will end up distorting the weave and it will pull a bunch of air into the layup. This may not be apparent until about an hour after its done, then by magic a bunch of air pockets will suddenly appear and you have to go over it again with a brush. Allow one hour to inspect before you go to bed. g) If your hardner gets old and turns dark and thick, dont pitch it, just stirr in a little alcohol until its back to normal. CAUTION******** This will probably degrade the resin strength somewhat, although the tests I have done did not show any change over fresh hardner ONCE FULLY CURED. Cure times are increased however with the alcohol. *******DO NOT use this mix for thicker critical areas like SPARS as the alcohol may not all get out and a weaker layup could result. Its fine for cowlings, consols and other less critical thin sections. Try a test yourself on a sample. I reasoned that if it did increase final strength or made no change, then Hexcel would have included it in the blend to make it wet out better. Regarding Triax cloth, if you examine a piece closely you will find lots of space between the fibre tows, much more than UNI. These act like a sponge and soak up LOTS of resin. Repeat my test in laying up two identical samples, one of triax and one three plies UNI and then weigh and test them to destruction. See what you get. IMO triax only saves time, and if you use the dry layup method above it saves nothing. The only place you could use it is on the wing top which call for three plies but the weave orientation will not be the same as Rutan called for so the tortional properties will differ. The bottom skin is two plies so triax just adds lots more weight for nothing. Don't use it, its arguably weaker and heavier than 3 plies of UNI. Hope this helps someone, Nigel Field Date: Mon, 01 Apr 96 19:06:44 est From: "Larry Schuler" Subject: Re: "Hard Shell" Layups Jim Hocut wrote: > I stopped here, but probably >could have kept right on adding alcohol and micro. Obviously the >point would be reached where the strength of the resulting material >would be unacceptable. >When applying this material, if it starts to stiffen up just add a touch >of alcohol and it will come back around (within a reasonable time period >of course). After a days' cure, the material was readily sandable. And, >like someone already pointed out, it might not be as strong as a wet micro >slurry, but it's still a heck of a lot stronger than the foam beneath it. Jim, I think we would all like to know how you tested the revised peel strength with a glass layup over the hard shell, or???. Any one else done any testing? If so describe test and results. {please} This is exciting; and I haven't even opened a can of epoxy yet!!! Larry Schuler MKIV-#500 Date: Tue, 02 Apr 1996 16:56:47 From: JRaerocad@gnn.com (Jeff Russell) Subject: Re: "Hard Shell" Layups Jim Hocut writes: >I think we would all like to know how you tested the revised peel >strength with a glass layup over the hard shell, or???. > >So far I have only tested physical properties of the material >itself, not peel strength. >( It was Jeff Russell, I believe, who had said he did peel >strength testing). >I employed several very exacting test methods, using highly >calibrated equipment: Our testing was about in the same manner >The stuff is a whole lot stronger than the foam beneath it, and you >can't separate it from the foam without bringing up a big glob of >foam with it, so basically it's strong enough. The only >thing left then is how well glass adheres. >I had asked a similar question of Jeff Russell about his peel strength >testing, it's plenty good enough, at least as strong as the conventional >method. Ditto on that. Micro surry should almost always be stronger then the foam (even 18 lb last-a-foam) BE CAREFUL USING ALCOHOL !!!!! This is like using a solvent with epoxies. If you get any solvents that have epoxy resins mixed in it on your bare skin, your asking to have skin problems very quickly down the road. Never clean your brushes or tools without good solvent proof gloves. Vinegar also works good to soak and clean tools in (no solvents). I am sure the airborne problem becomes worse with alcohol off gassing. So use lung protection. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Tue, 2 Apr 1996 14:48:52 -0500 From: JHocut@aol.com Subject: Re: "Hard Shell" Layups >I think we would all like to know how you tested the revised peel strength > with a glass layup over the hard shell, or???. So far I have only tested physical properties of the material itself, not peel strength. ( It was Jeff Russell, I believe, who had said he did peel strength testing). I employed several very exacting test methods, using highly calibrated equipment: 1. The fingernail test. How easy is it to plunge a fingernail exactly 1.63 mm into the material in question? Result - the "hard shell" material was much stronger than H45 PVC foam, Urethane foam, and 4.5# Last-A-Foam. 2. The table-knife test. How easy is it to scrape material away from the surface of the material in question using a standard table knife at a 43 deg. angle with 27.5 pounds of force applied. Result - the "hard shell" material was much stronger than H45 PVC foam, Urethane foam, and 4.5# Last-A-Foam. 3. The hammer test. How easy is it to dent the material in question with a standard framing hammer that is dropped from 0.97 meters. Result - the "hard shell" material was much stronger than H45 PVC foam, Urethane foam, and 4.5# Last-A-Foam. Do you see what I'm getting at here? The stuff is a whole lot stronger than the foam beneath it, and you can't separate it from the foam without bringing up a big glob of foam with it, so basically it's strong enough. The only thing left then is how well glass adheres. I had asked a similar question of Jeff Russell about his peel strength testing, and while I don't remember exactly what his reply was, I think the gist of it was in line with my experiences regarding physical strength - it's plenty good enough, at least as strong as the conventional method. Jim Hocut jhocut@aol.com Date: Tue, 02 Apr 96 18:08:12 est From: "Larry Schuler" Subject: Re: "Hard Shell" Layups Jim Hocut wrote: {a GOOD disertation on hard shell strength}. Thanks for the info Jim. I figured it was stronger than the foam; and you gave some examples. A mix of glass bubbles and Elmer's glue might be too; but that wouldn't necessarily mean it's a good idea. I was more concerned about the peel strength with the glass application. I just keep thinking about Mr. Whitman's "delamination" and would prefer not to have the same experience after flying for several years. I realize this is glass and he used fabric; but the potential "delamination" is similar. Don't get me wrong, I REALLY like the idea of the hard shell from what I have been reading here. I haven't quite started building yet, and am just trying to go about this in an educated manner. If someone has done some testing, it would be nice to know how, and the results. Maybe others will benefit too. Perhaps Jeff or someone else can fill in the details...... Larry Schuler MKIV-#500 From: "Volk, Ray" Subject: Re "Hard Shell" layups Date: Tue, 02 Apr 96 15:55:00 PST Phillip writes; >You repeat the process for the second ply with the fibres running in the appropriate > direction. This technique sounds like a great idea, especially for those of us who are doing layups solo, and the clock keeps on ticking. I have one concern through, and that is when you do a layup the old fashion way, you wet out, and squeegee in the direction of the fibers starting from the center, pulling out all waves and wrinkles such that all fibers end up perfectly straight and in tension (sounds like a little wishful thinking). Sort of like combing wet hair. If you lay a second layer of different orientation on top of the first layer, how do you make sure there are no wrinkles and waves in the under layer since you cannot see it or squeegee it? I guess the obvious answer is to go around the outside and tug all strands but it seems like your working partially blinded. Ray Volk rvolk@space.honeywell.com Cozy #426 Date: Wed, 3 Apr 1996 06:46:31 -0500 (EST) From: "George A. Graham" Subject: hard shelling Reply to: Larry Schuler, See Oct 93 Central States newsletter for tests and comments or, open the can and test it yourself. I tried the multi layer layup, and was not satisfied. Chasing the air bubbles out drove me nuts. I'd rather stick to one ply at a time. From: George Graham 209 Euclid Ave. Kenmore, NY 14217 (716) 874-3277 ca266@freenet.buffalo.edu Date: Fri, 5 Apr 1996 00:30:31 -0500 From: StetsonE@aol.com Subject: Hard Shelling - Opposing View Wow. Alot of knowledeable people are all for this hard shelling idea, and several of these folks have much more composite experience than I have. Because of this, I'm a little reluctant to give an opposing view for fear of getting hammered, but I'm going to anyway. My Long-EZ structure is complete and finished through primer. I've spent most of the past 12 months in the finishing stage, and I believe that ANY technique that requires you to do more micro sanding than is absolutely necessary should be avoided. You'll have plenty of opportunity in the latter stages of your project to build muscles. No use starting early! Any way you cut it, micro is much harder to sand than foam. If you're goal is the perfect foam core, then hotwire your cores a little oversize and then sand them down to the proper contour. That way you're sanding foam (easy), not micro (much harder). I did this on my winglets and was pleased with the result. I built hotwire templates 1/8" oversize all around, then used the plans templates as sanding templates. Worked great. Get a friend to help sand the cores so the talking numbers can be followed at each end of the core. The sanding only took 15 minutes per winglet side. Don't think that, either with hardshelling or sanding cores to shape, your resulting "perfect" cores will require no more than filling the weave during finishing. Not so! You still have to use a heavy dose of micro in some areas, like wing to strake transition, and the wing to winglet joint. The winglet attach layups are nearly 1/8" thick, and to properly fair them into the rest of the wing and winglet requires substantial micro fill. On my wings I started this transition on the wing approx 5 feet from the winglet to provide for an invisible transition. If you want to hardshell because you want enhanced peel strength, my thought is why? Existing peel strength is more than adequate for flight loads, as demonstrated by the 1000's of canard types currently flying. We haven't seen any inflight failures attributable to skin delamination. True, many planes have localized delams, probably because of people walking on their wings (I've seen it!), using inadequate wing stands when changing tires, dropping tools on the wings, setting the gear with a shoulder, etc, etc. The answer is not to do these things. Set the gear by grabbing onto the lower winglet, not under the wing. As Rutan says, treat your skins like eggshells. Maybe you work alone and think that hardshelling is a good way to prep for a one person layup. May be true, but think of all the extra micro sanding you must do just to prep for the layup. The alternative is to do the layup the plans way, and NOT work alone for the large layups. When I layed up my wings, I got two extra people to help. The three of us positioned the glass, then one mixed and the other two squeeged epoxy. With the shop at 80 degrees and using SafeT-Poxy II, each wing surface layup took no more than 5 hours, start to finish. In my estimation, hardshelling a wing surface will take at least an hour to apply the micro(alone), a day to cure, 4 hours to sand down(alone), and maybe another 6 hours to do the layup (alone, start to finish). And with either technique, you will STILL have to do micro sanding during the finishing stage. I think the math speaks for itself. The answer is to make at least 10 friends. You'll need that many, because I've found that I can con them into helping the first time because they don't know what they're getting into. Getting them to help a second time is much, much more difficult! I'll admit that my comments are based on only my experience, and I have never tried hardshelling. I welcome further edification. Stet Elliott stetsone@aol.com Perpetual Long-EZ builder Date: Fri, 5 Apr 1996 06:45:56 -0500 (EST) From: "George A. Graham" Subject: Re: Hard Shelling - Opposing View On Fri, 5 Apr 1996 StetsonE@aol.com wrote: > > I'll admit that my comments are based on only my experience, and I have never > tried hardshelling. I welcome further edification. > > Stet Elliott > stetsone@aol.com > Perpetual Long-EZ builder > Dear Stet, Thank you for your perspective. I have tried it and love it. It may be more work, but the parts turn out better. I learned this from Nigel Field, if you could see how beautiful his work is, you too would be willing to try it. George Graham ca266@freenet.buffalo.edu Date: Sat, 06 Apr 1996 16:33:25 -0500 From: Nigel Field Subject: Re: Hard Shelling - Opposing View At 12:30 AM 4/5/96 -0500, Stet Elliott wrote: Stet makes some very good points. >My Long-EZ structure is complete and finished through primer. I've spent >most of the past 12 months in the finishing stage, and I believe that ANY >technique that requires you to do more micro sanding than is absolutely >necessary should be avoided. You'll have plenty of opportunity in the latter >stages of your project to build muscles. No use starting early! >Any way you cut it, micro is much harder to sand than foam. I completely agree with you on this. The final finish takes a lot of work, and hard shelling the cores may even add some time overall. The chief advantages of hardshell are the weight savings, and ease of applying the glass without anyone else, plus nice straight fibres over a true core. The softer micro sands very easily. I use a hardboard spine with a 40 grit sanding belt contact cemented to it. You dont need a fine finish just flat. The weight advantage is significant on the open cell foams such as divinycell which take a lot of micro to fill. With the wet method a lot of that fill is epoxy. Its not so bad on the Styrofoam as it has smaller cells but over the total area of a wing it can add up. I haven't done any measurements on this, but I know how much micro I used, it was a lot, and any method to decrease the epoxy ratio helps save weight. >Get a friend to help sand the cores so the talking numbers can be followed at each end of the >core. The sanding only took 15 minutes per winglet side. >Don't think that, either with hardshelling or sanding cores to shape, your >resulting "perfect" cores will require no more than filling the weave during >finishing. Not so! You still have to use a heavy dose of micro in some >areas, like wing to strake transition, and the wing to winglet joint. The >winglet attach layups are nearly 1/8" thick, and to properly fair them into >the rest of the wing and winglet requires substantial micro fill. On my >wings I started this transition on the wing approx 5 feet from the winglet to >provide for an invisible transition. Again I fully agree, the overlap transitions have always bugged me for this reason. I thought about releiving the foam on my cores to allow for this but the spar is in the way so its hard micro for me too. > >If you want to hardshell because you want enhanced peel strength, my thought >is why? Existing peel strength is more than adequate for flight loads, as >demonstrated by the 1000's of canard types currently flying. I dont think hardshell will increase peel strength, that was never intended as one of the advantages, but it is stronger than the foam by quite a bit so the foam will peel before the micro. >We haven't seen any inflight failures attributable to skin delamination. True, many planes >have localized delams, probably because of people walking on their wings >(I've seen it!), using inadequate wing stands when changing tires, dropping >tools on the wings, setting the gear with a shoulder, etc, etc. The answer >is not to do these things. Set the gear by grabbing onto the lower winglet, >not under the wing. As Rutan says, treat your skins like eggshells. Once again no argument. I have never seen a delam near the winglets on any LE VE, there is a bunch of plies in that area to hold it on so its pretty solid. The only delam I got on my VE was on the canard LE about 3 wide 4" deep after a bird strike at 160 KTS. I could not see it but could hear it by tapping with a small screwdriver. I drilled two small holes in the skin and injected pure epoxy. After cure it sounded solid again. >Maybe you work alone and think that hardshelling is a good way to prep for a >one person layup. May be true, but think of all the extra micro sanding you >must do just to prep for the layup. The alternative is to do the layup the >plans way, and NOT work alone for the large layups. When I layed up my >wings, I got two extra people to help. The three of us positioned the glass, >then one mixed and the other two squeeged epoxy. With the shop at 80 degrees >and using SafeT-Poxy II, each wing surface layup took no more than 5 hours, >start to finish. In my estimation, hardshelling a wing surface will take at >least an hour to apply the micro(alone), a day to cure, 4 hours to sand >down(alone), and maybe another 6 hours to do the layup (alone, start to >finish). And with either technique, you will STILL have to do micro sanding >during the finishing stage. I think the math speaks for itself. The answer >is to make at least 10 friends. You'll need that many, because I've found >that I can con them into helping the first time because they don't know what >they're getting into. Getting them to help a second time is much, much more >difficult! I know, been there, done that. Hard to find someone close who I would let work on my project. The other builders near me are metal bashers and Phil J. is 1 hour away with his own project to do. Got my wife to help once, but only once :-). This is another big reason for me to use the dry layup method. I much prefer to work alone anyway and this allows me that freedom. > >I'll admit that my comments are based on only my experience, and I have never >tried hardshelling. I welcome further edification. I dont think there is much more to say about it. Its lighter no question, easier by yourself and there is perhaps a bit of an ego thing in displaying perfect glass structures with no dips or joggles prior to the final fill. Its just another way to skin the cat. Nigel Field Date: Mon, 8 Apr 1996 19:11:43 -0400 From: Fritzx2@aol.com Subject: Re: Hard Shelling - Opposing View Nigel Field wrote in a response to Steve Elliot: >I dont think hardshell will increase peel strength, that was never intended >as one of the advantages, but it is stronger than the foam by quite a bit so >the foam will peel before the micro. I, independently, hard shelled before I knew there was such a thing. I'll explain. After all the bulkheads were mated to the sides but before the center keel was installed, I became increasingly uneasy with the few dry spots and the not-so-straight weave on the back of the front seat. (Lesson #1: If you have any doubt that you need to repair something, do it right away because it only gets harder, more work, to do later). Back to my point. I elected to sand the back of the front seat to roughen up the 1 ply of BID to reglass. After a lot of work I was finished repairing the back of the seat....or so I thought. I then installed the center keel and one night I cut the center rectangle out of the front seat to gain access to the chart pocket in the center keel. After examining this "core sample" I became very bummed. I now had a core of .75" PVC foam that was micro'ed and glassed the traditional way on the one side and essentially hard shelled on the other side since I had sanded all the 1 layer of BID off to do the repair. On the hard shell side of the core, I'll admit that the peel stength between the micro and the foam was mutch stronger than the foam itself. BUT, the peel strength between the hard shell and the 1 layer of BID was nearly non-existant! The sawing motion that removed the core delaminated the hard shell side but did not delaminate the "traditional method" layup side. I had sanded with a 36 grit sandpaper before replacing the 1 ply BID on the back side of the seat. To repair the seat the second time, I peeled the entire 1 ply of BID from the hard shell and all the hard shell remained on the foam. Clearly here, the weakest link was the bond between the glass and the hard shell. After this unplanned "test" I became very skeptical of any processes that resulted in a hard shell surface prior to the first layup. I did not do any further investigation into why the hard shell method did not result in a good interlaminate bond between the hard shell and the glass, and cannot explain why or if this was an isolated occurance. I would, however, recommend that the total system: foam-to-micro and micro-to- glass peel strength be verified before relying on this method. The concern I have is the strength between the hard shell and the glass. Someone might have posted the results of testing the peel strength of the glass-to-hard shell but I can't remember. Contrary to popular opinion, this is what happened to me and I would feel remiss if I didn't share it with the group. Does anyone have any comments? John Fritz Fritzx2@aol.com Date: Mon, 08 Apr 96 19:46:06 est From: "Larry Schuler" Subject: Re[2]: Hard Shelling - Opposing View John, Thanks for this opinion. I have asked about the glass to hard shell strength before and only seemed to get general answeres. I am curious though....... Did you change resin systems between? Could the area have become contaminated some how? Was the repair layer fully cured when you ripped it off? The hard shell you describe wasn't the micro/epoxy/alcahol mix that is currently being discussed; makes me wonder about laminating over ANY cured epoxy!! What on earth made you grab hold of the repair glass and try to rip it off anyway???? {Don't get me wrong, I'm glad you did; and you probably are too.} How did you end up repairing the seat back if glass/epoxy wouldn't stick to it? Did I read this right? Larry Schuler MKIV-#500 ______________________________ Reply Separator _________________________________ Subject: Re: Hard Shelling - Opposing View Author: Fritzx2@aol.com at INTERNET Date: 4/8/96 6:18 PM Nigel Field wrote in a response to Steve Elliot: >I dont think hardshell will increase peel strength, that was never intended >as one of the advantages, but it is stronger than the foam by quite a bit so >the foam will peel before the micro. I, independently, hard shelled before I knew there was such a thing. I'll explain. After all the bulkheads were mated to the sides but before the center keel was installed, I became increasingly uneasy with the few dry spots and the not-so-straight weave on the back of the front seat. (Lesson #1: If you have any doubt that you need to repair something, do it right away because it only gets harder, more work, to do later). Back to my point. I elected to sand the back of the front seat to roughen up the 1 ply of BID to reglass. After a lot of work I was finished repairing the back of the seat....or so I thought. I then installed the center keel and one night I cut the center rectangle out of the front seat to gain access to the chart pocket in the center keel. After examining this "core sample" I became very bummed. I now had a core of .75" PVC foam that was micro'ed and glassed the traditional way on the one side and essentially hard shelled on the other side since I had sanded all the 1 layer of BID off to do the repair. On the hard shell side of the core, I'll admit that the peel stength between the micro and the foam was mutch stronger than the foam itself. BUT, the peel strength between the hard shell and the 1 layer of BID was nearly non-existant! The sawing motion that removed the core delaminated the hard shell side but did not delaminate the "traditional method" layup side. I had sanded with a 36 grit sandpaper before replacing the 1 ply BID on the back side of the seat. To repair the seat the second time, I peeled the entire 1 ply of BID from the hard shell and all the hard shell remained on the foam. Clearly here, the weakest link was the bond between the glass and the hard shell. After this unplanned "test" I became very skeptical of any processes that resulted in a hard shell surface prior to the first layup. I did not do any further investigation into why the hard shell method did not result in a good interlaminate bond between the hard shell and the glass, and cannot explain why or if this was an isolated occurance. I would, however, recommend that the total system: foam-to-micro and micro-to- glass peel strength be verified before relying on this method. The concern I have is the strength between the hard shell and the glass. Someone might have posted the results of testing the peel strength of the glass-to-hard shell but I can't remember. Contrary to popular opinion, this is what happened to me and I would feel remiss if I didn't share it with the group. Does anyone have any comments? John Fritz Fritzx2@aol.com Date: Mon, 08 Apr 1996 21:54:10 -0400 From: Nigel Field Subject: Re: Hard Shelling - Delam At 07:11 PM 4/8/96 -0400, John Fritz Fritzx2@aol.com wrote: >I, independently, hard shelled before I knew there was such a thing. Deletions............ >On the hard shell side of the core, I'll admit that the peel stength between >the >micro and the foam was mutch stronger than the foam itself. BUT, the peel >strength between the hard shell and the 1 layer of BID was nearly >non-existant! >The sawing motion that removed the core delaminated the hard shell side but >did not delaminate the "traditional method" layup side. I had sanded with a >36 >grit sandpaper before replacing the 1 ply BID on the back side of the seat. >To repair the seat the second time, I peeled the entire 1 ply of BID from the >hard >shell and all the hard shell remained on the foam. Clearly here, the weakest >link was the bond between the glass and the hard shell. John this is of considerable concern. Can't explain why the glass failed to bond to the cured micro especially since you had sanded it. I have never experienced such a problem and have ripped apart my share of goofs also. Its always the micro/foam junction that lets go with a thin layer of foam staying with the micro. This (I assume) was pure epoxy micro with no alcohol thinner so it seems that it just would not bond to the cured micro for some reason. Perhaps the type of Resin is a factor? There have been some reports of poor bonds with the amine catalyst resins, think Marc Z. had this problem due to the amine blush, but then you sanded it first??? I have used 2184/2410 since it came out and the original Safety Poxy 1 before that, so don't have much experience with amine epoxy systems. I did have a problem about 5 months ago when I laid up the LE on my ailerons using 7781 9oz glass. After cure I started to remove the peel ply and the glass came off just about as easily. I pulled it all off in one piece without difficulty. I had used new hardner, the same stuff that I had also made my spar caps from, so I was pretty unhappy. Called Phil J. and told him since he got the same hardner. He suggested some tests using 7781 and regular 7725 BID which I did on a scrap piece of cured layup. It was lightly sanded and cleaned with alcohol first then the two strips layed on with a tab left to pull. After two days RT cure I pulled off the 7781 just like peel ply but could not remove the 7725 the tab let go first. Examination of the delam showed an epoxy layer bonded to the old glass with the weave pattern of the 7781 showing just like you get with peel ply. Seems the problem was with the glass itself but I don't know why, so I dont use it anymore. I will do some more testing on this subject and report. I have some Aeropoxy 2032/3417 which is an amine system so will try that too. If anyone else has had some similar experience I would very much like to hear about it. Nigel Field Date: Mon, 8 Apr 1996 22:21:11 -0400 From: Fritzx2@aol.com Subject: Re: Re[2]: Hard Shelling - Opposing View In a message Larry Schuler responded to my message: >John, Thanks for this opinion. I have asked about the glass to hard shell > strength before and only seemed to get general answeres. That's all I recall. > I am curious though....... Did you change resin systems between? Could >the area have become contaminated some how? I did not change epoxy type nor was the area contaminated. If anything, for my first layups, which was either the back or front side of the front seat, the foam, glass and work area were probably overly clean. > Was the repair layer fully cured when you ripped it off? Yes, it had cured for weeks while I made, fitted, and installed my entire front air duct/center keel assembly complete with fuel selector bracket. > The hard shell you describe wasn't the micro/epoxy/alcahol mix that is > currently being discussed; True >... makes me wonder about laminating over ANYcured >epoxy!! For me anyhow, I am removing any "hard shell" areas incidentally resulting from joining foam pieces before I do any subsequent layups. For me it's worth the extra work in light of my experiences on the back of the the front seat. > What on earth made you grab hold of the repair glass and try to rip it >off anyway???? {Don't get me wrong, I'm glad you did; and you probably >are too.} When I examined the "core sample" taken out of the front seat to open up the front seat to the chart pocket in the center keel, I noticed the difference between the hard shell method that I stumbled into when compared to the traditional method of layups on the opposite sides of the core/front seat. The 1 ply BID layup over the hard shell side of the seat (which was the result of sanding the previosly existing 1 ply bid in order to make my repair) delaminated VERY easily from the underlying hard shell surface. On the other side of the core, the traditional method of microing and glassing all in one step was still firmly attached to the foam. > How did you end up repairing the seat back if glass/epoxy wouldn't stick >to it? > Larry Schuler > MKIV-#500 After removing the glass (rather easily), I meticulously removed the micro hard shell from the foam with a very sharp wood chissel and then started over by sanding it smooth, microing, and glassing in one step. John Fritz Fritz@aol.com From: Lee Devlin Subject: Hard shelling Date: Tue, 9 Apr 96 0:20:20 MDT In reading over the postings on delamination related to hard shelling, it occurred to me that glassing directly to foam with micro is structurally different than allowing the hardshell to cure and then applying the glass. In the case of applying the micro and glass simultaneously, you have a chemical bond all the way from the glass to the foam. The foam has pores which soak up epoxy and provide adhesion all the way from the foam to the glass with a chemical bond due to cross-linking of the epoxy and a mechanical bond due to the pores in the foam. When hardshelling, there will not be a chemical bond all the way from foam to glass as the cross-linking is already complete in the hardened micro. Therefore, the peel strength has to come from mechanical adhesion of the glass/epoxy to the sanded micro surface. Sand as you may, it will only provide scratches with minor undercuts to which the epoxy must adhere. This is not necessarily a serious issue in every composite structure as the core material is typically in compression, but in those areas where delamination is a concern (or dis-bonding as Rutan refers to it), it could present structural problems. Delamination is the separation of two or more glass plies from each other, dis-bonding is the separation of the glass from the core material. Lee Devlin Date: Tue, 9 Apr 1996 10:49:04 -0400 From: Fritzx2@aol.com Subject: Re: Hard Shelling - Opposing View In a message Jeff Russell wrote: >John, > >What kind of resin was used?? Hexcel 2427 Nigel Field wrote: > much stuff deleted >There have been some reports of poor bonds with the >amine catalyst resins, think Marc Z. had this problem due to the amine >blush, but then you sanded it first??? I did indeed sand it first plus I would like to add that since I live in the south (read that high humidity) I purchased a dehumidifier and consider the the control of humidity in the work area just as important as the temperature. John Fritz Fritzx2@aol.com Date: Thu, 18 Apr 1996 13:34:00 -0400 From: Dick.Finn@FNB.sprint.com Subject: Hard Shell Hello everyone, I realize we have pretty much beat the topic of hard shelling to death with a stick, however...... I felt some concern/interest in the method. My fear was that it could result in the skin peeling off of the hard shell as there would only be a mechanical bond. Even so, there are many examples in the construction where the plans call for laying up over cured glass. Some of these are in what I would consider critical structural areas. Most notably, the wing skin is laid up over a cured spar cap which is in turn laid up over a cured sheer web. Laying up glass over cured glass is certainly different then laying up glass over cured micro , however, there is still a simil arity. Any wa y, I decided to run an experiment. My approach follows. 1. I cut two 2' long by 2" wide strips of styrofoam about 1" thick. 2. The two strips were microed side by side onto a scrap piece of parti cle board. 3. After the micro had cured I applied a relatively stiff mixture of micro to one of the strips. I squeegeed it in and applied peel ply to assure a relatively smooth surface. 4. After cure I removed the peel ply and sanded the hard shell piece with coarse sand paper to provide a mechanical bond. I vacumned both strips and noted that there were a number of pin holed in the hard shell. 5. I mixed a thin micro and applied it to the non-hard shell strip of foam. This micro was squeegeed in. 6. I painted the hard shell with a thin layer of epoxy. I noted that this made the pin holes stand out. 7. I then laid up a single layer of bid covering both strips. 8. After allowing the pieces to cure 24 hours I intended to peel back the edge and clamp a piece of safety wire to the bid. I was going to loop the wire over a piece of conduit in the ceiling and slowly attach weights to see how much it took to peel the glass off. Things didn't work out as planned. When I peeled back the edge it seemed to come off with only a pound or two of pull. My first thought was that this hard shell method wasn't working too well. When I looked at my labels, however, I realized I was pulling on the standard lay-up. I tried pulling up the hard shell lay-up and it also detached with only a few pounds pull also. I examined the underside of the lay-up and found that both were pulling the foam up. I was able to see no difference on the amount of foam attached to either lay-up (it was a very thin layer). The hard shell lay-up did not detach at the micro layer. Even though someone else had reported this result, I was surprised. I fully expected the mechanical bond to separate easily. There is still some question in my mind as to what will happen to the mechanical bond after several hundred hours of in-flight flexing. In any case, this is what I found. I have decided on how I am going to proceed and pass on the results of my mildly scientific study to all of you for your amusement and edification. Hard shelling is not called for in the plans and I firmly believe that any deviation from the plans commits the builder to running his own set of tests as appropriate to the changes made. In other words, don't make a decision based on my comments and blame me if you fall out of the sky. Dick Finn Cozy Mark IV #46 DICK.FINN@FNB.SPRINT.COM Date: Fri, 19 Apr 1996 07:47:54 -0400 (EDT) From: Randy Crutfield Subject: Re: Hard Shell Hey guys, I got on board when this discussion was already in progress, and have had a thought in my mind the whole time regarding this issue. If this is what spurred the original discussion , please forgive me. In chapter &, page 4, at the end of the first paragraph (Step 3), Nat says; "Sand the foam surfaces with 120 grit to smooth any roughness, vacuum, and squeegee micro on the foam before glassing. If already microed, and smooth, vacuum and paint with epoxy before laying down the cloth." Take a look at this, I don't believe that I am reading it out of context, or quoting it out of context. This would seem to indicate that "hard-shelling" is okay, at least for the bottom of the fuselage. Randy Date: Fri, 19 Apr 1996 09:16:42 -0400 (EDT) From: Randy Crutfield Subject: Re: Hard Shell Sorry, My last message should have read chapter 7, page 4...etc, instead of Chapter 8. Randy Date: Wed, 24 Apr 1996 16:42:00 -0400 From: Dick.Finn@FNB.sprint.com Subject: Hard Shelling - Delam A week or so ago I published a report of my hard shell delamination experiment. Last night I was cleaning up the work area and before throwing the experiment away I ripped the glass all the way off of the hard shell and standard layup. While things were generally as I reported earlier, last night I noted that in several small areas (1/4" to 3/8" in size) around the edges of the layup the glass delaminated from the micro when using the hard shell method. This did not occur in the standard layup. I apologise for the ommision on the original report. You can draw your own conclusions from the above. I strongly advise testing it yourself before using the hard shell method. Dick Finn Cozy Mark IV #46 DICK.FINN@FNB.SPRINT.COM From: Marc J. Zeitlin Subject: COZY: Hard Shelling Redux Date: Tue, 25 Jun 96 8:44:09 EDT People; A few months ago we had a discussion regarding "Hard Shelling" foam prior to layups, and the concomitant useage of alcohol in the micro to thin it and allow the use of more glass bubbles. I thought I'd give an update on my experiences with it. I tried hard shelling while glassing the exterior of the nose (chapter 13). I found that trying to hard shell over the urethane foam was very difficult, due to the crumbly nature of the urethane. I had a hard time keeping the foam from disintegrating under the sanding of the cured micro, as well as trying to get the urethane to absorb the relatively dry mixture. However, I just tried hard shelling again on the hot-wired PVC foam cores for the winglets (both top and bottom), and am VERY pleased with the results. The PVC (due to it's larger pore structure) absorbs much more micro than the urethane does, so there's a larger potential for weight savings. Also, since there's more micro and the foam is more structural, I've been able to get a very nice, smooth finish on the cores with minimal tearout of the foam (even with 36 grit sandpaper). As others have previously recommended, I've been mixing my micro up into a very thick slurry - essentially wet micro - and then adding about 25% - 33% as much alcohol as I had epoxy. This thins it down just about to the consistancy of pure epoxy. I then add more glass bubbles until it's like thin shaving cream; maybe 75% more bubbles than before (it's essentially like being able to easily squeeqee very dry micro into the foam). At any rate, the winglet cores are starting to look very nice - I think this technique will really work well on the PVC foam layups (winglets, wings, strakes, etc.) to get a smooth substrate for the glass, and will minimize later filling and sanding. Thanks to those who recommended and explained this technique. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: 26 Jun 96 12:16:32 EDT From: "William E. Buckley" <74744.2301@compuserve.com> Subject: COZY: Winglet Cores I hate to do it, but I must make a correction to Marc Z's posting about hard shelling his winglet cores. Two or three times he called them PVC. They're not PVC, they're stryrofoam. We never hot-wire cut PVC. William E. Buckley (Cozy Mk IV, #437, Chap. 9) 74744.2301@compuserve.com From: UYFA59A@prodigy.com ( JAMES J CULLEN IV) Date: Tue, 17 Sep 1996 13:53:08, -0500 Date: 17 Sep 96 Subject: COZY: Hardshelling -- Caution -- A Long Article. -- [ From: James J. Cullen, Ph.D. * EMC.Ver #2.5.1 ] -- While Nat Puffer's recent article about hardshelling in the October, 1996 Cozy Builder's Newsletter was timely (I'm hardshelling a wing core) , I have to take strong exception to Nat's opinions. In the Fall of 1993, I conducted a series of experiments to determine the effects of hardshelling on peel strength. The results were published in the October, 1993 issue of the newsletter of the Central States Association (Volume 32). For those without access to the issue, the article is reproduced, without photographs and with more current comments in brackets, below. Further discussion follows the article. Hardshelling Jim Cullen (NV) -- Let's begin by acknowledging that I am not an expert in composite structures. I am a geologist by trade who happens to be two years [now 5] into the construction of a Cozy Mark IV. I was lurking on the computer network Internet about four months ago when I ran across a discussion group on experimental aircraft (rec.aviation. homebuilt). Some memos had been exchanged on the topic of hardshelling. The concensus was that hardshelling is something that one should never do because it results in a structure that is more prone to delamination than one built with normal techniques. Having never heard the term before, I continued to read... Hardshelling is performed by spreading micro slurry and/or dry micro over a foam core, and allowing it to cure, prior to laying up any fiberglass. The micro is contoured to shape and only after this has been done is the glass lay-up performed. (On wings, spars, and canards, micro is ***never*** spread between the spar caps and the outer skin). The logic seems to be that tighter dimensional tolerances can be maintained when contouring the micro -- the hard shell, if you will -- than can be achieved by contouring bare foam; this is especially true if the foam core is produced with a hot wire saw. The result is a finished airfoil that requires less filling. More importantly, there are fewer dips in the fiberglass skin, resulting in straighter glass strands and a stronger structure. The discussion on Internet revolved around delamination. Would a skin laid up over a hard shell delaminate more easily than one laid up in the normal manner? The author thought that it would. He had performed some experiments and found that the skin basically just popped off the underlying dry micro. This gave me pause for concern. The bottom half of my canard and the bottom half of my fuselage had been hardshelled before I had even heard of the term. Should I scrap my work? I called Nat Puffer -- the designer of the Cozy -- to discuss the problem. Basically, he could see no advantage to the technique, as long as the core had been properly shaped and prepared, and he agreed that hardshelling might result in a higher potential for delamination. He told me not to scrap my work, but advised me to be a bit more careful in hot wiring my cores and to be a little less zealous in sanding them -- good advice for everyone. Two weeks later, I discussed the problem with some builders at Burt Rutan's 50th birthday party in Mojave. The concensus seemed to be that hardshelling was a perfectly acceptable technique! One owner of a yellow California-based Long-EZ confessed that he had built his entire airplane that way. He thought that, at one time, Burt Rutan had advised against the technique but now thought it to be the technique of choice. Confusion appeared to reign among the experts, so I decided to do a little of my own testing. Figure 1 shows the basic test setup. A piece of blue polystyrene foam [measuring about 18" square] left over from my canard was divided into 4 sections [longitudinally, with a marking pen]. Section 1 was left bare for a normal layup, Section 2 with covered with micro slurry and Sections 3 and 4 were covered with a 1/16-inch thick layer of dry micro over micro slurry. In this manner, the piece was allowed to cure. After cure (Figure 2), Section 2 was sanded with 40 grit sandpaper. The dry micro was sanded off Section 3, and the dry micro was roughed up but not sanded off Section 4. The piece was vacuumed, painted with Saf-T- Poxy II, and a normal 2-ply BID lay-up was performed (Figure 3). Then, the layup was numbered and cut into 7 sets of test coupons (Figure 4). Sets 1 and 2 were peeled by hand, to obtain a qualitative feeling for potential delamination problems (Figure 5). The results, shown in Figure 6, were as follows: Section 1 -- the normal lay-up -- delaminated at the foam-glass interface with virtually no micro slurry remaining on the foam. The glass bent slightly as it was peeled back. Small pieces of foam (1/32" or less in size) adhered to the glass. Just about every builder has tried this at one time or another; nothing out of the ordinary occurred. Section 2 -- glass laid up over cured [and sanded] micro slurry -- exhibited precisely the same delamination pattern. No discernible difference in the amount of force required to perform the delamination could be detected. Section 3 -- glass laid up over the area where the dry micro had been sanded down to the level of the micro slurry -- also delaminated in the same way. Again, no noticeable difference in force was required to delaminate the structure. Section 4 -- glass laid up over 1/16" dry micro -- took considerably more force to delaminate. The dry micro adhered to the glass and delamination took place at the foam/micro slurry interface [the shell did not fail!]. The glass piece was noticeably stiffer -- to the point that the glass actually cracked, rather than being bent, as it was being peeled off the foam. >From this admittedly qualitative experiment, I would have to conclude that, if anything, hardshelling results in a structure that is stronger, more resistant to delamination, and possibly stiffer than one performed using conventional lay-up techniques. However, as I stated earlier, I'm not an expert in these matters. This article was written to foster discussion and bring out knowledge and experiences of other CSA members. So please write and tell us what you know. [No one ever did!] Also, if anyone has the proper facilities to measure the peel strength of my test coupons quantitatively and would like to perform some tests, the unused portions are available upon request [rats! they have since been discarded]. Anyone need a Master's thesis? [End of Article] In Nat's most recent article, he states that "if you do a good job of cutting the cores, or purchase professionally cut cores from Featherlite , very little sanding should be required..." That may or may not be true. First, any core cut with a hot wire saw will have dips and lumps that increase in severity towards the center of the core. Not infrequently, the irregularities violate the "1/16-inch per one foot span-wise" quality control criterion and result from wire lag. The only way to avoid these irregularities is if the tension on the wire can be set to infinity. Obviously, this cannot be done. As the wire travels over the templates, the center of the wire lags. If the wire is traveling towards a thicker section of the core, a dip is created in the center; high spots are created when the wire is moving towards thinner sections of the core. The high spots can be sanded to the proper contour by using a sanding spline on the core before the templates are removed. You're stuck with the low spots. I have yet to find any builder who claims that he or she can turn out a perfect core. There is another problem. In discussing the matter with Jeff Russell at his Chino Builder's Seminar (speak up, Jeff -- don't let me put words in your mouth!) Jeff thought that a 1/16" burnback (the distance from the edge of the hot wire template to the foam core after cutting) was about the best that one could expect to achieve. Based on my experience, I would have to agree. So, here we have at least two factors -- factors that are difficult to control and that cannot be eliminated -- that will produce an irregular core. Now, the question becomes: What are we going to do about it? Nat would prefer that, after bonding the cores together, we resand them to contour. We have to be careful not to leave high points where the cores are bonded together because the dry micro joints are harder to sand than the foam itself. He suggests that we undercut the joints prior to sanding and then refill them immediately prior to glassing. This is all well and good, but there is no reference available to hold the airfoil contours. The main problem is that the cores will be correctly sized near the ends and undersized near the centers. Sanding the foam cores will remove material from the ends and from the areas near the joints, resulting in an undersized core. Also, as the center templates have been removed, holding the exact contour of the airfoil will be difficult. Trying to sand the entire canard or entire wing span against the end templates is a tough job and foam, being as soft as it is, is easy to oversand. Anyone using Nat's procedure has to proceed very slowly and cautiously, especially when considering how easy it is to take off too much foam. If, on the other hand, you choose to hardshell your airfoil cores, you have the opportunity to fill the dips in the cores prior to glassing. This results in straighter fibers and a stronger wing. Moreover, you have a reference with which you can work. You know that the cores will be low in the center and correct at the seams, so you just spline sand the micro until the foam begins to appear at the seams. As you sand, you apply the 1-foot ruler check (which you can do with far greater accuracy on a sanded micro surface than you can on a bare foam surface) to ensure that you have a perfectly straight core. If you don't, you keep sanding and filling. Yes, micro is harder to sand than foam, but I consider that to be an advantage, not a drawback. It means that I have the ability to hold tighter dimensional control without oversanding. When sanding foam, a `whoops' produces a low spot quickly; with hard shelling, it does not. On top of that, you have the spar cap to contend with. After the spar cap has cured, most of us strip the peel ply and sand the spar cap to remove the bumps at the ends of the individual plys (I use a Black and Decker Palm sander -- it takes me about 3-4 hours to do a good job). Eventually, we get the cap to pass the dip/bump criterion but the spar may be above or below the surface of the core slightly -- mine caps are usually above the core by 1/32"-1/16". If the caps are below the overall core, you can always sand the core down at the expense of distorting the airfoil. But if the caps are above the core you can either sand the cap some more (which I don't recommend -- this will weaken a critical structure) or you will wind up with a longitudinal bump that will have to be filled later. As the wing skin is laid up across the bump -- UND at roughly a 30-degree angle to the spar -- you will wind up with a bump in the skin fibers adjacent to the spar. This bothers me. It puts a stress riser exactly where the skin stresses are supposed to be picked up by the spar. I know -- the plans say that minor dips and bumps normal to the spanwise direction are OK, but it still bothers me. Hard shelling permits you to blend the foam core perfectly into the spar cap structure. This results in straighter fibers and strongers wings. Yes, hardshelling takes more time. But most of us are not rushing to get our airplanes into the air so that we can display them at air shows. We would prefer to take the extra time if it will improve the quality of our aircraft. In that hardshelling allows us to achieve a far straighter core prior to laying up the skins (thus increasing the strength of the skins and the overall wings, to say nothing about reducing filling later), I believe that the time is well spent. Of course, this is a decision that each of us has to make. Which brings us to Nat's third point: poorer peel strength. Here, confusion still seems to reign. Nat now seems to think that hardshelling is a "very bad idea" whereas in my contact with him three years ago, as published in CSA, he seemed ambivalent. I'm not sure why the dramatic change in opinion, although he does state that he is recalling Burt Rutan's opinion on the subject. At Burt's birthday party , builders seemed to indicate that Burt had changed his opinion from being against hardshelling to being in favor of it. One builder thought that Burt believed that hard shelling was the preferred method. My own experiments indicate that hard shelling produces a ***superior*** structure. I tried to contact Burt before sending out this message but Tanya was not answering the phone. Perhaps someone who knows Burt or Mike better than I do (almost anyone) could speak with one of them to get the latest opinion from Mojave. Nat argues that hardshelling results in a mechanical bond between the glass and the shell. True. He also argues that a normal layup produces a chemical/mechanical bond with the foam core. Also true. But, this may miss the point. The overall strength of the structure is determined by its weakest link. Which is weaker...the mechanical bond between the glass and the shell or the foam itself? In my experiments, the foam was the weakest -- delamination occured because the foam tore. On the other hand, Nat states that Burt believes that the mechanical bond to micro is poor and that the internal strength of micro is poor. Nat and Burt may have a point here and, as builders who are hardshelling , we may need to concentrate on these two factors. To improve the mechanical bond to the shell, I always sand my shells with 120 grit sandpaper prior to bonding. To improve the internal strength of the dry micro, I mix it somewhat wetter than what most people would call `dry.' My experiments show that, the way I mix dry micro, it is stronger than the foam. How about the way ***you*** mix dry micro? You see, the problem may be one of terminology. We don't mix dry micro quantitatively -- we do it by eyeball. Perhaps the point at which the internal strength of dry micro becomes less than the internal strength of polystyrene foam lies within our eyeball mixing range? One thing that crossed my mind after reading Nat's article had to do with the strength of dry micro. When I hard shell, I slurry the foam and then spread dry micro over the slurry. However, as I said, my `dry' micro isn't exactly dry. It's somewhat drier than the micro that I use for bonding cores. It barely flows (creeps) off a mixing stick, but I have not added so many microballoons that the mixture refuses to accept more. Is it possible that really dry micro is structurally weaker than polystyrene foam or a glass -to-foam bond made with slurry? I suspect that the answer is yes. Another question that needs to be looked at is the long-term consequences of building a structure that has been stiffened with the use of dry micro. Stiffening a structure redistributes loads and sometimes those loads migrate to places where the designer had not intended them to be, causing the structure to fail. This is why it is inadvisable to add extra plys to a layup to make it stronger. You may, indeed, make the layup stronger but the overall structure may be weaker. In hardshelling an airfoil, my experiments indicated that the oveall layup was stiffer. At best, this may result in an airplane that bounces a bit more in the thermals. At worst? Will the hard shell crack and grind itself up under the skin over the long term (probably not)? On a microscopic scale, will the stiffer structure distribute concentrated loads into the foam, causing foam failure? I have no idea. I've never seen anyone actually perform experiments to determine the consequences of hard shelling on a structure that is being subjected to repetitive stresses. Perhaps the bottom line is that there appears to be a large number of Vari-EZs and Long-EZs that were constructed using the hardshelling method. I have not seen a pattern of these aircraft undergoing delamination failures, and, to the best of my knowledge, no such pattern has been reported in the literature. Therefore, I would have to conclude that hardshelling does not cause the delamination failures that seem to concern Nat. However, to persue the matter, I'm going to post a message to rec.aviation.homebuilt to see if anyone knows of delamination failures over a hardshell. I'll forward anything I hear. In the meantime, this is a subject that really interests me. If anyone wants to persue it, either conceptually or experimentally, please write. I don't have access to testing facilities other than what is in my garage, but perhaps we can dream up a way to make my experiments more accurate. Also, if anyone knows of any literature that has been published on the subject, I'd love to have the reference. Jim Cullen Cozy Mk IV S/N 0076, started 09/03/91, now working on the wings. Date: Tue, 17 Sep 96 18:00:46 est From: "Larry Schuler" Subject: COZY: Hardshelling -- Caution -- A Long Article. James Cullen wrote a lot that has been deleted for the sake of brevity......> :-) Your disertation said nothing about the current use of alcohol in the hardshell slurry/micro. If you try some additional experiments in your garage lab; please consider testing this as well. I think we'd all like to know more. Larry Schuler MKIV-#500 Date: Mon, 23 Sep 1996 07:38:40 -0400 (EDT) From: Kenneth Brimmer Subject: Re: COZY: Hard Shelling Redux I spoke to a composit eigineer friend of mine some time ago on "hard shelling". This friend of mine is well qualified to judge both academically and about 20 years of hard research in the area. The following is his response though short. >Date: 30 Jun 96 20:20 EDT >From: bergenm@oasys.dt.navy.mil (Michael Bergen) >Subject: Re: COZY: Hard Shelling Redux >To: brimmer@erols.com >Cc: bergenm@oasys.dt.navy.mil > >Ken > >I spoke to this once before!? This is a very bad idea. What one wants >is a chemical bond not a mechanical bond as a result of this process. >Especially if this is Safe-T-Poxy (EPOLITE) being used. Terrible secondary >bond properties and peel strength. > >Mike B > > Ken Brimmer brimmer@erols.com "I am certain that nothing has done so much to destroy the juridicial safeguards of individual freedom as the striving after this mirage of social justice." - Fredrich von Hayek, Economic Freedom and Representative Government; 1973 Date: Mon, 23 Sep 1996 15:10:05 +0200 From: Rego Burger Subject: COZY: PEEL STRENGTH >Ken > >I spoke to this once before!? This is a very bad idea. What one wants >is a chemical bond not a mechanical bond as a result of this process. >Especially if this is Safe-T-Poxy (EPOLITE) being used. Terrible secondary >bond properties and peel strength. > >Mike B > > Ken Brimmer brimmer@erols.com "I am certain that nothing has done so much to destroy the juridicial safeguards of individual freedom as the striving after this mirage of social justice." - Fredrich von Hayek, Economic Freedom and Representative Government; 1973 Extract above - COMMENTS: We can get all confused with terms so I would like some comments too please. Intro. Hardshelling as I understood it was a substantial layer of dry micro on a foam surface ( dried ) then coated with a skin! Peel strength as I understand it is what I call " interply or laminate strength " Then chemical bonding is what I perceive to be the interlinking process as epoxy cures. Now : According to my understanding foam cores are the weakest link in our whole process of putting a craft together. The strongest density PVC foam has about 1Mpa of strength keeping it together. To bond with anything stronger than that is overkill! It's like trying to build a house with cement stronger than the bricks, pointless. Please note: When it comes to a mechanical bond between dry glass skins we faced with another story. Here yes, one needs to prepare with a rough surface to provide "grip strength" Nat has covered this clearly in the plans. If you did not peel ply the night before your only alternative is to sand rough with 36 grit and "elbow-grease."( labour, not an exotic release agent ) The only time I FEEL ( strongly ) that one should not have any micro between glass layers. Reason: micro is weaker than glass but almost the same strength as foam. So interglass shear will be weakened badly. Chemical Bonding: This is of no relevance to a glass to foam bond as their is no reaction between the two chemicals ( foam and epoxy ) However between two glass skins there is a linking process on fresh layups, ie. the first layer must not have dried or set yet. Some manufacturers have claimed this should not be left to more than 4 hrs after application for good results. To simply conclude: 1. Use micro on foams ( similar strength/weight ) 2. Only use micro as a finishing additive on a completed glass structure. NB. If you made a mistake and need to add a bond to a surface with micro on, SAND it ( the micro ) off! If you want to try hardshelling the dry micro surface must be treated as a glass surface, it must be treated with 36 grit before laying the glass cloth on! Home experiment: Do yourself a simple exercise, take some scrap cloth 2 ply BID or UND and wet it on a piece of window. This is a simulation of laying it on a dry glass layup. Make another sample on a scrap piece of PVC. Another on a scrap peel plied off-cut BID layup. Leave them to cure a day or two. Now take a chisel and try and remove then from their parent surfaces. The window representing a smooth bond, the PVC a foam bond and the peel plied. You would then have a practical example of the various bonds on your aeroplane! And test your own skills. I tested white polystyrene foam and compared it to The USA blue foams. The tests proved that the blue foam is 10 % stronger. And the weak white foam had a shear strength of 9.166 lbs / sq.in. If you multiply that by 144 ie 12x12 in to get it to lbs/sq.ft you get, 1319,904 lbs/sq.ft. Compare that to the Cozy's wing-loading! Micro ( 50/50 epoxy/micro ) is stronger than that! Just use it in the right place. When in doubt follow the plans. Best To all and happy building. Rego Burger Port Elizabeth South Africa Cozy Mk IV # 139 e-mail: burgerr@telkom.co.za From: "Krasa, Paul" Subject: COZY: Hard Shelling Date: Mon, 23 Sep 1996 10:02:48 -0400 I have disscussed this subject with a few people over the phone. Here's what I think: 1. The purpose of micro slurry is to provide a mechanical bond between the foam and the glass. 2. No chemical reaction takes place between the foam and regular micro. 3. If more micro is added to the epoxy by adding alcohol (hard shelling), the bond strength between the foam/micro/glass has been weakened because there is less epoxy to provide strength. Micro is just a filler. 4. I question the compatibility of the alcohol and the foam, but have not tested this combination. 5. The effects of the water in the alcohol has no contribution to the resin system and the mechanically bound molecular alcohol will eventually evaporate especially when exposed to the sun causeing disbonding, blisters, and/or delaminations. 6. If West Systems is being used, it is not a structural epoxy. My policy is not to deviate from the plans in areas that effect the structural strength of the airframe. I am a mechanical engineer and have alot of professional experience with composites. I choose not to make these changes to the design because to do so would take a lot of testing beyond making a few rudimentary test coupons. My belief is long term this will cause major disbonding that will effect the structural flight worthiness of the aircraft. I believe this process is very dangerous. With that said, this is Experimental aviation and any builder can experiment with the design as he/she sees fit. If it works, great; if it does not, he/she only kills him/herself. It's great to have such freedom :->. I have discussed this with Gary Hunter who is Shell's epoxy guru. He also thinks that this is a bad idea. If you would like to discuss "hard shelling" with him, call him at 1-800-TEC-EPON. Gary is a Vari Eze driver and the Crew Chief for Pushy Galore. Paul Krasa Long EZ 214LP !---*---! From: Marc J. Zeitlin Subject: COZY: Hard Shelling (fwd) Date: Mon, 23 Sep 96 15:34:52 EDT People; As a recent convert to hard shelling, I thought I'd throw in my experience, which seems to mitigate the worries that some people have about this practice. Paul Krasa wrote: >3. If more micro is added to the epoxy by adding alcohol (hard >shelling), the bond strength between the foam/micro/glass has been >weakened because there is less epoxy to provide strength. Micro is just >a filler. This may be correct, but I will give my experience while skinning my wings. When doing the bottom layup, the two layers of UNI wrap around the leading edge somewhat. Rather than knife trim them, I have let them cure (in the interest of not waking up at 3 AM :-) ). They were cured over hard-shell wrapping around the L.E. After dremel-sawing through the excess glass right along the L.E., I peeled the excess glass off. In both cases, anywhere the glass had contacted the hard-shell, the glass peeled the hard shell off the foam, rather than having the glass come away from the micro. I was left with raw foam. This tells me that although the micro might be less strong than it is with fewer balloons in it, it's still stronger than the foam, so isn't the weak link. If I'm willing to live with a "mechanical" rather than "chemical" bond between the skin and the spar caps, I'm certainly willing to do so between the skin and the foam. >4. I question the compatibility of the alcohol and the foam, but have >not tested this combination. It does not melt (or affect in any way) the blue floatation polystyrene, at least as far as I can tell. Given how fast the alcohol evaporates, I would not expect that there could be any long term effects. >5. The effects of the water in the alcohol has no contribution to the >resin system and the mechanically bound molecular alcohol will >eventually evaporate especially when exposed to the sun causeing >disbonding, blisters, and/or delaminations. I have found that the alcohol in the micro evaporates _incredibly_ fast. If I spread the micro on and don't get it smooth within 10 seconds, it thickens up so much that I can't spread smoothly anymore. The alcohol has a very low vapor pressure, and is very smelly. While spreading the micro, I can smell it easily. By the time two hours have rolled around, I can't smell it anymore, and the micro is _VERY_ thick and dry. After cure, the micro sands exactly like regular dry micro, and no alcohol smell emanates from the sanded micro (as it would if the alcohol were still outgassing). So, I'd guess that there'll be no alcohol left in the micro to heat up and evaporate by the time I finally get the darn thing flying :-). It's also possible to seperate the two issues - you can hard-shell without adding alcohol to the micro. This still gives you the shape and time advantages of hard-shelling - it just weighs a bit more. However, do NOT use micro with alcohol under a layup while still uncured, for exactly the reasons Paul mentions in (5). No proof, just my $0.02. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Tue, 24 Sep 96 16:17:29 est From: "Larry Schuler" Subject: COZY: Hard Shelling (fwd) Marc wrote: >As a recent convert to hard shelling, I thought I'd throw in my >experience, which seems to mitigate the worries that some people have >about this practice. >Paul Krasa wrote: >>5. The effects of the water in the alcohol has no contribution to the >>resin system and the mechanically bound molecular alcohol will >>eventually evaporate especially when exposed to the sun causeing >>disbonding, blisters, and/or delaminations. >I have found that the alcohol in the micro evaporates _incredibly_ >fast. If I spread the micro on and don't get it smooth within 10 >seconds, it thickens up so much that I can't spread smoothly anymore. >The alcohol has a very low vapor pressure, and is very smelly. While >spreading the micro, I can smell it easily. By the time two hours have >rolled around, I can't smell it anymore, and the micro is _VERY_ thick >and dry. After cure, the micro sands exactly like regular dry micro, >and no alcohol smell emanates from the sanded micro (as it would if the >alcohol were still outgassing). So, I'd guess that there'll be no >alcohol left in the micro to heat up and evaporate by the time I >finally get the darn thing flying :-). Marc, you are using 2427 as I am. We have both experienced the "kick" challenges (with multiple layers) as well as the humidity problems. What have you discoverd about the water interaction with the 2427 in alcohol - hardshelling? Also, I have looked everywhere locally for Methyl Alcohol and the only stuff I have found was at hardware stores. Marked as a laquer thinner, but label says it can be used in chafing dishes etc. The stuff does indeed contain water and a number of other additives (the label says to make it poisonous); including a rubber solvent...... Can you be specific as to manufacturer or label name on the stuff you found locally? Thanks, Larry Schuler MKIV-#500 From: Marc J. Zeitlin Subject: COZY: Hard Shelling (fwd) Date: Wed, 25 Sep 96 10:14:14 EDT Larry Schuler wrote: >you are using 2427 as I am. We have both experienced the "kick" challenges >(with multiple layers) as well as the humidity problems. What have you >discoverd about the water interaction with the 2427 in alcohol - hardshelling? Nothing. What I wrote is what my experience has been - since I'm sanding the hard shell down with 36 grit on a 3' spline anyway, any water caused amine blush is taken off. As I said, I've never had a problem. >Also, I have looked everywhere locally for Methyl Alcohol and the only stuff I >have found was at hardware stores....... >...... Can you be specific as to manufacturer or label name on >the stuff you found locally? I _think_ that's the stuff - I got it in a hardware store, and it says about the same thing on the label. I think the manufacturer is "Sterling", and it's a white can with some black on it. Comes in quarts and gallons. If I'm wrong on this, I'll let you know. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Fri, 27 Sep 1996 17:42:16 -0400 From: Nigel Field Subject: Re: COZY: hard-shell alcohol At 05:57 PM 9/27/96 EDT, Marc wrote: >People; > >Larry Schuler had asked about the alcohol I was using for my hard >shelling. It is, in fact, made by Sterling (Malden, MA 1-800-225-4444 >[or 1-800-732-3809 inside MA]). It's called "Lynsol" Clean Air Solvent >Denatured Alcohol. Says: > > Thins shellac and shellac base primers. Fuel for alcohol stoves, > lamps, and chafing dishes. > >on the front, and: > > Lynsol is 190 proof denatured alcohol..... > > USES: Shellac thinner, cleaner for shellac brushes and tools and > shellacked surfaces, epoxy and urethane finish prep cleaner > before final recoat, printing press and typewriter cleaner. > >on the back. I'd venture a guess that since they recommend it as an >epoxy cleaner, it can't have any deleterious effects on the epoxy (and I >certainly haven't noticed any). > If I may add my bit to this subject, suspect this may be Ethly alcohol which may work OK but probably contains water if its only 190 proof (5% water). I sent the following suggestion to Larry but it may benefit other hardshellers. Hi Larry, What you need is Methyl Hydrate which by it's very name is almost completely free of water. Its available up here in the Great North in most every hardware store, so I'm sure you can get it in the USA, often used as thinner for Shellac, check their paint department. Laquer thinner is very different being Toluene based and contains MEK and other nasty stuff. It will thin epoxy but will also rapidly dissolve styrofoam (wing cores). Denatured (poisoned) alcohol is usually Ethly alcohol and contains water. Iso propyl (rubbing) alcohol will also thin epoxy but its usually full of water in its marketed form. BTW I have never had a dis-bond/delam over hard shelled foam on my VE which is now 8 years old, just a small one on the canard LE from a bird strike which bruised the core. Nigel From: Marc J. Zeitlin Subject: COZY: hard-shell alcohol Date: Fri, 27 Sep 96 17:57:36 EDT People; Larry Schuler had asked about the alcohol I was using for my hard shelling. It is, in fact, made by Sterling (Malden, MA 1-800-225-4444 [or 1-800-732-3809 inside MA]). It's called "Lynsol" Clean Air Solvent Denatured Alcohol. Says: Thins shellac and shellac base primers. Fuel for alcohol stoves, lamps, and chafing dishes. on the front, and: Lynsol is 190 proof denatured alcohol..... USES: Shellac thinner, cleaner for shellac brushes and tools and shellacked surfaces, epoxy and urethane finish prep cleaner before final recoat, printing press and typewriter cleaner. on the back. I'd venture a guess that since they recommend it as an epoxy cleaner, it can't have any deleterious effects on the epoxy (and I certainly haven't noticed any). my $0.02. -- Marc J. Zeitlin Email: marcz@an.hp.com From: Lee Devlin Subject: Re: COZY: hard-shell alcohol Date: Fri, 27 Sep 1996 18:01:51 MDT > Laquer thinner is very different being Toluene based and contains MEK and > other nasty stuff. It will thin epoxy but will also rapidly dissolve > styrofoam (wing cores). Denatured (poisoned) alcohol is usually Ethly > alcohol and contains water. Iso propyl (rubbing) alcohol will also thin > epoxy but its usually full of water in its marketed form. These are the alcohols in common use. They are: Methyl Alcohol = Methanol = CH3OH a.k.a wood alchol (poisonous) Ethyl Alcohol = Ethanol = C2H5OH a.k.a. grain alcohol (non-poisonous) Isopropyl Alcohol = Isopropanol = (CH3)2CHOH a.k.a. rubbing alcohol (poisonous) 'Denatured alcohol' refers to Ethanol which is generally mixed a poison like methanol to make it unfit for human consumption. This is done strictly for tax purposes. The alcohols I've labeled as poisonous are only poisonous by ingestion, so there's not a health hazard posed by handling them. Other grades of solvents found in thinners and reducers are generally made from aromatics like Toluene and Xylene (which are both carcinogens) and ketones. Examples of ketones are Acetone, the primary ingredient in finger nail polish remover, and Metyl Ethyl Ketone (MEK). I don't think the EPA has yet classified these ketones as carcinogens, but the list now has 3500 compounds and is growing constantly. I've run Stits Reducer through a Gas Chromatograph with a Mass Spectrum Analyzer and was amazed at it's simplicity (It contained only 5 compounds) but it's hardly worth mixing your own at $25/gallon. As for the purity of Ethyl Alcohol, you could go to your local liquor store and demand Everclear. A little for you, a little for the Cozy...but not in that order :-). But with all that taxation it's likely to get expensive. Lee Devlin Date: Sat, 28 Sep 1996 18:40:44 -0400 From: Jim Hocut Subject: Re: COZY: Hard-Shelling/Filling (fwd) Marc Z. wrote: > >I can't resist here - Steve - you been sleeping? :-). > ..... > > >PS - Sorry for the zing, Steve, it's just that the discussion was so > recent! :-). Actually, I believe Steve had a new twist on hard-shelling that hasn't been touched on, FINISHING a plane (Outer Shelling ???) (so far the discussion has centered on hard-shelling for the purpose of doing a subsequent layup). Personally I'm a little bit chicken of this beacause hard shell is definitely not as hard after cure as plain dry micro. Since I'm at least a couple of years away from being ready to worry about it, I've been toying with the idea of trying this on a couple of scraps, having the pieces painted, and subjecting them to abuse to see how the finish holds up. Jim Hocut jhocut@mindspring.com