I'm glassing for the first time and I'm starting by making some main retracts doors for my TF GE Corsair. Following Luke's "Royal" post, I've laid down some Monokote over the sheeting and began laying two courses of general (not sure of the weight - it's from Lowes) f/g adhered with Elmer's Epoxy Resin. The resin spreads like thick frosting and has me concerned that multiple layers of f/g will not adhere together very well. It's still setting up and I'll know for sure tomorrow but, in the meantime, do the experts use this technique to make hatches/doors or should the resin be thinned with denatured alcohol or is another technique better for this purpose?

By the way, I intend to glass the wing and fuse with .75oz f/g using MinWax PolyCrylic but I didn't think that would be strong enough for a retract door.

Thanks for help. Gotta love RCU!



-kwz

I've not used Elmers brand epoxy resin before. But what you describe sounds a bit too thick. I use another brand (West Systems) which is about the consistancy of thick syrup. I've also used 30 minute epoxy from the hobby shop for small fiberglass parts. I wouldn't use anything faster than 30 minute, and prefer a slower epoxy. It should soak the fiberglass when spread with a brush. I do thin it a bit, perhaps 15-20% denatured alcohol. Thick frosting sounds too stiff. You can try thinning. Worse case scenario is that you'll have to lay down a new piece of monocote and try again. I would lay up at least 3 layers, perhaps even 4 of glass for a retract door, and use a plastic card to squeegee off as much resin as you can. Also, the squeegee will help to make sure the layers are well bonded and you have no air pockets. If you see any whiteish spots, add more resin and squeegee again. I would agree that PolyCrylic would not be the proper product for making free standing fiberglass parts.

Scott

The general rule is that the strength comes from the glass fibers, not from the resin. All the resin has to do is stick the fibers tight to the surface, and when the part is stressed, it's the fibers that do all the resisting. I've used both polycrylic and epoxy for finishing sheeted parts, and can see advantages either way. I tend to use epoxy, mostly because I have better confidence in primers that are formulated to bond to epoxy. But I've been happy with my polycrylic jobs as well, after adding a few finish coats. Fast drying time is a major advantage, as is water clean-up.

I'm not familiar with the Elmer's product, but thick viscosity sounds like it would not be so helpful. Experienced glassers use laminating or finishing formulations, which have a fairly thin consistency. I tend to use West products, which are also fairly thin, and have a variety of hardeners (fast, medium, slow cure). I buy it by the gallon. Shelf life is pretty good--some of my resin is at least five years old, and still good.

Thinning with alcohol is normally aimed at spreading the epoxy in a very thin coating, thick enough to bond the glass cloth to the surface, but thin enough to keep the weight down. Epoxy can add a lot of deadweight if you're not careful. But where you're making up a piece entirely of fiber/epoxy with no substrate, you need enough epoxy to fill the weave of the full laminated thickness. In making up retract doors, I'd think thinning with alcohol is not the way to go.

The best way to bond additional layers of glass is to do all the lay-up while the resin is still semi-liquid, before it starts to set. Start by coating the surface with epoxy, then lay the cloth down on the wet surface and stipple it down with the point of the brush, or with a fine-textured paint roller. Make sure you drive out any air bubbles under the cloth. Then when the first layer is down, add the second, then the third, stippling or rolling each one down into wet resin. Obviously you want a slow curing hardener for this kind of work, which is typical of laminating & finishing products.

Thanks Saramos and MajorTom.

This Elmers Epoxy Resin stuff hardened up nicely and the two plies seem to be laminated well but I have doubts. Each component of this resin is like peanut butter and, when mixed, remain like peanut butter (no soaking but plenty of squeegee-ing). Since it's a small project, I'll try some experiments - thinning this stuff and using plain 30min epoxy. I can always go back to the stinky automotive resin (for just the doors) if I get desparate.

-kwz

I use the Elmers Epoxy resin regularly...in fact, just finishing up a cowl for my latest build using the stuff.

kzaiser is right...it's a bit thicker than most. However, I tend to prefer that, since I figure that I can always thin the stuff up, or leave it thicker, making it pretty versatile.

Here's some tricks I've picked up along the way:

1) Alcohol, as mentioned above, is the "standard" thinner. I mix about a capful of alcohol to 3-4 ounces of Elmers resin...though, that's by no means exact....whenever I'm doing the basic layup.

2) Another VERY powerful thinner is acetone. Do be sure, however, to read the various warning labels...acetone's good stuff to be careless with. Use it in a WELL ventilated area, and keep it away from any ignition sources. Its major advantage over alcohol is it tends to stay "in solution" with the epoxy a fair bit longer...meaning, the epoxy stays thinner longer, allowing more working time. Note, however, it also tends to widen the gaps between epoxy molecules a bit more...so you'll get a lighter, but not quite as strong, coat.

My normal process with the Elmer's goes like this (please note, this is for casting external parts on a plug, not laying up parts inside a mold)

I'll make my plug, wrap it with masking tape, and then coat the plug with cold vaseline (insert rude joke here). Then, I'll lay a layer of cloth on the plug, and liberally coat it with alcohol-thinned resin. At this stage, I don't do a whole bunch of smoothing or anything, but we don't want globs of epoxy for obvious reasons. A regular cheap paintbrush seems to work best here for me.

Next, when that layer is still tacky, but not "wet", I'll lay the second layer of cloth down, and then coat it with acetone or alcohol thinned resin, depending on how concerned I am about weight, and how smooth I need the part to be. Acetone thinned resin = lighter, smoother, but less strength.

I let the part then cure for a day or more, until the shell is nice and hard, and not tacky. At that point (and this is where I like the versatility of the Elmer's) I'll mix up a very small amount of Elmer's resin with no thinner at all...in fact, depending on the situation, i might even mix some West's microballoons in to make it even thicker. This I spread straight on the part, no cloth, and then use various tools (a foam roller works VERY well for the finishing touches) to squeegee/roll/spread the epoxy as thin as I possibly can. This last step fills in any gaps in the weave, as well as any minor depressions, etc, that may still exist. The trick here is to work quickly (the elmer's will go off in about 20 minutes I've noticed) but forcefully...you REALLY want a VERY thin coat...mash it down GOOD with that roller, etc. You're not looking to build any strength, and the straight resin can add weight in a hurry...you just want the thinnest layer possible to fill in the weave.

Once that's done and cured for a couple days, I'll usually shoot the part with a LIGHT coat of primer right away...for me, this helps highlight any areas that may still be rough, or need filling/sanding, etc. Again, I'm not trying to prime the part, just highlight imperfections. From there, fill/sand/finish with your preference of paints and fillers.

By no means is this the only way of doing things, but it IS a method I've had some success with using the exact same cloth AND resin you're using.

Well, after some experimenting, I think I'm 'one and done' using Elmers Epoxy Resin.

I used it both full strength (peanut butter) and diluted with De-Nat Alc (epoxy-like). The former was strong enough but so opaque I could not see lines or cutouts through four sheets of f/g. The latter was only slightly less opaque but the laminations created were too soft/flexible - like a soft baked cookie.

The undiluted 15min epoxy produced a much stiffer, far more transparent lamination. This combo will allow me to begin cutting the sheeting out to the correct shape and then lay the f/g laminate over it and trace easily. Seems perfect for my retract doors.

Can anyone expain the different characteristics of Epoxy & Epoxy Resin (the more liquid stuff) when used with f/g?

There are many ways to formulate an epoxy product, emphasizing various properties, depending on the intended application, putting in or leaving out various additives. It would take a polymer chemist to detail the possibilities, and maybe one such will come in and tell us a bit about all this.

'Epoxy', as I understand the terminology, is the cured plastic end result. 'Epoxy resin' is what becomes 'epoxy' after it has been thoroughly mixed and reacts with 'epoxy hardener'. So the resin is not epoxy, strictly speaking, nor is the hardener epoxy, but they combine and react chemically to form epoxy.

When you thin epoxy with alcohol or some other solvent, mix thoroughly, then spread it out in the thinnest layer you can, the alcohol easily evaporates before the epoxy cures, having a large surface from which to escape. When you form alcohol-diluted epoxy into a multi-layered lamination, you have more alcohol concentrated in a more three-dimensional volume, with less surface from which to escape. That leads to the epoxy curing before the alcohol has completely evaporated, giving you a more flexible product. Most likely the alcohol will continue to evaporate over time, perhaps stiffening the piece as it goes. Or maybe not. In any case, my practice is to thin with solvent only when I am putting a glass finish on, and not for structural laminations.

Thank you for that explanation, MajorTom.

It sounds like the Elmers epoxy you got included some fillers (perhaps colloidal silica). Most likely it is formulated as a thickened adhiesive which will not run on vertical surfaces, or for use as a gap filler. For use in laminating layers of fiberglass, you will be best off with a clear 30 minute or slower formula. If you plan on doing a lot of glass work, you might look into the West System products. They sell a basic resin, then a selection of hardeners for various uses (quick, slow, extra slow) and a selection of fillers (microfiber, silica, graphite, aluminum). For making fiberglass parts and for glassing planes, I use the 105 resin and the 207 hardner. I also use thier metering pumps. There are a number of online sources, here's one:

http://www.cstsales.com/epoxy_systems-ss2.html

Scroll half way down the page for the begining of the West System products

Scott

Thanks Scott. For now, I plan to epoxy/glass just the retract doors. The rest of the fuse and wing will be glassed with p/u to save weight. If I don't like the outcome, I'll definitely experiment with that West product.

-kwz

Note: Elmers DOES state their mix is good for vertical surfaces. Wish I'd know - could've saved $20!

HELP!!!! Boy do I have MESS

I bought Elmers Fiberglass Resin ( Lowes) and mixed per instructions, 14drops of hardner to 1oz of resin. Its been 4 days now and the stuff is SILL sticky. I tried another sample run and got the same results. It does NOT say epoxy but it does say it hardens ready to paint in about 2 hours.

Any body know what the problem could be??

Thanks,
Bill
GearuP

It sounds like polyester resin (14 drops) instead of an epoxy. You can get polyester resin that is made for multiple layers and it stays slightly tacky, so you can keep adding layers. What you want is a finishing resin. Also if it is a polyester, it will not set up over some epoxies. In those areas, you need a barrier layer, like a thin film of white glue.

It could also just be old. Polyester resins have a definite shelf life so if it has been sitting around for a long time, using the bare minimum of MEKP to kick it will take quite a long time if ever to cure.
Best thing to do though if you want to use polyester is just get a new can from Sig and skip most of the "crap" found in local hardware stores. Most times they're a slightly thickened version used for auto and boat repair. Especially if sold as a kit with the cheapo 6 or 8 oz general purpose glass cloth. To get the proper flow you would need to add some styrene monomer which is the proper reducer for polyester resin to get it to flow correctly. I have used clear casting resin in the past in a pinch. You can usually find that in an arts and crafts supply store (Michael's or Ben Franklin etc.).

As for epoxy, finishing resin is the tool of choice there. ZAP Finishing resin or if you want to buy some bulk stuff that is as good or better, $32 gets you a 1.5 quart kit from John Greer and Associates (Kit 300/21). Here's their website if you like...

http://www.jgreer.com/

Good luck.

Hey John
Thanks for the feedback. I called Elmers ( emailed ) and the reply was "try some heat" which I had already done. I returned the product to Lowes and got a refund.

Thanks,
Bill