Epoxy won't stick to...?

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Well-Known Member
Apr 22, 2009
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Hey all...

I'm planning on laying a layer of 1oz cloth on some balsa and I was hoping to speed up the process by doing both sides at the same time. That being said, I'd need to lay down a "wet" side on a surface. The plan is to coat each side in light glass and epoxy, then sandwich the fins between the table and a heavy book. Those surface will obviously need to be protected. So what should I use? Wax paper? Will a ziploc bag work?

The way I see it, by sandwiching the fins with plastic or non-stick surface, I will have an ultra smooth finish once the plastic/non-stick surface is peeled away.

Any ideas or suggestions as to the best non-stick surface would be appreciated. Thanks!
I have never done exactly what your describing b4, but the other day i set something with epoxy curing on it on wax paper and when it was completely cured i picked it up and it came right off the paper. i wouldn't trust a zip lock bag, i have never tried but i think epoxy will stick to the plastic *very* well, and then you’d be in trouble:D.
i would try just putting a little epoxy on the wax paper and let it cure, then see if it comes off. it be better than finding out the hard way!
the only other comment i have is make sure there are no wrinkes in the wax paper (common sense), and I’d tack the edges down so that you know the paper will stay flat... just don't do it on your kitchen table;)

What you've described using the wax paper works like a charm.

Make two pieces of cloth that are large enough to accommodate all the fins you want to do at once with some room between the fins (about 3/4" or more). On a very smooth surface (*), lay down a large sheet of wax paper then one piece of cloth on the wax paper. Liberally coat one side of the fins with epoty and then lay them out on the cloth with the wet epoxy down. Now liberally coat the other side of the fins with more epoxy, lay out the other piece of cloth, and then the other sheet of wax paper. Now put another very smooth surface (*) on top of the waxpaper-fiberglass-fins-fiberglass-waxpaper sandwich. Finally, put something HEAVY on top of all of this. Allow to cure overnight.

Unstack the pile. If the epoxy is still tacky, let it cure a couple more hours. When no longer tacky, take out the fins and trim the excess using a sharp hobby knife. If you do this trimming while the epoxy is still green, it is very easy to get a nice clean edge. After another day or so of curing, you can sand the edges smooth. There should be enough resin soaked into the edges of the fins to make them almost bulletproof.

Bonus tip: If you are doing through the wall fins, you can use masking tape to protect the tab that goes through the BT. Just cover the tab sides and edges with tape. You will be able to easily trim the green resin/cloth along the tape and remove the tape to reveal the nice soft wood suitable for passing through the slots and bonding.

*- Whatever texture the surfaces you use on the layer outside of the two wax paper sheets will transfer into the laminated surfaces. That is, if you use a piece of plywood, the grain will appear in the laminate. If you use a book, the texture of the book will transfer to the laminate. For this reason, when I do this process, I use sheets of thick window glass. You could also use the scraps of Formica-type laminate, for example, like the sink cut-out from a counter top probably available as scrap from a home center (Lowe's, Home Depot).

HTH, --Lance.
Also, I would personally advise against going for an "ultra smooth finish" from the glassing process. Odds are if you get one of those, you've used too much epoxy, thus adding unnecessary weight (may not be the case with a very fine, yet dense weave, though). Remember that the strength is in the glass, not in the epoxy (go ahead and pour a thin layer of epoxy on a coffee can lid and let it cure, then bend the lid--it's not that strong on its own). You will almost certainly get at least part of the weave of your cloth in the finish. Remember, though, that primer and/or fill n finish are lighter than epoxy.
I have done this and you dont get a super smooth finish. ALot of times the surface is mostly smooth except for the pin hole which stay. I would use wax paper but a shopping bag also works well. I once use a shopping bag as a balloon to internally glass something, worked well.
I find the poly-bags you get in supermarkets work well, too. I use them to stand my tools etc on; I can put down a epoxy filled brush or lollypop stick, and know it won't become a 'permanent feature'.
Eugene -

Check out some links on vacuum bagging, a technique used by RC plane builders. Wax paper will probably do just fine, but there are release films specifically designed with fiberglassing in mind.

It's probably not worth the bother, just for some fins, but it's interesting reading nonetheless.

Here's one link:

I just went through this process and wax paper can't be beat. I also used two sheets of glass to sandwich - I didn't get smooth, I got the weave of the glass. Also - to get everything to soak in and adhere nicely I heated the fins up with a heat gun - poured the epoxy on the glass and the hot fins wicked the epoxy through the glass like a dream. Then I sandwiched and am very happy with the results. I also used the 206 Slow Cure hardener from West System - heat makes epoxy cure faster so keep that in mind.

Originally posted by edwardw
heat makes epoxy cure faster so keep that in mind.

If you use heat on epoxy, say with a heat gun, while its curring will it weakin in any way? just wondering... i've heard of this before, but thought it better to ask before gunning anything;)
Here is where I got my information - Page 22 of the West System User Manual and Product Guide.

"There is a better solution to get good penetration without losing strength or moisture resistance. We recommend moderate heating (up to 120 F) of the repair area with a heat gun or heat lamp before applying epoxy. On contact with the warmed wood, the epoxy will thin out, penetrating cavities and pores, and will be drawn even deeper into the pores as the wood cools. Although the working life of the epoxy will be considerably shortened, slower hardeners (206,207,209) will have longer working life and should penetrate more than 205 Hardener before they begin to gel. When the epoxy cures it will retain all of its strength and effectiveness as a moisture barrier..."

I amnot sure if I am corret here but I have heard that when curing epoxy with heat you can actually *** strength
The technique West System says to use is not heating of the Epoxy, but of the surface. This wicks the epoxy in. I don't know what happens if you heat the epoxy - probably bad things. And 120 F isn't too hot - warm-ish to the touch. I have an infrared temp detector I use for cooking so I just shoot the temp on the fin to see. Usually I heat it up a little more, then let it cool back to about 110

A few things can happen to West Epoxy when heated.

It gets very thn and runny so it soaks in real well.

The bad thing is it can "flash cure" this is my term, it cures so fast that it will almost foam and outgas, ruining the part. It actually starts to smoke!...throw it into the driveway FAST!


I see, I wasnt using west systems i was using US composites. I always put it next to the fire in my basement which is cranking at about 1000 degrees F. The stuff doenst get that hot but it does get very hot. I have never had bubbles except the ones left over from mixing. I like it because the dry time is cut in half
last May I was doing some hot tub repairs. ambient temp was over 100 and the surface of the hot tub was, well, hot. it felt hot to the touch so must have been > 120o?

so I mixed the resin (105) with 1/2 the amount of slow hardener I had been using (206), and it still went off in just a few minutes!! turned to jelly right before my eyes - that was kinda neat. the smoke was terrible. I thought for a few seconds I had made a big mistake and there was going to be a big fire!

note to self - get a cool drink and take a break.