Great info, thanks much. I actually was in the Bondo section of Walmart yesterday, thanks for steering me away.
I suppose there are different techniques for doing this. This video: (snip) was interesting, although it does not specifically involve rockets. Unlike Tony, who first put epoxy on the rocket then laid the fiberglass over it, this guy put down the fiberglass first, then applied epoxy. He also dilutes the epoxy with alcohol to make it like water. He didn't wear gloves.
I was going to recommend exactly that video. As Timbucktoo just said, painting resin on first helps the glass stick and I had a lot of success with that. I did resin - glass - more resin - squeegee/wipe and it worked great.
Wear gloves. Epoxy is less dangerous than polyester but it's still not something you want on yourself. People who work with it unprotected can develop a severe reaction to it (to the point that they can't work with it any more). A box of nitrile gloves is like $7 for 100 at Walmart. Just get the gloves and wear them. And if you end up with epoxy where it shouldn't be, alcohol works great to take it off. I used isopropyl but denatured alcohol is even better, I think. I also thinned my resin like the guy you posted (using 90% isopropyl) and it worked great.
I assume I need to sand down the existing paint on the rocket before applying the glass? And wax paper is not an adequate substitute for peel ply or mylar?
Yes and yes.
Longer version: Sand off the paint if you can. Wipe everything down with a tack cloth or damp rag. Unlike with paint (where you want a mostly-smooth surface with just enough roughness for the paint to stick) you want a nicely roughed-up surface for the glass to stick to - it'll cover up any roughness. I went over the pieces I was glassing with 100 grit, I think.
More tips: The guy in the video above uses a razor blade to trim excess fiberglass. That works, but I got impatient on my first practice piece. I said "This feels leathery....i guess?" and started cutting and the glass started coming off. DO NOT try to trim or do anything while the glass is still even remotely sticky. It should feel dry before you start trimming it. I had more success by letting it cure overnight and then sanding the excess away, particularly on the fins. I used pieces that overhung the edges by 1/2" or more, let it cure overnight, then sanded along the edge of the fin, with the sanding block at a 45 degree angle to the fin. The result is that the sanding "cuts" the excess fiberglass off. Go slowly.
I don't know if wax paper works, but I know some folks use parchment paper because it will not stick to anything. Again, practice with some scrap and you'll quickly find out what works. I think I would be ready to try using parchment paper if I were doing a flat piece - just layer something hard and smooth, then parchment, then the glassed piece, then more parchment, then something hard and smooth and heavy, then let it cure for 24 hours. But something complex like a built rocket? Yeah, I would spend my time and effort sanding instead of peel-ply-ing.
Another trick I figured out: When you do glass your rocket, glass a piece of scrap as well. Doesn't need to be big, just a little piece of wood is fine, but it will work as a tester. Drying times can vary quite a bit with temperature (literally 10 degrees can be the difference between "it's done before supper" and "it's done before bedtime")... and I'd much rather say "This looks dry, let me double check" with a scrap piece than with the rocket.
Also - After you've glassed everything, you'll probably want to fill it. Imagine wrapping your rocket in a wet piece of denim. Think of how the surface would feel and look ... not quite ready for paint. The heavier the glass cloth, the more pronounced the cloth texture is. Sanding will help a bit, but you can't really sand off the texture or you're sanding into the cloth and weakening it. There are two ways to address this:
-What I did, which is kind of like what they call gel-coating, I think: Once everything's cured and you've sanded off the imperfections, mix up a nice batch of epoxy and paint your rocket with it. It will act like a thick paint that covers up all of that weave. Keep in mind, though, that epoxy is pretty thin and will run. What I did was 4 sessions (which took forever but came out really well) because it's a four-fin rocket... basically paint one side of each set of fins at a time. So if you have a four-fin rocket and you're looking down at it, you have two fin-sides facing north, two fin-sides facing east, and so on. Put the rocket so the north-facing fin sides are horizontal and facing up, then paint them with epoxy. Let cure, rotate 180, paint the other sides. Let cure, rotate 90, paint the up-facing fins. As long as the surface you're painting is flat and horizontal, you're good. One of the things I found when I was doing my test bit was that if I painted on resin and had the rocket horizontal and the fins making an X from the back... all the epoxy runs down and leaves the fins uncovered and the body tube coated with a THICK layer.
-What they do in body shops, which is smearing a layer of filler over the glass. This will give you a smoother surface and you can (I think) do the whole rocket in one shot. BUT you'll need to double-check the protective gear (I think it's the evil polyester again) and practice a lot. Also that stuff ain't cheap - I think it was like $30 for a can of the good stuff, and you already have a big jug of epoxy anyway, so that's basically free
