just a guess but normally as epoxy cures various gasses are released. I'd try it at room temp.
j

Again, like I posted on TRF, maybe try a gelcoat finish rather than straight epoxy? It's designed as a finish layer, and as such should not bubble.

Yes, outgassing is the issue. You can try reducing the temperature of the cure to slow it down enough so that they don't form or you can try heating it up to accelerate the outgassing and get it done before the epoxy has the time to gel. With West Systems, it's going to be one or the other with 205 or 206 hardener. Gel coat is really the intended finish for epoxy, however, it's a royal pain to do compared to just doing the epoxy. The best thing is to use West Systems 209 hardener - VERY clear, doesn't yellow and extremely slow to gel - 8 hours or more and 36 hours to cure, but it apparently doesn't bubble.

Warren

Warren,

Thanks for the input. I have also been looking at the 207 hardener as an option but I can't find it anywhere in the Boulder/Denver/ Ft. Collins area.

Since I am adding pigment I think I can probably handle a little yellowing.

On this rocket I think I am going to have to give up. I already have the resin layer from the vacuum bagging, then a top-coat that bubbled and I ended up sanding down. And a second attempt that I am dealing with now.

I am worried that another attempt will just keep adding too much weight.

Do you have any 207 or 209 that I could play with?

I've never used 209 on a rocket - the last time I used it was when my hobby was building boats (whitewater and fishing drift boats, mackenzie-style dory) and at that point I ordered it off the web from a marine supply place on the east coast. My supply is long gone and I haven't seen any in stores. I buy most of my West Systems from McGuckin's hardware or occasionally that plastics place in Ft. Collins.

I have heard of folks hitting it with the heat lamp - up to 130 degrees or so, for 30 minutes or so, to thin the epoxy and speed up the outgassing, but it will also accelerate the cure. On my own projects that I've tried this with, I do the top coat, sand down and then spot fill all the popped bubbles with more epoxy, resand the spots and repeat until done - then spin sand and wet sand the airframe down to 1800 before waxing with Future floor wax for the final shine. I've heard of people taking it down to 2000 grit and then using jewelers rouge and rubbing compound to bring the gloss back up. The problem with epoxy as a finish layer though is that it is UV sensitive and will eventually crack and craze unless you use additives that make it UV resistant - all of which color the epoxy, usually black. You want something like a urethane clear coat or similar on top. These are similar to epoxy, but not nearly as UV sensitive. At the least a few coats of a clear floor wax should be used to protect the epoxy.

On the Composite Rockets list server group on yahoo groups, someone recently posted a detailed description of clear epoxy finishing on carbon fiber that looked like it avoided the bubbles issue.

Since you're painting it, why bother filling with epoxy? Why don't you just use the Bondo red glazing putty. If you simply must fair out the surface with epoxy, mix a fairing compound of epoxy and glass or silica microballoons. This makes an opaque white mix with similar handling characteristics to bondo and sands nearly as well. The microballoons seem to cut down on the bubbles when laid down in thin layers and you'd use a squeegee or credit card to apply it.

Warren