There is absolutely nothing wrong with using drug store alcohol to thin epoxy. As stated before, we aren't doing it for strenght, anyway. I also have 9 airplanes in my hanger, all of which (except one) have fuel proofing using the 90% isopropanol thinned epoxy method. No problems at all, and I don't suspect that I'll start having trouble now that I've read this thread. Some people like to over analyze stuff too much. The one plane that wasn't thinned with epoxy was thinned with heat--a method I learned from here on RCU. I must say, heat will make it every bit as thin as alcohol will, so from now on, I think that will be my method of choice--except for those hard to reach areas like fuel tank compartments in arfs, where you need it to be thinned before it hits the wood.


However, if you want to use alcohol, go ahead. You aren't going to hurt anything. Rubbery messes occur when the epoxy isn't mixed properly (not enough hardner, etc.), not because it was thinned. Alcohol may increase cure time, but will not prevent curing. I also fail to believe the alcohol gets trapped. With the heat generated by curing, I would imagine that most, if not all, of that alcohol evaporates. And the water? How much water are we possibly talking about? Especially with 90% stuff...