Yesterday I was making a pair of Sapele doors which are bowed by about 1/4" chord depth across 11". I was veneering the shaped solid Sapele core with fiddleback veneer of the same species. Since they only needed to be 22" long each, I just shaped a 48" long board, rather than two short ones.
I had cut the veneers to 22" so I could book match the face, and was using 1/8" Masonite hardboard for cauls with a thin plastic sheet between, and using thickened epoxy for the adhesive.
This plastic sheet is so thin I have to turn the fan off to get it unfolded and in place and usually taped to the platens. I didn't have the fan on yesterday, and since this was such a small project, after rolling out a heavy coat of epoxy, I just folded it around the bundle, placed the platens on both sides, and taped them down with masking tape around both ends.
Somehow in handling, the plastic film, I guess while taping the top convex face, it bunched up along the centerline. When I took it out of the bag, I found the hardboard was bonded to the face veneer across 6" x 48", and it wasn't about to be pried off.
After saying a few choice words, I started considering my possible options to save all of my time invested. I at first thought about using the power-plane to get rid of most to the hardboard, then sand away the final few thousandths. Then I though about using the heat gun, but didn't really expect that to work through that much depth, plus if it softens the epoxy between platen and face, it might just soften it between face and substrate, but it was worth a try.
I am EXTREMELY happy to report that the heat did the trick, and it didn't take very long. I was using one of those stiff painters scrapers that have a bend half way down the blade to pry it up right in where the heat was being applied.
I know probably none of you use epoxy to veneer with, but there is often discussion of using an adhesive which is reversible. Most epoxy starts to soften around 200º if I recall correctly. This is the first time I've every used heat on epoxy, so it was a learning experience for me, and I though I'd share it for those of you who are capable of learning from others mistakes instead of having to make all of them yourself.