I have not flown for several years and thought it a good idea to build a kit before flying again. This to remind me of the finer points of flying. One of the things I have forgotten is the use of epoxy to seal the firewall. I remember that in mixing the epoxy one could thin it to allow more work time and to allow it to be brushed smoothly onto the firewall. This all to fuel proof the engine compartment.

The question is "what do you use to thin the epoxy?" I appreciat your help.
Dave14