I started using, MAS on the ChLT18 I'm building - it came with the kit. Since I managed to waste/abuse a fair amount of the stuff (extra unnecessary layers on the inside, mixing too big a batch for the task at hand etc.) I ran out after glassing the outside of the hull. I wanted to put a second layer of epoxy before sanding, and didn't want to wait for an order to come in - looking for chemical bonding.. (DEFINITELY didn't plan ahead on this one!) So I got some West Systems locally to continue the job.

So far, it seems like the West Systems bonded OK to the not-fully-cured MAS. I haven't put a lot of stress on it yet, but it sure looks like the epoxy is all one piece.

I've noticed a couple of definite differences between MAS and West:

West is smellier. MAS is relatively innocuous in odor. You should wear a
respirator with either, but with West I can really tell if my respirator is sealed correctly!

West with the "Clear" hardener # 207 (as opposed to the "slow" hardener) is MUCH quicker to cure than MAS. You really need to pay attention to pot life and working time with West. You can take your time more easily with MAS, although if you're in a hurry it can be frustrating waiting days for MAS to cure before proceeding to the next step.

I have some trepidation about mounting my deck using West - I'll have to get everything prepared & do a "dry run" to make sure I can get it all in place before the epoxy starts to set. Not a big problem, but West and 207 hardener does not give as much time to fix goofs as does MAS.

Hope this helps.

Val