I should have made it more obvious........ chuckle

The drug store isopropyl alcohol is only 70% isopropyl alcohol. What do you guess you're thinning with when you use it? So you're actually already thinning with water. And therein lies the answer..........

chuckle.....

I said that you can thin with water, and darn if you can't. You could thin with mud if you wanted to. Or motor oil. chuckle.... (but I wouldn't if I were you) If you're smart enough, it'll be obvious to you whether or not you should thin with water or mud and whether or not it'll make the epoxy stronger. But to save misunderstanding, don't thin with water or things that have water in them unless the strength of your epoxy isn't really important.

None of us are setup to do a quality test of the resulting strength of our epoxy, nor do any of us do any kind of test other than maybe a crash test later. Sure, some look at and touch the epoxy later on after application. But painting epoxy on a firewall isn't exactly an application that requires all the strength of the epoxy. And everybody forgets that whatever is trapped by the cured epoxy is adding weight.

Do yourself a favor and do a little test. Mix up a batch of epoxy in a little cup. Weigh it. Thin it with whatever you wish. Weigh it right away. Let it cure. Weigh it again.

Do another little test. Mix up some epoxy. Spread some of it on a balsa sheet. Now thin the rest with whatever you wish. Spread it on the other end of that balsa sheet. Let them cure. Now break the sheet where the two epoxy spreads are.

It's amazing how simple and easy some questions are answered for ourselves.