Check the solids content in any epoxy you are going to put down. Most of them are not 100% solids - far from it, most are less than 50% solids. This equates to far less life of the product. You want 100% epoxy with a clear poly coat on top - this provides the best surface and longevity. (Well, using poly all the way is even better but costs $$$).
I did my own - a 2 car extended garage. I took me about 4 days total as I did one side and then the other. Turned out fantastic! I did a lot of research on garage floor epoxy products, and epoxy-coat kept coming up with great reviews from trade journals as well as customers.
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