Home Depot is now carrying some version of it here in Houston according to my tile guy.
Also, he says it doesn't turn yellow.
Hadn't hurt about the limit on temps - here in Houston, I'd better check that out. Thanks for posting. I will ask tomorrow.

Wouldn't the temp issue be referring to the installation temps? Turn your air conditioning on for that step. The hot water that hits the walls will be hotter than 90 degrees.

Unless I have totally misinterpreted your post :)

enduring - this is for new construction so no ac yet. It's quite hot in the house.

It has been tested on a "bank of black granite outside in Phoenix, Ariz." He said 150 degrees is the limit. Their "most tested product ever" according to my tile guy who has talked to the inventer. My tile guy also also said that whatever the local Home Depot doesn't carry in the color he wants, he can order it from Home Depot.

Thanks lexmomof3. I'm not surprised I miss interpreted your post LOL. Thanks for the help :)

The reason for the heat limit (when installing, not using) is because epoxy grout works with a chemical process. The warmer the temps, the faster the grout sets up. In fact, when I grout with epoxy, I divide the batch into thirds and put part in the freezer, pulling out 1/3 at a time. That gives me more overall working time with the batch.

So if it's over 90 degrees, your tile guy may not be able to get the whole batch spread before it hardens.

Can you buy a window a/c unit and run it in your bathroom temporarily while he's grouting?

Epoxy grout doesn't yellow. In fact, it holds its color when wet, unlike regular grout, which darkens when wet and lightens up when it dries.