Our tile contractor planned originally on putting cement board on the floor of our bathroom, which is gypcrete and cannot be screwed into. Gypcrete (I've been told) also can become unstable when exposed to moisture, so adhering the backerboard with thinset (his other plan) does not seem wise either. He put down one coat of redguard, said that was enough, and intends to tile right on top of that. My question is three-fold:
1. Everywhere I've read about Redguard, it says it must have two coats to be effective. He claims one coat is ok. Should I trust his word?
2. Is the floor going to be ok to receive thinset and tile directly over the Redguard?
3. The floor may not be 100% flat, and we are using 12x24" tiles. Should it be leveled first (on top of the Redguard?) so the tile does not end up cracking?
4. Should he be using different thinset/mastic on the floor than he did on the walls?