Hello I am remodeling my bathroom (circa 1935). I am wondering if I can use modified thinset 1/4 inch deep to bring the thickness of the gypsum plaster to the same thickness as the mud bed plaster that is below it which had tile on it. I am putting new tile on the bathroom walls (3x6). This is plaster on brick exterior walls. I want to tile about 22 inches higher than what was there and the gypsum plaster is about a quarter inch thinner that the mud bed where the old tile was. The plaster is painted and in good condition with out peeling or crumbling. FYI this is not in a wet area I took it to stud and used durarock with a membrane in the shower.