According to the tile bible by M. Bryne I do but what I don't
understand is this: If water gets through the tiles/grount and then
penetrates the cement board then wouldn't it be better to let it
essentially evaporate into the air void between the walls rather than
trap it? Especially if you have the vapor barrier sealed off and the
bottom of the tiles is caulked etc. where is the water going to go
except get trapped. Could someone explain this please?