I'm preparing to tile over a wall that is 5/8" thick tongue and grove pine. I have a two part question. #1 - can tile be installed over tongue and grove material? There is about a 3/8" wide by 1/8" deep indentation where each of the boards meet that runs the entire joint. #2 - If I can, can I tile directly over the wood wall with tile mastic or do I need a vapor barrier and sheathing for proper adhesion. BTW, this wall is in a bathroom but will not be exposed to moisture. Thanks