QUESTION

Can I install tile over Wood? - I am building a house and putting tile down in a number of areas over wood subfloors.

For elevation reasons I would like to "glue" the tile down. BUt I am told by my tile contractor that gluing tile to wood will create cracks eventually as wood expands and contracts. Is there an adhesive such as a silicon adhesive or contact adhesive that will work? ANd then use some kind of flexible grout? Will a mortar bed not also expand and contract? If I must use mortar how thin can I go to get proper adhesion?

ANSWER

ANSWER - It is possible to bond tile directly to wood, if the floor assembly is properly constructed to limit deflection, and if the floor will not be subjected to any prolong water or moisture vapor.  You do need joists 16: o.c. and two layers of plywood with 19/32" thick minimum as subfloor and 15/32" minimum for wood underlayment.  You can use an ANSI A119.11 thin-set adhesive to bond the tile to the wood.

Wood is not the best substrate.  It would be better to apply a 1/4" or 1/2" thick cementitious backer board over a minimum 19/32" exterior-glue tongue and groove plywood subfloor.  Make sure there isn't excessive deflection.  You can also use a cementitious self-leveling underlayment instead of the backer board.  Mortar beds are the best if you have the room for them and if the floor can withstand the added weight, because they provide a more structurally stable surface.  Although the other methods work well too if done correctly.