QUESTION

Expansions Joints - Which factor would have the greatest influence, lack of an expansion joint (longest run is 38') or lack of moisture proof membrane beween the plywood and the tile? The house is 9 yrs old - why no problems until now - initiated use of a humidifier in the basement last summer or the cold snaps in Jan & Feb (55F to -7)?

ANSWER

ANSWER - Lack of expansion joints is number one enemy in our industry. Should be placed at least within every 25 feet in all directions for interior applications, around all perimeters of walls and columns, and at any transition of planes or transitions into other substrates and surface materials. If you don't have this doesn't mean you will have problems, only that you are more likely to have a problem.

A vapor or waterproof membrane between the plywood and ceramic tile isn't necessary, unless you are in a bathroom or another area that can get wet. If moisture comes from under wood, then wood can swell and warp causing stress on ceramic tile, and having a membrane won't prevent this and could make it worst. Of course, shouldn't have moisture coming up from under the wood. Good Luck!
ANSWER - Lack of expansion joints is number one enemy in our industry. Should be placed at least within every 25 feet in all directions for interior applications, around all perimeters of walls and columns, and at any transition of planes or transitions into other substrates and surface materials. If you don't have this doesn't mean you will have problems, only that you are more likely to have a problem.

A vapor or waterproof membrane between the plywood and ceramic tile isn't necessary, unless you are in a bathroom or another area that can get wet. If moisture comes from under wood, then wood can swell and warp causing stress on ceramic tile, and having a membrane won't prevent this and could make it worst. Of course, shouldn't have moisture coming up from under the wood. Good Luck!