# Fred # wrote:

Not being a wet area, cement board may not be necessary,
but every homeowner/handyman/know-it-all thinks it is.


If cement board is not required, what do you use as an underlayment? Or do
you just lay the tile directly under the subfloor without any underlayment?

The completed floor must be at least 1 1/4" thick
to be tiled properly. Often a homeowner will lay
tile directly over the sole 3/4" plywood floor.
There must be no flexing so everything must be
glued/screwed tightly or the tile will pop loose or
crack.

That said, assuming the original floor was typical
3/4" construction, the homeowner could glue
and screw 1/2" exterior grade (cdx) plywood
to the 3/4" floor and end up with the required
1 1/4" floor needed to receive tile.

If the floor is not a bathroom, and is always
temperature controlled, plywood is a fine
subflooring material (exterior grade only).
The principle reason to use cementboard is
that it's dimensionally stable- it won't expand
and contract so is more suitable in a home
that might get temperature extremes like up
north, particularly if the home is allowed
to get cold inside, then heated up in the day.

My experience is in SW Florida so the only
expansion/contraction issues I deal with are
exterior applications where it can be in the
40's at night and go up to the 80's in the day.

thetiler