However you re not out of the woods.
Subfloor material for ceramic tile.
Underlayment is the material placed on top of the subfloor that assists in the installation of the tile or other type of flooring.
A plywood subfloor must be structurally sound and able to support the installation.
It will break or dislodge if the surface bends under the load.
Tile floors are heavy and tile is a hard material.
For ceramic tile the tile council recommends using joists that are 16 inches on center a 3 4 inch thick plywood subfloor and a 1 2 inch thick cement backer board or concrete slab.
Laying tile on plywood.
When installing a ceramic tile floor on a concrete subfloor you don t have to worry about flexing as long as the concrete slab is at least 1 1 8 inch thick which most slabs are.
It sounds like your joists are well within the acceptable limits of l 300 so your main concern is the deflection of the subfloor between joists.
With ceramic tile you also need to limit the deflection between joists which is a function of the subfloor thickness and how it is installed.
Materials such as vinyl and carpeting are flexible enough to tolerate engineered floor truss systems with larger joist spacings such as 24 inches on center.
Check for dips in the floor by sliding a 4 foot to 6 foot straight edge in different directions all around the room.
Concrete expands and contracts and that type of movement can also crack the tiles and the grout.
2 prepare a wood subfloor for tile a successful tile installation project requires a level surface.