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.
Proper subfloor for tile.
Preparing a subfloor is an essential step for installing floor tile it provides a level surface that will allow the tiles to properly stay in place.
3 check before installation.
A plywood subfloor must be structurally sound and able to support the installation.
The subfloor must be free of moisture damage including rot and sponginess and must be securely fastened to the joists and squeak free don t lay tiles on a concrete slab with cracks that appear to be spreading or irregularities that prevent you from leveling it.
Once you determine the subfloor is the proper thickness check that the subfloor is installed properly with no issues that could affect your installation.
Cement backer board can provide a solid flat surface to install tiles on if you have a wood subfloor.
This guide will show you how to prepare your subfloor for a tile installation project to ensure that it s fit to support ceramic or porcelain tile.
Subfloor panels and fasteners should be properly placed according the panel manufacturer s specifications.
Proper preparation of the subfloor is critical to the success of your ceramic tile installation.
It will break or dislodge if the surface bends under the load.
Because of issues of moisture movement and adhesion ceramic tile will work well with certain types of subfloor underlayment systems and can go dramatically wrong with other subfloor materials.
For this reason ceramic and porcelain tile floors can be considered somewhat delicate despite the inherent strength of the material.
How to prep a plywood subfloor for tile by official fine homebuilding post for residential use one form of underlayment the tile council of north america s handbook allows is plywood over joists that are 16 in.
A tight unmoving bond between mortar and subfloor causes cracking.
The dry product is mixed with water to a liquid consistency and poured on.
In addition uncoupling tile membranes prevent moisture from infiltrating surfaces below.
Wood building materials contract and expand at different rates from natural humidity and exposure.
It uncouples or releases the bond between plywood and tile mortar allowing each surface to move independently of each other.
Pourable self leveling products help to flatten and level a wood subfloor or a concrete slab before the tile is installed.
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.