Tiling onto wood

The floor will deflect according to the load applied and the stiffness of the structure ( joist size, spacing etc).

If the adhesive is not flexible or laid thick enough to absorb the amount of movement, the tiles will either delaminate or crack. Large tiles will exacerbate the deflection across each tile's width.

Any inadequately supported joint will cause a highly localised movement which will crack the tile.

Joints may be supported by joists, noggings, or each other's tongues and grooves.

Wood expands and contracts with changes in ambient temperature at a different rate to mortars, ceramics and stones.

As a further complication, timber expands much more across the grain than it does along the grain (this is not really a factor with manufactured boards such as plywood).

Wood swells if it gets wet even with changes in atmospheric humidity.

This can be a problem in potentially wet areas such as showers and bathrooms and also if the wood is not dry when installed (e.g. if it has been kept outside).

The most secure system for tiling wooden floors is to screw fix another layer of boarding over the top of the original timber. This increases the rigidity of the floor, prevents localised movement and if a water-resistant tile backer board is used virtually eliminates moisture-related movement. Screwing the boards down also helps prevent any pullout of fixings.

It is possible to tile directly onto tongued and grooved wooden floors by using a highly polymer-modified 2-part adhesive, providing that the floor is rigid enough and the tongued and grooved joints provide effective support. If the tiles are larger than approximately 400 mm square, over-boarding is recommended (see Solution 7.1).

If the floor consists of sheets that do not support each other, it is necessary to ensure that each edge is fully supported underneath. If the tiles are small (not more than 400 x 400 mm) weber.set rapid SPF is adequately flexible. For larger tiles use either weber.set rapid flex or weber.set WF21.