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Tiling onto wood

Timber floors and ceramic tiles are not natural bedfellows – tiles are inherently rigid and brittle whereas timber floors are flexible. There are many types of wooden floors but in principle the challenges that they present to the tiler are all the result of this mismatch. There are a number of contributing sources of movement in timber floors which need to be considered when fixing ceramic tiles or natural stones.

Problem

General deflection due to the applied load

The floor will deflect according to the load applied and the stiffness of the structure (joint 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.

Wooden floor to tile over

Localised movement at unsupported board joints

Creaking in certain places as you walk on the floor

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.

Temperature related expansion and contraction

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).

Moisture/humidity related expansion and contraction

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).

Solution

Solution 1: Overboard with plywood or tile backer-board

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, helps prevent localised movement, and if a water-resistant tile backer board is used, it virtually eliminates moisture related movement. Screwing the boards down also helps prevent any pull out of fixings.

Solution 2: Tile directly onto tongue and groove boards or sheets

It is possible to tile directly onto tongued and grooved wooden floors by using a highly polymer-modified 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 1).

Solution 3: Tile directly onto non tongue and groove sheets

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 40 x 40 cm) weber.set Quick Set 6 is adequately flexible.

Solution with the following weber products

Solution 1

weber.set Quick Set 6

A high strength, quick setting cement-based tile adhesive for all tiles.