Problem
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 floor 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.
1. General deflection due to the applied load (bounce).
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.
2. Localised movement at unsupported board joints.
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 groove sof each board beneath.
3. 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).
4. 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 1
Tiling onto timber or non-tongue and groove floorboards and chipboard.
Timber and non-tongue and groove floorboards and chipboard are usually subject to large amounts of deflection/movement, and therefore cannot be tiled onto with even the most flexible of tile adhesives. This means you will need to strengthen the substrate first with either a levelling compound, tile backer board or plywood. Use our guide below to learn how to tile onto timber floors.
Stage 1. Increase rigidity and strengthen the substrate.
You will first need to increase the rigidity of your substrate either by covering with a 10mm layer of Weberfloor Flex, 6mm tile backer board, or 15mm plywood. Strengthening the substrate will decrease the amount of movement associated with timber and non-tongue and groove floorboards and chipboard.
Stage 2. Fix tiles with a suitable flexible tile adhesive.
Fix tiles with a 3mm bed of improved flexible tile adhesive (S1) — such as Weberset SPF or Weberset Rapid SPF — and leave joints of at least 3mm wide for grouting and make provisions for movement. If you are fixing tiles above 400mm by 400mm in size, or heavier tiles made of stone, quartz or terrazzo, you will require an ultra-flexible tile adhesive (S2) such as Weberset Pro Lite Rapid.
Stage 3. Finish with grout and silicone.
Leave tile adhesive to set and fill joints with a flexible floor tile grout. Finish the job by sealing the perimeter movement joints with silicone sealant.
Solution 2
Tiling onto tongue and groove floorboards and chipboard.
It is possible to tile directly onto tongue and groove wooden floors, but the high amounts of deflection/movement will mean that an ultra-flexible (S2) tile adhesive is required. Alternatively, another option is to strengthen the substrate with either a layer of floor screed or by overboarding with plywood/tile backer board, and then using an improved flexible (S1) tile adhesive.
Stage 1. Determine if you need to increase rigidity of the substrate.
Depending on the amount of movement and deflection, you may need to strengthen the substrate before tiling. You can do this either by covering with a 10mm layer of weberfloor flex, 6mm tile backer board, or 15mm plywood. Use our guide on strengthening a wooden floor for tiling to do this. Strengthening the substrate will decrease the amount of movement associated with timber and non-tongue and groove floorboards and chipboard.
Stage 2. Fix tiles with a suitable flexible tile adhesive.
If you strengthened the substrate with tile backer board, plywood or with a layer of weberfloor flex, you will now need to fix tiles with a 3mm bed of improved flexible tile adhesive (S1) — such as Weberset SPF or Weberset Rapid SPF — and leave joints of at least 3mm wide for grouting and make provisions for movement. You will require an ultra-flexible tile adhesive (S2) such as weberset pro lite – rapid if you are either:
- Tiling directly onto the tongue and groove floorboards or chipboard
- Fixing tiles above 400mm by 400mm in size
- Using heavier tiles made of stone, quartz or terrazzo
Stage 3. Finish with grout and silicone.
Leave tile adhesive to set and fill joints with a flexible floor tile grout. Finish the job by sealing the perimeter movement joints with silicone sealant.
Solution 3
Tiling directly onto plywood.
Can you tile on plywood? Yes, but various considerations need to be made first.
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 (no larger than 400mm by 400mm) an improved flexible (S1) tile adhesive is suitable. For larger or heavier tiles, you will require an ultra-flexible (S2) tile adhesive.
Stage 1. Assess and prepare the surface.
Make sure the floor will be capable of supporting the expected load with minimal deflection. It must be stable, well supported, ventilated underneath and level. The thickness of the plywood needs to be at least 18mm and of exterior grade. It may be necessary to increase the thickness if heavy loads are anticipated or if the joists are spaced more widely than normal. Replace any defective sheets and fit noggins between the joists beneath any unsupported sheet edges. Prime the back and edges of plywood. Screw the sheets to the joists/noggins every 200-300mm, leaving 2mm to allow for expansion. Fill the gaps with silicone sealant to prevent them being filled with tile adhesive when fixing the tiles.
Stage 2. Lay tiles with a suitable flexible tile adhesive.
Lay tiles with a 3mm bed of improved flexible tile adhesive (S1) — such as Weberset SPF or Weberset Rapid SPF — and leave joints of at least 3mm wide for grouting and make provisions for movement. If you are tiling on a plywood floor with tiles above 400mm by 400mm in size, or heavier tiles made of stone (quartz or terrazzo), you will require an ultra-flexible tile adhesive (S2) such as Weberset Pro Lite – Rapid.
Stage 3. Finish with grout and silicone.
Leave tile adhesive to set and fill joints with a flexible floor tile grout. Finish the job by sealing the perimeter movement joints with silicone sealant.
