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 (creak)

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.

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. Overboarded 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, 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.

Stage 1: Assess and prepare the floor

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. Brace any areas that need extra support with noggings between the joists. Any defective boards should be cut out and replaced. Existing boards should be screwed down to joists with two screws at each end and another two wherever they cross joists.

Stage 2: Fix the over-boarding

For small floors with no noticeable deflection 9mm WBP plywood can be used for over-boarding. If there is some limited deflection, a minimum of 15mm WBP plywood or equivalent tile backer board should be used. Prime the back and edges of plywood with weber PR360. Lay the boards so that the joints do not coincide with the joints in the existing timber and leave gaps of approximately 2mm between boards and 5mm at the perimeter for expansion. Screw the plywood or tile backer board to the floorboards every 200 - 300mm using corrosion resistant screws. Fill the gaps between boards and the perimeter with weber.joint silicone sealant. If there is still noticeable movement in the floor, another layer of plywood or tile backer board may be needed.

Stage 3: Fix the tiles

Fix the tiles into a solid bed of weber.set rapid SPF at least 3mm thick. Leave joints at least 3mm wide for grouting and make provisions for movement.

Stage 4: Grout

Leave the adhesive to set for 2 to 3 hours. Fill the joints between tiles with weber.joint wide flex or weber.joint pro. Use weber.joint silicone sealant to fill the perimeter movement joints.

Solution 2. Tile directly onto tongued and grooved boards or sheets

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 400mm square, over boarding is recommended.

Stage 1: Assess and prepare the floor

Make sure that the floor will be capable of supporting the expected load with minimal deflection. It must be stable, well supported, ventilated underneath and level.

Ensure that each board is effectively supported by its adjacent boards without localised movement. Replace any defective boards and insert noggings between the joists if necessary. Screw the boards to the joists using two screws per board at every joist and prime with weber PR360.

Stage 2: Fix the tiles

Fix the tiles into a solid bed of weber.set rapid plus & weber AD250 at least 5mm thick. It may be necessary to back butter the tile to achieve this.

Leave joints at least 3mm wide for grouting and make adequate provision for movement (especially around the perimeter and dividing large areas into bays).

Stage 3: Grout

Leave weber.set rapid plus & weber AD250 to set for 2 or 3 hours. Fill the joints between the tiles with weber.joint wide flex or weber.joint pro. Use weber.joint silicone sealant to fill the perimeter movement joints.

Solution 3. Tile directly onto plywood

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 400mm) weber.set rapid SPF is adequately flexible. For larger tiles use weber.set rapid plus & weber AD250.

Stage 1: Assess and prepare the floor

Make sure that the floor will be capable of supporting the expected load with minimal deflection. It must be stable, well supported, ventilated underneath and level.

The sheets should be of exterior grade plywood and at least 18mm thick. 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 noggings between the joists beneath any unsupported sheet edges. Prime the back and edges of plywood with weber PR360.

Screw the sheets to the joists/noggings every 200 - 300mm, leaving 2mm to allow for expansion. Fill the gaps with weber.joint silicone sealant to prevent them being filled with tile adhesive when fixing the tiles.

Stage 2: Fix the tiles

Fix the tiles into a solid bed of weber.set rapid SPF at least 5mm thick. It may be necessary to back butter the tile to achieve this.

Leave joints at least 3mm wide for grouting and make adequate provision for movement (especially around the perimeter and dividing large areas into bays).

Stage 3: Grout

Leave weber.set rapid SPF to set for 2 or 3 hours. Fill the joints between the tiles with weber.joint wide flex or weber.joint pro. Use weber.joint silicone sealant to fill the perimeter movement joints.