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Tiling onto floating floors

Floating floors is a term used for a floor that is not attached to a rigid substrate. Generally this will be a tongued and grooved wooden board above an acoustic or insulation material. Floating floors are used to improve floor insulation and or to reduce noise transmission. Normal wooden floors flex when loaded but this movement is even greater on a floating floor as the boards are not supported by joints.

Problem

Deflection

Causes bending of the floor

As a floating floor is not supported by joints, any applied load creates significant movement over a big area. This can be felt as bounce in the floor when it is walked across. As the applied load increases so does the severity of movement.

The edges of a floating floor are even more susceptible to exaggerated movement as they are not supported and any applied load is spread over a smaller area. If the adhesive used to fix the tiles is not flexible or 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.

Unsupported joints

Causes cracks in tiles over joints

If a joint between wooden boards of a floating floor is not correctly located or fixed, it will be susceptible to highly localised movement which will crack the tile along the joint. If the boards of a floating floor are not tongue and grooved, they are not suitable for tiling.

Columns

Created by nails fixing overboards to floating floor. The loose nail pushes up against the tile and cracks it from behind

When a floating floor is over-boarded to add rigidity, the extra board has to be securely attached to the original boards. If nails are used, the constant movement of the floor can cause them to work loose, press on the underside of the tile and cause cracks. If the screws/nails used are too long they can bottom out on a rigid surface under the floating floor and create a column, over which tiles will crack.

Solution

Overboard with plywood or tile backer-board

1: Preparation

Verify that the extra height from the over-boarding can be accommodated and that the floor is capable of supporting the expected load. All tongued and grooved boards should be glued together securely and wedged around the edges until dry.

2: Fix the over-boarding

Use plywood at least 15 mm thick. Lay the boards so that the joints do not coincide with joints in the existing timber and leave slight gaps between boards to allow for expansion. Screw the boards at 200 to 300 mm intervals. Leave a movement joint around the perimeter for expansion.

3: Fixing the tiles

Fix the tiles into a minimum 5 mm solid bed of weber.set Ultra-flex. Leave joints at least 3 mm wide for grouting and make adequate provision for movement (around the perimeter) and dividing large areas into bays. Leave the adhesive to set and then grout the tiles with weber.grout Tile Grout WB33 mixed with weber.ad Bond-it WB183 only.

Use a suitable silicon or polysulphide soft joint for perimeter joints.

Solution with the following weber products

Solution 1

weber.set Ultra-flex

A highly deformable, fast setting, high strength cement-based tile adhesive for all types of tiles.

weber.grout Tile Grout WB33

A cement-based grout for tile joints on walls and floors. (2 - 8 mm joint width)

weber.ad Bond-It WB183

A latex-based liquid additive specifically formulated for use with Weber’s cement-based adhesives and grouts.