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Achieving a suitable adhesive bed

The adhesive bed performs a number of functions: it sticks the tile to the surface; it absorbs differential movement between the substrate and the tiles; it protects the substrate from water; it absorbs deflections; it enables the tiler to adjust the height of each tile; it accommodates limited errors in the substrate.

There are a number of ways that an improper adhesive bed can cause problems in the life of the installation, as detailed below.

Problem

Voids behind the tiles allow access to any water that penetrates the grout

This can cause a damp, musty smell in showers. Any water leaks are made worse by having channels available for water to run through. Externally, any trapped water can freeze and the associated expansion can push tiles off.

Voids leave floors susceptible to point loads

Ceramic tiles are inherently brittle and therefore any area of the tile that is not fully supported is vulnerable when subjected to a localised load. Examples could be: a chair leg, something being dropped, or any heavy item on small feet such as a kitchen appliance.

The thickness of the adhesive bed is also important

If the adhesive bed is too thin, a cement-based adhesive may dry out very quickly and not gain strength and structural integrity. In the case of floors where some movement is expected, the adhesive is required to give, and its ability to do this is severely limited if it is applied too thinly.

Variations in the adhesive bed will show through some tiles

Some tiles and natural stones (e.g. limestone and marble) will show an adhesive shadow on the face of the tile, where the adhesive is in contact with the tile. Voids behind the tile may be visible from the front of the tile. Areas where there is no contact between the tile and the adhesive bed will not be bonded. A 50% contact will therefore result in only 50% of the overall bond strength across the tile.

Solution

Use a suitable notched trowel

Using the appropriate trowel helps to ensure that an even layer of adhesive is achieved and leaves ribs that allow for adjustment of the tile height. For wet areas, exterior areas and all floors, it is necessary to achieve a solid bed of adhesive under the tile. The adhesive should be applied in a consistent manner using the correct type of trowel. When applying on walls, the adhesive should be applied in horizontal parallel strokes for dry areas, and vertical strokes for wet areas. Do not apply in swirls as this causes air pockets to form. The tile should be pressed into place with a twisting and/or sliding action to ensure a good contact with the adhesive. It is recommended that during tile fixing, an occasional tile is lifted back up, to verify that the desired contact is being achieved.

  • Walls in exterior or interior wet areas : Notch size 8 mm x 8 mm Tooth width:8 mm
  • Wall tiles in interior dry areas : Notch size 6 mm x 6 mm Tooth width:6 mm
  • Mosaic tiles Notch size: 6 mm x 6 mm Tooth width: 6 mm

Large tiles:

If the tiles are very large or have large studs or ribs on the back it may be necessary to back-butter the tile as well as spreading the adhesive on the substrate.

Floors:

  • Notch size: 10 x 10 x 10 mm notched trowel
  • Solid finished bed: 3-6 mm deep

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.set Ceramic S

A cement-based tile adhesive for small format Ceramic tiles (smaller than or equal to 420 x 420 mm)

weber.set Ceramic L

A cement-based tile adhesive for large format Ceramic tiles (larger than 420 x 420 mm)

weber.set Ceramic White

A white cement-based tile adhesive for Ceramic tiles.

weber.fix Super-flex

High-strength, ready-mixed, thin-bed paste tile adhesive.