Impervious tiles or substrate

When tiling an area that is already tiled or painted, it is often necessary to invest considerable time in stripping and then repairing the substrate. In certain situations it is more convenient to tile over the existing layer. However, this requires careful consideration and an adhesive with exceptional properties.

Common issues and queries you can face

Not sticking to smooth surfaces

Standard cement-based tile adhesives won’t stick to a completely smooth surface.

Mechanical keying action

  • Standard cement-based adhesives rely on a mechanical keying action to bond onto the substrate. The wet cement engages physically with small irregularities, pores etc in the surface and uses this to form a strong bond.

Poor key onto tile face

  • When the surface is very smooth this grip is much weaker resulting in tiles de-bonding.
  • Existing ceramic tiles, existing vinyl tiles and paint can all present a surface that is closed in this way.
  • The back of very low porosity tiles, such as porcelain, is also closed.

Largely impervious surfaces

These types of surfaces are largely impervious to water and this results in a longer time delay before the water from the adhesive can escape the system.

Over-tiled wall

  • Ready-mixed adhesives are dispersions of polymers and inert fillers in water and do not gain strength until the majority of the water has dried out. With large tiles on impervious surfaces, this can take weeks.
  • At lower temperatures, even standard cement-based products can take several days to set and dry.
  • The other complication from slow extended drying is that if the joints are grouted before the drying is complete, the water will be trapped. As it subsequently permeates through the grout it will bring dissolved salts from the adhesive or grout and cause a white deposit on the surface of the grout, known as efflorescence. This can happen sometimes anyway, but the chances are increased the more water is trapped.


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