Protecting a water-sensitive substrate

Tiles are often specified for areas that are likely to be subjected to high humidity or become wet such as kitchens, bathrooms and showers. Whilst the tiles themselves are unaffected by water it is very difficult to ensure a complete seal at the grout joints. The tiling layer should not be considered to be a waterproofing layer, and the use of a tanking kit is required to waterproof the substrate.

Common issues and queries you can face


Some tiling substrates are affected by water

Plaster will lose nearly all of its cohesive strength if it gets wet for any extended period. Plasterboard has a paper face which also loses strength when wet.


Cement-based grouts are not impervious to water

Cement-based grouts, whilst being unaffected by water once set, are porous and will therefore allow water to seep through. If the joint is not completely filled with grout then of course this will allow water through.


Cement-based grouts are vulnerable to erosion

Normal wear and tear from traffic and cleaning will erode the grout over time. The action of various chemicals, such as cleaning liquids can gradually weaken the grout. Either or both of these actions can reduce the ability of the grout joint to resist the passage of water.

Movement cracks in grout joints

Movement cracks

Grout joints in corners between tiled surfaces and at junctions between dissimilar backgrounds should be filled with a flexible sealant to allow some movement between surfaces. These critical joints are often filled with the same grout used for the rest of the area. The grout will almost certainly crack in time allowing water through.