Tile adhesive manufacturer Palace Chemicals offers a RIBA-approved CPD entitled: Successful specification of wall & floor tiling and how to avoid common failures. Here Nick Bratt, National Technical Sales Manager, outlines some key points regarding substrates, which will help specifiers avoid problems.
Success or failure of a tiling project will in part be determined by procedures and practices employed by the tile fixer on-site. However, decisions taken at the specification stage will also have a critical impact on the ultimate success of the project.
One of the most important aspects is to correctly specify the substrate on to which tiles are going to be fixed. For example, timber is unsuitable for direct tiling, as it can distort and create excessive movement beneath the tiled finish, leading to cracks, loose tiles and debonding.
If a timber substrate has to be used, a suitable waterproofing/tanking membrane prior to tiling should be installed. Since the publication of British Standard BS 5385 Part 1: 2018, plywood has not been considered a suitable background for direct wall tiling.
The latest revision to the British Standard, BS 5385 Part 3: 2024 stresses the importance of using appropriate materials for direct tiling, and states that timber boards are no longer recommended for direct floor tiling.
In addition to providing enhanced adhesion with greater weight loadings than timber, a bespoke backer board will also form a waterproof and well-insulated substrate to which tiling can be applied directly.
Plaster and plasterboard, which are very common wall substrates, can also pose issues. For example, both are sensitive to moisture and should not be used in wet areas.
Floor tiling is often applied to a screeded surface, which can be either a cement:sand screed or an anhydrite screed. The main problems occurring when tiling to cement:sand screeds relate to shrinkage during the curing process. Tiling on to a screed that is not cured can lead to lifting of tiles. The recommended solution for tiling to green screeds is to use a suitable anti-fracture membrane.
If tiling on to anhydrite screeds, one of three different solutions can be implemented to avoid system failure. Either typically wait up to 80 days, in the case of a 60mm screed, and at 75% RH use varying dilutions of SBR primer and cement-based adhesive, or at 85% RH use a gypsum-based adhesive, which enables a reduction in drying time or, and this is the best solution, specify a fast-track proprietary anhydrite screed preparation system. This can be applied when the relative humidity of the screed is as high as 95% – normally achieved within seven days. In addition to eliminating ettringite formation, this speeding up of the process has a major benefit with regard to project planning and schedules.