Why do I have to leave my plaster or screed to ‘cure’ before I start tiling?

During the curing process an ordinary cement mortar (concrete, screed or render undergoes a process known as hydration, which is the reaction between cement and water.  During this process there will be a certain degree of movement in the substrate as a result of shrinkage caused by the hydration reaction as well as evaporation of the water from the mix.  The majority of this reaction occurs within 28 days, and if the tiles are fixed before this hydration has fully taken place, there will be differential movement between the tiles and substrate, resulting in a tile failure (ie the tiles cracking or lifting, or both).  A further factor to be considered is that should the moisture content of the substrate be too high, i.e. higher than 5%,  this could adversely affect the curing of the tile adhesive, weaken the strength of the tile adhesive and/or cause the tiles to delaminate from the substrate.

For this reason good tiling practice dictates that enough time should be left for both the structure itself and the screed or render to stabilise before commencing with the tiling operation.  Please refer to the British Standard for Wall & Floor Tilin (BS5385 1989/90) and SABS 0107-1996 Code of Practice for the Design and Installation of Ceramic Tiling.

TAL’s materials and methods specifications are based on SABS 0107 : 1996, and thus call for a minimum 28 day curing period for new concrete or screeds, and a minimum of 14 days for new render. These curing periods are enough time for the screed or render to hydrate, and the moisture content usually reduces to 5% or lower during the curing periods.

 

 

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