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Surface Prep Is Key To A Good Performance

Barry Hodges, technical Manager, Mapei UK, explains why proper surface preparation is key to performance: 
THE importance of correct subfloor preparation cannot be emphasised strongly enough. Performance of any applied preparatory materials and, of course, subsequent floorcoverings are wholly dependent upon the process.
The correct method of preparation is dictated by the nature of the substrate and it is vital that you establish its exact composition. There are numerous substrates you may come across, including sand:cement screed, power floated concrete, anhydrite-based screed and proprietary fast drying screeds, some of which incorporate hydraulic binders.
All subfloors should be tested using the approved method (as detailed within BS8203 Code of Practice for the Installation of Resilient Floorcoverings), to ensure that the moisture content is below the required level to receive the chosen adhesive and resilient floor covering.
These levels are 75%RH or less for sand:cement screeds and power floated concrete and 0.5%w/w for anhydrite based screeds.
Methods for testing and the required moisture levels for any proprietary screeds should be sought from the relevant manufacturer.
Once the moisture tests have been carried out, and the results have confirmed that they are within the requirements for the substrate tested, preparation can commence.
Sand:cement screeds should be mechanically abraded to remove surface laitance and any other contamination that may be present.
It is then important that the subfloor is vacuumed to remove all dust and debris. An acrylic water-based primer should then be applied to the subfloor, prior to the application of a cement-based smoothing/levelling compound (either a water mix or a two-part latex mix), ensuring a minimum thickness of 3mm is achieved.
Power floated concrete has a highly polished mirror-like surface and must also be mechanically abraded. This abrasion is required to remove any surface contamination, along with any curing agents used, and to open up the top surface.
Once abraded, the subfloor must be thoroughly vacuumed and primed using an acrylic water-based primer, prior to the application of a cement-based smoothing/levelling compound (either a water mix or a two-part latex mix), ensuring a thickness of at least 3mm is achieved.
Similarly, anhydrite screeds must be mechanically abraded to remove any surface laitance that has formed during the drying process.
The surface should then, once again, be thoroughly vacuumed. If a cement-based smoothing/levelling compound is being used, the anhydrite screed must be primed using an acrylic water-based primer; two applications may be required, depending on porosity.
If the moisture tests carried out on either sand:cement screeds or power floated concrete indicate that the subfloor has not dried to the required level, a surface-applied damp proof membrane can be installed to control residual or construction moisture.
However, anhydrite screeds are not suitable to receive surface-applied damp proof membranes and should be left to dry naturally, until the required moisture level is reached.
During refurbishment works to existing subfloors, it is once again imperative that the nature of a subfloor is identified, before selecting any preparatory materials.
All existing preparatory and deleterious material should also be removed, to expose the surface.

This article has been reproduced from the Contract Flooring Journal website. You can find them at