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APPOINTMENTS & NEWS ADF logo_Layout 1 13/09/2016 16:11 Page 2 adf
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NEWS FEATURE
Enjoying the benefi ts of anhydrite screeds
N
ick Bratt, national technical sales manager for tile adhesive manufacturer Palace Chemicals, says that the single issue which he comes across most frequently in queries from architects is the topic of tiling on to anhydrite screeds. Anhydrite (or calcium sulphate) screeds have been available for almost 40 years, and are popular with specifi ers because of the speed with which they can be poured and their sustainability credentials. However they do involve much extended curing times compared to sand:cement screeds. These will have a knock-on effect on project times and budgets. Clearly these are considerations which architects need to be aware of at the building design stage. To achieve the required maximum relative humidity of 75% prior to tiling, the relevant British Standard (BS8204-7:2003) states that the minimum required drying time for anhydrite screeds is one day for each millimetre up to 40 mm thickness, with an additional two days per mm thickness above 40 mm. In ideal drying conditions therefore, a 40 mm thick screed should be allowed to dry for a minimum of 40 days. At 50 mm thick, the minimum drying time would be 60 days and at 60 mm thick, a minimum of 80 days drying time would be required before the screed was suffi ciently dry to receive a tiled fi nish. Failure to follow these recommendations and tiling before the screed is suffi ciently dry will generally result in adhesion failure at the screed/ adhesive interface. This compares with a minimum of 21 days for sand:cement screeds, according to BS5385-3:2003. So why use them? The main advantage is that they can be laid more quickly and easily and are more cost-effective especially for larger areas. They will self-level and offer minimal shrinkage, making them especially suitable for use with underfl oor heating systems, where they will fully encapsulate all pipework. Up to 2,000 m2 of anhydrite screed can be laid in a single day – compared to 100-150 m2 for conventional sand:cement screeds, making them particularly suitable for use on large commercial contracts. Furthermore the latest fast-track systems such as Palace’s own Pro Gyp-Base, are a game changer, since they make it possible to tile with a cement-based adhesive on to anhydrite screeds, which have a relative humidity as high as 95%. This can normally be achieved in just seven days, at which point tiling can commence. This reduces the time required for the overall completion of the fl oor surface by up to ten weeks, which clearly has a very signifi cant impact on timescales and costs on-site. The adoption of one of these new systems will allow contractors to derive all the benefi ts of rapid and easy pouring of an anhydrite screed, without involving delays on the job caused by having to wait for an extended drying period.
Supplied by Nick Bratt, national technical sales manager for Palace Chemicals
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