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PROPER PR Stephen Boulton, Technical Service Manager for F. Ball and Co. Ltd., gives his advice for achi


Calcium sulphate screeds (also known as anhydrite or gypsum screeds) have become a popular choice of subfloor, particularly in newbuilds, because of the ease and speed with which they can be installed over large areas, less shrinkage and fewer joints required. Although increasingly common, these screeds require a few special considerations when it comes to subfloor preparation.


One of the most common queries that we receive when attending site visits is how best to prepare calcium sulphate screeds before the installation of a floorcovering. Not undertaking certain procedures when working over this type of subfloor is a common cause of floor failure.


22 | SCREEDS, RESINS & COATINGS


High levels of moisture are a particular cause of concern because a waterproof surface membrane tend not be recommended over a damp calcium sulphate screed. With sand/ cement screeds, excess subfloor moisture can be suppressed by applying a waterproof surface membrane. However, calcium sulphate screeds build up strength as they dry. The use of a waterproof surface membrane will trap moisture, impeding strength build-up and reducing the integrity of the screed, resulting in a weak surface. Screeds therefore should be allowed to dry naturally before installing floorcoverings.


PRIOR PREPARATION As with any floorcovering installation, there are a number


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