COVER STORY A SCREEDY
Mandy Searle, Head of Technical Servic latest solutions for tiling on to anhydrite sc
Anhydrite screeds, also referred to as calcium sulphate or gypsum-based screeds, are now increasingly popular for larger tiling installations. Their use has grown dramatically in the building industry over the last few years because they offer a number of benefits over sand:cement screeds.
The principal advantage is that anhydrite screeds can be laid quicker and easier than traditional sand: cement screeds and are more cost-effective, especially for larger areas. They will self-level and offer minimal shrinkage, making them especially suitable for use with underfloor heating systems, where they will fully encapsulate all pipework. Up to 2,000m² of anhydrite screed can be laid in a single day – compared to 100-150m2
which is
the maximum possible with conventional sand:cement screeds, making them particularly suitable for use on large commercial contracts.
However, there are a number of disadvantages associated with this type of screed, mainly with the extended drying time. Typically, sand:cement screeds should be allowed to dry for a minimum of 21 days before they are able to receive a tiled finish, as per the recommendations contained within BS5385-3:2003. To achieve the required maximum relative humidity (RH) of 75%, the minimum drying times quoted for anhydrite screeds before tiling can commence are one day per mm up to 40mm thickness, with an additional two days per mm thickness above 40mm according to BS8204-7:2003.
REDUCTIONS IN DRYING TIME CAN BE ACHIEVED WITH THE USE OF A
GYPSUM-BASED ADHESIVE.
In ideal drying conditions, therefore, a 40mm thick screed should be allowed to dry for a minimum of 40 days, at 50mm thick the minimum drying time would be 60 days and at 60mm thick a minimum of 80 days drying time would be required before the screed was sufficiently dry to receive a tiled finish. Failure to follow these recommendations and tiling before the screed is sufficiently dry will generally result in adhesion failure at the screed/adhesive interface.
In an attempt to reduce the incidence of failures, Norcros Adhesives worked together with a major national house builder and screed manufacturer, Gypsol, to prepare a generic specification for the industry. Whilst providing a safe method of tiling to anhydrite screeds using cement-
— 12 —
www.tomorrowstileandstone.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32
