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Contractors that automatically specify a straightforward sand and cement mix for their floor screeds may be missing a trick, as there are some new materials on the market that have significant advantages over the usual.

Gyvlon from Lafarge is one such material. Andy Vincent, Gyvlon鈥檚 managing director, says: 鈥淚t looks and behaves like cement but it is very resistant to shrinking, curling and cracking. It鈥檚 a better product.鈥�

He says Gyvlon鈥檚 stability during curing is caused by the presence of the binder 鈥渟ynthetic anhydrite鈥�, which is a form of gypsum and a by-product of hydroflouric acid production. The anhydrite prevents the floor screed from shrinking and cracking while it dries. Vincent explains: 鈥淲hen water is added to cement it shrinks as it cures, but Gyvlon is stable and can even expand a little. You can control shrinkage in cement but it is expensive. Cement also tends to be more sensitive to small changes in mixing or site conditions.鈥�

Shrinkage can be a particular problem for cement screeds laid thickly, says Vincent, as the differential rate of drying at the top and bottom can result in curling.

Gyvlon has other attractions, too. It requires far fewer construction joints than normal screeds, is self-compacting, requires no reinforcement, can be applied rapidly and withstands foot traffic within 48 hours. It also has environmental benefits over its rivals (see box below).

Gyvlon is pump-applied and can rapidly form large areas of self-levelling floor screed ready to take thin floor coverings, tiles, and carpets and other specialist finishes. Vincent says that the price of screed is competitive with sand and cement mixes, especially for areas greater than 500 m2. Its main market until now has been for floor areas of at least this size, although it is being increasingly used for smaller areas, such as houses.

The speed of application is another benefit to applicators, according to Vincent. Lafarge Gyvlon says 500-1000 m2 can be pumped per day and Vincent adds that 3200 m2 has been achieved. He has one warning, though. Vincent says Gyvlon has to be programmed into the construction schedule. Unlike traditional sand and cement screeds, subcontractors can not fit in around other trades by applying small amounts at a time.

One property of the material that will interest architects and structural engineers is that the screed can be thinner than traditional materials, which reduces the weight of the subfloor. In floating floor construction, Gyvlon says, a minimum thickness of only 35 mm is required for commercial buildings and 30 mm for domestic buildings. For unbonded floor construction, this minimum is 30 mm. by contrast, with sand and cement, the typical thicknesses are 65 mm for floating floors and 50 mm for unbonded floors. Another advantage, which may appeal to contractors, is that no fibre reinforcement is required.

Gyvlon has a market share of 5/6% but with sales growing at 30-40% a year, that figure is sure to rise. Expect to see more Gyvlon being specified for smaller projects. It has a premium of 5-10% in projects smaller than 500 m2 but Vincent says it is increasingly being specified by housebuilders who are impressed with its finish and the fact that it can be walked on two days after application.

Lafarge has high hopes that Gyvlon will take off in the housebuilding sector 鈥� it recently introduced 25 kg bags of the screed. By adding water on site, the contractor has the flexibility of using Gyvlon as and when it is required to suit the schedule.