FLOORING AND SCREEDING
The drying game
The amount of screed that can be installed in a set period is only half the story. If you include drying times you may well find that what you think is fast track is anything but. Adrian JG Marsh finds out how pressure on site is damaging floor screeding. “How often have I heard a site manager say we’ve had nothing on this floor; only for him to turn around and see a machine driving towards us on the newly screeded floor!” says Dave Taylor of screeding contractors Roseville Plastering. The ability to lay large areas of floor screed in a short time may initially be considered ‘fasttrack’. However some clients seem unaware of the pitfalls of using a floor before it’s ready and the impact on the resultant integrity of floors, especially with screed laid over insulation or under floor heating. Dave Taylor explains: “Main contractors and developers are under so much pressure to get jobs finished and want to work on the floor as quickly as possible.” “What we try and do is to advise them on the choice of products that offer various drying times and options to improve the programme.” Spencer Warner of contractors CSC Screeding agrees: “Perhaps the biggest problem in the market place for screeders is plant being driven over screeded floors before they have cured properly. “You often see scissor lifts running over floors before they have reached their final strength 28 days after installation. If they’ve not set properly they won’t take the loads of modern plant and the floor gets damaged. “Concrete technology has changed considerably during recent years and by using additives the speed of hardening and setting can be controlled. What once took a month can now be achieved in hours. “Being able to offer a main contractor a shorter installation period and hand the area over early is a big bonus.” The load capacity of any screed laid on insulation is dictated by the strength of
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that insulation. Screeds and insulation react in different ways. All screeds, no matter how well laid or strong, are at risk of cracking. British Standards recognise that screeds tend to crack randomly as they dry and shrink. Dave Taylor says this can occur because areas are not sealed properly to allow curing: “Rooms need to be a sealed environment and then opened up to allow the floor to breath.” Peter Dolby, commercial director at Isocrete, adds: “The risk of cracking is highest for floating and unbonded screeds; they are usually reinforced to help control crack width and spacing.” Fast-drying screed such as Ardex, FlexiDry, Isocrete’s K-screed, and Tarmac’s Truscreed, use super-plasticisers to reduce the amount of water needed to make the screed mixture pliable; this in turn makes for a fast drying time as there is a higher cement to water ratio. The drying times for these are generally around 3mm per day. FlexiDry is the most recent entrant of these into the market. Simon Bateman,
the company’s technical manager, says: “FlexiDry fast drying floor screed is 20 to 30 per cent more efficient as a thermal conductor than an anhydrite screed. “A standard screed laid at 75mm depth will generally take at least 110 days to dry before you can lay your final floor finishes. With our new F0 fast drying floor screed you can lay your flooring finishes after just three days.” Floors have joined mechanical and electrical services as another excuse for the delay on a whole range of projects. But more often than not it’s the pressure of time and perhaps a lack of understanding that sees other trades being asked to work on screeded floors before they are ready and so damaging them. When specifying a flooring screed, it is important that clients take all the relevant factors into account during the decision-making process. It’s important that they assess what ‘fast-track’ means and the effect it will have on a programme but what’s clear is that the potential implications of using new screed technology on programme is considerable.
FLOORING AND SCREEDING Flexidry F2 fast drying screed is being installed at Uxbridge College in Middlesex
Fast drying in Uxbridge, Middlesex FlexiDry’s F2 (14-day dry time) fast drying floor screed is being installed on an underfloor heating system at Uxbridge College’s new £6 million sports and leisure development which will include indoor and outdoor facilities for a wide range of sports and activities. Kier Group is main contractor for the new sports hall and chose FlexiDry for its ability to change the screed dry time on site with just one product, but also thanks to its sustainable qualities including reduced thickness, less waste and increased thermal conductivity. Originally a 21-day dry time option was chosen for the project but as timescales came under pressure to have the final floor finishes laid, Kier changed to use the 14-day dry time option. This was able to be done without any change to the specification. The new sports hall caters for a wide range of activities including five-a-side football, cricket, basketball, netball and volleyball, and there’s a full-size electronic scoreboard. The hall will be 50 per cent taller and 50 per cent bigger than the original building. The new hall will also be used for Uxbridge College’s Sports Academies in football, basketball and cricket, enabling the college to expand its range of sport coaching qualifications.
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September's issue of the FPDC Specialist Building Finishes Magazine has an article on fast drying floor screeds and also includes a case st...