Ross Verity, Managing Director of Force-Dry outlines how force drying liquid screeds can save time and money.
SCREED TO GO FASTER!
The development of flowing gypsum screeds in recent years has brought many advantages to flooring installation. For example, liquid gypsum screeds are superior in many ways to sand/cement; they are quick and economical to install, do not curl, need no reinforcement and large bays can be laid without risk of cracking. They have excellent conductive properties so are highly efficient and economical when used with underfloor heating.
Crucially, liquid gypsum screeds are also more environmentally friendly than sand/cement screeds; comprising 98% recycled waste material they require less energy to produce and, because they are thinner, they use less material. These factors result in a carbon footprint over 70% lower than that of sand/cement screeds. As a result, a 50mm gypsum screed contains 20Kg less embedded carbon per square metre than a 75mm sand/cement equivalent.
But in my view, one of the most notable advantages of flowing gypsum screeds is that they can be force dried quickly and safely provided the right equipment is used and best practice is observed.
Time is money in construction, so being able to reduce installation time for liquid screed floors in this way represents a very significant cost saving for contractors and developers alike, and brings welcome certainty to any construction programme.
The drying times given on screed datasheets are generally based on a fixed environment, at 20˚C and 60% relative humidity throughout the stated drying period. But it is rarely, if ever, possible to achieve these conditions naturally on a construction site in the U.K. Typically an anhydrite screed, installed at 50mm depth, will be said to have a drying time of 60 days, but on a construction site this will often extend to 90 days or more. However, using the force dry method can bring the drying/commissioning time down to as little as 28 days for a 50mm screed.
The key to successful force drying is control, both of the environment and the technical process.
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Even in the hottest weather, variations in temperature and drafts will impact on the drying process - and it is a misconception that force drying isn’t necessary in heatwaves.
Doors, windows and other spaces that are not enclosed will delay the drying process, as will water ingress, spillages and using water to damp down. Removal of laitance, good ventilation and use of dehumidifiers are key and HEPA type filters can also be helpful. Testing screeds for moisture has become a critical process requirement particularly where installing over sensitive flooring or impermeable membranes. However, while several standard moisture test methods are available, no single test reveals everything that should be considered when deciding if flooring can be installed or a coating applied. We recommend a combination of non- invasive and invasive methods: non-invasive thermal imaging cameras can be used to identify potential moisture spots; the invasive approach is a more robust, accurate method which involves drilling a ¾ inch hole to suitable depth of screed and inserting an adjustable humidity sleeves with hygrostick sensor. Once the sleeve has acclimatised (normally 2-3 hours), a reading can be taken and recorded using the instrument’s data logger.
It is also essential to accurately control temperature and distribute heat evenly during the heating and cooling programme. Specific boiler technology designed solely for the purpose should be used and it’s vital there are sufficient boilers of the correct size for the job.
Using this custom-made system reduces the risk of floor failure and associated expensive remedial costs.
Programme timings are critical to the success of any construction project. With site running costs and penalty clauses for over runs taken into consideration, the time, cost and certainty benefits this force drying method brings to a project are clear.
www.force-dry.co.uk SCREEDS, RESINS & COATINGS | 27
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