ON THE BALL:
WORKING WITH CALCIUM SULPHATE SCREEDS
In this issue’s Tip of the Month,Stephen Boulton, Technical Service Manager for F. Ball and Co. Ltd., provides guidance on installing floorcoverings over calcium sulphate screeds.
Calcium sulphate screeds have become a popular choice of subfloor to install in new builds. This is because of the speed with which they can be applied over large areas, quicker drying times compared with concrete and the ability to force-dry them in as little as seven days. However, when installing new floorcoverings over calcium sulphate screeds, it is essential to take the time to assess the condition of the subfloor and suitably prepare it, and then to choose a compatible smoothing underlayment.
The first thing to do when working with calcium sulphate screeds is to ensure that the subfloor is suitably sound, smooth and dry. Any laitance should be removed; this is normally done using rotary sanding or abrading machines. Any contaminants that may prevent adhesion, such as wet trade waste or debris, should also be cleaned off.
Just as when installing floorcoverings over any other subfloor type, a moisture measurement test should be conducted to ascertain whether the subfloor is dry enough to proceed directly to installing floorcoverings.
If the relative humidity of the subfloor is below 75%, the contractor can proceed to the next stage of the flooring installation: priming. Priming a calcium sulphate screed is essential to the overall appearance and performance of
22 | TIP OF THE MONTH
the floor. It helps to promote the adhesion of the smoothing underlayment to the screed and prevents the unacceptable drying of the underlayment, which can result in floor failure.
Another reason that contractors should ensure that the relative humidity of the substrate is sufficiently low, is that the application of a cement-based levelling compound onto a calcium sulphate screed in a damp environment can result in a reaction taking place that leads to the production of ettringite. Ettringite is a crystalline material which can cause floor failure. Therefore, F. Ball recommends a calcium sulphate-based self-levelling compound; to avoid any potential of this reaction occurring.
One such levelling compound to offer maximum compatibility with calcium sulphate screeds is F. Ball’s Stopgap 1100 GYPSUM. Unlike most cement-based products, Stopgap 1100 levelling compound is virtually tension free and does not shrink during the drying process, which limits the amount of stress at the bond interface. As well as providing a specialist solution for the levelling of suitably prepared calcium sulphate screeds, the compound can be effectively used over a wide range of surfaces including waterproof surface membranes, concrete and sand:cement screeds.
www.f-ball.com/en www.tomorrowscontractfloors.com
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