ON THE LEVEL
F. Ball and Co. Ltd offers expert advice on working with calcium sulphate screeds.
The speed with which they can be applied over large areas and quicker drying times has meant that calcium sulphate screeds (or anhydrite screeds) have become a popular choice of subfloor in new-builds. When installing new floorcoverings over screeds, it is essential to take the time to assess the condition of the subfloor and suitably prepare it, before choosing a compatible levelling compound.
THE PREPARATION PROCESS As with any screed, a moisture measurement test should be conducted to determine whether a calcium sulphate screed subfloor is dry enough to proceed directly to installing floorcoverings. If the relative humidity of the subfloor is above 75%, contractors will need to allow further time for the screed to dry. It is also essential to remove any laitance, a crust of cement and fine aggregates formed on the surface of the screed as it dries, as failing to do so will increase the subsequently applied levelling compound’s risk of failing.
After ensuring the subfloor is suitably smooth and dry and free of contamination, the contractor can then proceed to prime the subfloor. Priming helps to promote the adhesion of the levelling compound to the screed and prevents unacceptably fast drying, which can weaken the levelling compound and lead to floor failure. F. Ball’s Stopgap P121 primer is specially formulated to promote the application characteristics of compatible levelling compounds when applied over calcium sulphate screeds.
CHOOSING THE RIGHT
LEVELLING COMPOUND Calcium sulphate-based levelling compounds, rather than cement-based ones, offer maximum compatibility with calcium sulphate screeds. This is because the use of cement- based levelling compounds over calcium sulphate screeds can produce a chemical reaction resulting in the formation of ettingite crystals, and this can ultimately cause a floor failure.
Stopgap 1100 Gypsum is F. Ball’s calcium sulphate-based levelling compound designed especially for application over calcium sulphate screeds. It can be applied at thicknesses between 2–10mm, has excellent self-levelling properties and can be pump-applied up to 1500m2
“Cement-based levelling compounds over calcium
sulphate screeds can produce a chemical reaction and cause a floor failure.”
Club, in Middlesex. Contractors from Middlesex Flooring used a rotary sanding machine to remove laitance from the newly- installed anhydrite screed subfloor to prepare the surface ahead of the application of a levelling compound. A moisture test was also carried out, and it was determined that the subfloor was dry enough to receive floorcoverings.
per day, dependent
upon manpower, thickness applied and equipment used. It is also low-odour and protein free, making it suitable for use in biologically sensitive areas, such as hospitals.
CASE STUDY F. Ball products including Stopgap 1100 Gypsum were used to install high-quality floorcoverings in an upstairs function room in the newly-built clubhouse at CB Hounslow United Football
22 | SCREEDS & RESINS
Stopgap 1100 Gypsum was then applied to create a perfectly smooth surface ahead of the installation of the floorcoverings. Stopgap 1100 is self-levelling, so when mixed, the compound was poured onto the prepared substrate and allowed to flow and achieve a thickness of 3mm. The compound was ready to receive floorcoverings 24 hours later.
Craig Gargan, of Middlesex Floors, said: “We received great support from F. Ball throughout the job, including with the site survey and moisture testing. As usual, using their products meant that it was straightforward and there were no problems.”
www.f-ball.co.uk www.tomorrowscontractfloors.com
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