What is it?
Stopgap P121 is an acrylic primer designed to promote the application characteristics of calcium sulphate-based levelling compounds, such as F. Ball’s Stopgap 1100 Gypsum, when applied over calcium sulphate screeds.
Priming with Stopgap P121 also helps to prevent the unacceptably rapid drying of subsequently applied levelling compounds, which may lead to floor failure. It also helps to avoid ‘pinholing’ – small holes in the levelling compound that are caused by the slow escape of air from absorbent surfaces and have the appearance of pinholes or blisters once fully cured.
Where is it used?
Over calcium sulphate screeds (e.g. anhydrite) before the application of a calcium sulphate-based levelling compound. It is also suitable for use over normal underfloor heating installations.
F. Ball recommends a calcium sulphate-based levelling compound over calcium sulphate screeds to ensure maximum compatibility, limiting the stress at the bond interface and minimising the chances of floor failure. It also avoids the formation of ettringite, a crystalline material caused by a reaction between cement-based levelling compounds and calcium sulphate screeds in damp environments, which can lead to floor failure.
How to apply:
Use a paint roller or medium stiff brush. Begin by making sure the screed is suitably sound, smooth and dry. It should be free of laitance and subfloor relative humidity (RH) levels should be below 75% (65% where wood floorcoverings will be applied). Apply in two coats. The first should be diluted with one part primer to one part water. Once dry, apply a second, neat coat of the primer.
Why it works:
The primer contains finer particles than others in the F. Ball range, helping it to bond with calcium sulphate screeds, which are denser and more solid than concrete or sand/cement screeds, in order to promote adhesion and application properties of subsequently applied levelling compounds.
What else is different about it?
Stopgap P121 is coloured blue to provide the user with visual control of coverage uniformity, and like other F. Ball primers and liquids, it now comes in recycled 5 litre plastic bottles, which are also made from recyclable materials.