STOPGAP P121 is an acrylic primer designed to promote the application characteristic sof STOPGAP 1100 GYPSUM, and other suitable STOPGAP smoothing under layments, to calcium sulphate screeds e.g. anhydrite. It prevents unacceptably rapid drying of adhesives and smoothing under layments. It is non-flammable and suitable for use over normal underfloor heating installations. STOPGAP P121 is coloured blue to provide the user with visual control of coverage uniformity

Floor surfaces must be suitably prepared; sound, smooth, dry (<75%RH) and free from contaminants that may prevent adhesion. Calcium sulphate screeds e.g. an hydrite should be prepared in accordance with manufacturers instructions and thoroughly vacuumed to remove any remaining dust prior to the application of STOPGAP P121.The temperature of the surface must be above 5°C when the primer is applied to the subfloor and underfloor heating must be off for at least 48 hours before, during and after application. Ensure the subfloor is dry and incorporates an effective damp proof membrane.

General information

Uniclass 2015

Pr_35_31_66_94 Water-based acrylic primersPrimary


M10/160 Proprietary self smoothing levelling screeds

M10/7 Proprietary quick drying levelling screeds

M42/10 Wood flooring

Specification data - Water-based acrylic primers

Product Reference

Stopgap P121

Product Options


For dry (<75%RH) and suitably prepared calcium sulphate screeds, prime with two coats of STOPGAP P121. The first coat should be diluted 1 part primer to 1 part water. Once dry, prime with a second coat of neat P121.

Apply evenly to the whole surface to be treated and allow it to dry completely