STOPGAP 1100 GYPSUM is a self-levelling smoothing underlayment designed specifically for application over sound calcium sulfate (e.g. anhydrite) screeds prior to the installation of new floorcoverings.

Dimensionally stable and is supplied as a pre-blended dry powder, which is designed for application between 2–10 mm. It is protein-free which allows it to be used in biologically sensitive areas such as hospitals.

Calcium sulfate-based and is particularly compatible for smoothing and levelling similarly constructed screeds but may also be used over a wide range of other subfloor types including STOPGAP waterproof surface membranes, sand/ cement screeds, concrete, sound asphalt, granolithic, terrazzo, epoxy and polyurethane resins, ceramic and quarry tiles.

Can be pump applied up to 1500 m² per day, dependent upon manpower, thickness applied and equipment used.



  • Absorbent surfaces - For dry (<75% RH) and suitably prepared calcium sulfate screeds, prime with two coats of STOPGAP P121. The first coat should be diluted one part primer to one part water. Once dry, prime with a second coat of neat P121. For all other absorbent surfaces prime with dilute STOPGAP P131 to prevent rapid drying of the underlayment.
  • Non-absorbent surfaces – such as sound flooring grade asphalt, minimal adhesive residues, terrazzo, quarry tiles and STOPGAP waterproof surface membranes should be primed with neat STOPGAP P131 to ensure that good adhesion is obtained between the underlayment and substrate.
  • Primers should be used in accordance with instructions printed on the bottle and must be allowed to dry before applying the smoothing underlayment.

General information

Uniclass 2015

Pr_35_31_06_80 Smoothing and levelling underlay compoundsPrimary


M13/120 Proprietary self smoothing levelling screeds

Specification data - Smoothing and levelling underlay compounds

Product Reference

Stopgap 1100 Gypsum

Product Options

Technical properties:

  • Class (to BS EN 13813): CA-C30-F7.
  • Working time at 20°C: 20–30 minutes.
  • Setting time at 20°C: 2 hours.
  • At 3 mm ready to receive textile floorcoverings: 24 hours.
  • pH (to BS EN 13454): 10–12.
  • Consumption per mm thickness: 1.60 kg/m².

Compressive strength (N/mm², to BS EN13892-2):

  • One day: >10.0.
  • Seven days: >15.0.
  • 28 days: >30.0.

Flexural strength (N/mm², to BS EN13892-2):

  • One day: >2.0.
  • Seven days: >3.0.
  • 28 days: >7.0.


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