STOPGAP 850 is a non structural exterior grade smoothing compound for use in light to medium duty applications to smooth and level rough or mechanically damaged concrete or sand / cement screeds.

STOPGAP 850 is ideally suited for smoothing areas such as balconies, patios, garage sand walkways and is unaffected by rain or frost when set and dried. It is also suitable for smoothing subfloors prior to the application of a suitable non-slip coating or external covering such as artificial grass.

STOPGAP 850 is also suitable for internal application over damp, uneven concrete and sand/cement screeds, prior to application of STOPGAP Waterproof Surface Membranes and STOPGAP ISOLATOR MEMBRANE.

STOPGAP 850 can be left as a stand-alone exterior wearing surface. To give a more natural surface finish and to reduce the potential for slip, if left uncovered, it is recommended that a scratch coat is applied to the surface and brush finished to a textured profile.

STOPGAP 850 can also be pump applied up to 900m2 per day, dependent upon manpower, thickness applied and equipment used.

Absorbent surfaces – Concrete and sand/cement screeds must be primed with STOPGAP P131 diluted 1:7 with water

General information

Uniclass 2015

Pr_35_31_06_80 Smoothing and levelling underlay compoundsPrimary


M10/157 Proprietary surfacing to lightweight aggregate levelling screeds M10/

Specification data - Smoothing and levelling underlay compounds

Product Reference

Stopgap 850 Exterior

Product Options

Technical properties:

  • Class (to EN 1504-3:2005): Class R2
  • Working time at 20°C: 10–15 minutes.
  • Setting time at 20°C: 2 hours.
  • Consumption per mm thickness: 1.72kg/m².

Compressive strength (N/mm², to EN12190):

  • 28 Days: >25.0

Flexural strength (N/mm², to EN196-1):

  • 28 Days: >6.0


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