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Single part fire rated MS Polymer based sealant designed for sealing expansion joints and compression joints where frequent movement is anticipated as part of a fire resistant assembly. The sealant is formulated to intumesce on exposure to high temperatures to form a fire and smoke resistant joint seal.

It is non-hazardous, will not emit halogenated by products under fire conditions and contains no raw materials known to have an oestrogenic effect in the environment. The sealant offers excellent levels of adhesion to most construction substrates and can be overpainted with oil, polyurethane or latex paints.

Features/ Benefits:

  • Swells at high temperature (250°C) to give a fire and smoke resistant seal.
  • Four hour fire rating.
  • Environmentally friendly.
  • Paintable.
  • High movement accommodation.
  • Resistant to UV Light.
  • Elastomeric intumescent seal.
  • Abrasion resistant including foot traffic.


  • Public buildings.
  • Sports stadia.
  • Hospitals.
  • Schools.
  • Hotels.
  • Factories and offices.
  • Railway and airport terminals.
  • Off shore structures.
  • Oil terminal Bund walls.
  • Oil terminal floor slabs.

Related literature

The following content references this product:

Standard product features

Technical properties:

  • Solids content: 100%.
  • Application temperature: 5–40°C.
  • Service temperature: -40 to +150°C.
  • Skin time: 30–35 minutes (at 23°C and 50% relative humidity).
  • Cure time: 3 mm/24 hours (at 23°C and 50% relative humidity).
  • Hardness: 35 Shore A (approximate).
  • Movement accommodation: 50%.
  • Minimum joint width: 6 mm.

NBS Specification

NBS Create logo
This product is associated with the following NBS Create clause:
45-55-75/315 Construction joint sealants

Product specification

An important note about specifying





+44 (0)114 2409409

Product reference

Firex® 921 MS



Manufacturer details

Thorncliffe Park,
Sheffield, S35 2YP
Tel +44 (0)114 2409409
NBS Plus