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Single part fire rated acrylic sealant designed for internal perimeter pointing of fire rated door and window frames where the integrity of fire walls or partitions needs to be maintained. The sealant is formulated to intumesce on exposure to high temperatures to form a fire and smoke resistant 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 unprimed adhesion to most construction substrates and can be overpainted.

Features/ Benefits:

  • Swells at high temperature to give a fire and smoke resistant seal.
  • Four hour fire rating.
  • Environmentally friendly.
  • Paintable.


  • Door and window perimeter pointing.
  • Partition joints.
  • Perimeter pointing to fire wall penetrations.
  • Low movement block work joints.

Standard product features

Technical properties:

  • Solids content: 100%.
  • Application temperature: 5–40°C.
  • Service temperature: -40 to +120°C when cured.
  • Skin time: 30–45 minutes (at 23°C and 50% relative humidity).
  • Cure time: 2 mm/24 hours (at 23°C and 50% relative humidity).
  • Specific gravity: 1.6.
  • Hardness: 20–25 Shore A.
  • Movement accommodation: 20%.
  • Minimum joint width: 6 mm.

NBS Specification

NBS Create logo
This product is associated with the following NBS Create clause:
45-55-75/320 Acrylic construction joint sealants

Product specification

An important note about specifying





+44 (0)114 2409409

Product reference

Firex® 321



Manufacturer details

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