Product Description

FireMastic-300™ (Fire and Acoustic Rated Sealant)

Flexible fire and acoustic rated acrylic intumescent sealant. Suitable for sealing joints, linear gaps and service penetrations. Our 5 hour fire rated sealant offers the best fire rating of all acrylic and PU sealants on the market, offering maximum protection from fire and smoke in both integrity and insulation. With an FRL of up to -/300/300, FireMastic-300™ is unrivalled.

As an acrylic emulsion, FireMastic-300™ is simple to use and cleans up easily in water.

Key features include:

  • 5 hours industry leading mastic offering up to FRL of -/300/300
  • Acoustic reduction up to 67dB
  • Used for sealing linear gaps and around service penetrations such as ducts, dampers, cables and metallic pipes
  • For use inconjunction with many other BOSS firestopping products.
  • Certified for use in concrete, plasterboard, masonry, AAC, Hebel, Speedpanel, Korok, AFS, Shaftliner, Dincel and timber installations
  • Approved to AS1530.4(2014), AS4072.1 and BS EN1366
  • Highly flexible, up to 40% movement
  • High yield so installation material costs and labour are both decreased
  • Gap widths up to 50mm
  • Available in standard colours of grey and white, other colours available upon request
  • Widely adaptable to seal around other passive fire products such as dampers, pillows, collars and batts
  • Can be painted once cured


  1. Ensure that the gap, aperture and/or services in question are tested with BOSS FireMastic-300™ and the site conditions are within the application specification.
  2. Ensure all surfaces are clean, dry and free from grease.
  3. Use masking tape to provide straight edges around surfaces, if required for aesthetics.
  4. Please refer over page under backing rod to determine of a backing rod is required.
  5. Cut nozzle to required bead size and apply to substrate via a caulking gun. Smooth out sealant with a wet spatula within 5 minutes for professional finish.
  6. Clean tools immediately after use with water.
  7. Tack dry within 30mins, cures 3mm per 24hrs.­

Call our Tech Services team on 1300 50 BOSS to find out more about how FireMastic-300™ can assist your project needs.


Technical Datasheet     Safety Data Sheet     VOC

Product Details

Part ID : FM300

Size :

  • 300mL cartridge
  • 600mL sausage

Colour : Grey and White