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Firestem Intumescent Mastic

Insulation Products: Fire Protection Products > Fire Stopping Products

Product Code: 39588

FS Intumescent Mastic

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Product Description:

High performance acrylic based construction sealant for sealing joints and cracks in fire rated internal walls and floors. In the event of fire Firestem™ Intumescent Mastic provides a barrier to flame and smoke preventing the spread of the fire and toxic gases through building joints. 4 hour fire rating on brick, concrete, steel and vermiculite with a single 12.5mm deep seal.

Water based and easy to apply. Firestem™ Intumescent Mastic forms a flexible seal with good adhesion to most common building materials.

When subjected to heat Firestem™ Intumescent Mastic swells (intumesces) to provide an inert barrier to smoke and flame. The fire resistance achievable with Firestem™ Intumescent Mastic depends upon the joint design, depth of sealant and substrates being sealed.


Firestem™ Intumescent Mastic is tested by Warrington Fire Research Consultants to BS476 part 20 and achieves 4 hours Fire Resistance


  • All surfaces to be sealed must be clean, dry and free from grease, latience or dust
  • Apply mastic over a polyethylene backing rod to a minimum depth of 12.5mm
  • Whenn applying, ensure all crevices are filled and there is complete contact between sealant and substrate.  Tool down using a wetted spatula.  Any excess may be removed using soapy water before mastic dries.
  • note: Depth of seal must not exceed width
  • The fomula for calculating the linear metres per cartridge is as follows: 
    310 ÷ gap width (mm) x gap depth (mm)

Click on the Sub Code for more details.

Sub Code
310ml Cartridge

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