Nullifire FS703 Intusil Fire Resistant Silicone Sealant


Nullifire (Firetherm) FS703 Intusil Fire Resistant Silicone Sealant, a fire-stopping sealant designed for aggressive exterior use on high-sheen surfaces (glass, aluminium) and in high-movement joints for up to 50% movement. Suitable to fire seal joints in
compartment walls and floors such as masonry to masonry, masonry to timber, masonry to steel - see the description below for a list of suitable surfaces and substrates.

  • Up to 4 hours fire resistance - Tested to EN 1366-4
  • Tested in gaps 10 - 220 mm
  • Ideal for joints in flexible walls, rigid walls & floors, windows & door frames
  • Airtight up to 600 Pa
  • Superior elasticity
  • Excellent tooling properties
  • UV & weather resistance
  • 20% Movement tested
  • Black and grey colours available on request

To qualify for Express (1-3 day) shipping, basket value must exceed £75.00 + VAT. Orders below this amount will only be available on Economy (7-10 day) shipping

£105.12(ex. VAT)
£126.14 (inc. VAT)
Please choose your colour
Available for Delivery (See Delivery Options Below)


Nullifire FS703 Intusil Fire Resistant Silicone Sealant  provides a fire-stopping seal around high movement joints and is ideal for use in external aggressive environments, with high adhesion that applies to high-sheen surfaces like glass and aluminium. The mastic insulates and resists fire for up to 240 minutes with a water-resistant seal that is unaffected by moisture, offering a movement capability of up to 50%.

Intusil cures at a rate of 1 mm per day and cannot be readily over-coated.

Sealing gaps and cracks in fire barriers and around services can be critical to slowing the spread of smoke and fire, saving lives with more time for evacuation. Use FS703 Intusil in the following applications:

  • Block to block
  • Block to steel
  • Concrete to timber
  • Block to concrete
  • Plasterboard heads
  • Floor movement seals
  • Head of wall movement seals
  • Slab edge seals
  • Service movement seals
  • Static linear joints (masonry to masonry/rigid wall/rigid floor/flexible wall)
  • Window & door joints (masonry to timber/steel)
  • Movement joints (20%)


  • 2:1 ratio wall 240 minutes integrity; 240 minutes insulation
  • 2:1 ratio floor 240 minutes integrity; 90 minutes insulation
  • 3 mm over 100 mm Firetherm Backer 240 minutes integrity; 240 minutes insulation; 30% movement
  • 10mm angled fillet to Intubatt edges or full depth plus fillet around services

Maximum Openings

  • Linear gaps up to 50 mm x infinite length


  • 10 mm wide seal - 3.25 m approx.
  • 15 mm wide seal - 1.35 m approx.
  • 20 mm wide seal - 0.78 m approx

Fire Testing

  • Tested at Exova BM Trada to BS EN 1366-4, BS EN 1366-3, BS 476/20/22
  • Third party accredited by Exova Warrington Fire, certificate number CF 5340

IMPORTANT FIRE PRODUCTS NOTICE:  The information displayed on this website should be used as a guide ONLY and  our Technical Department should be contacted to obtain a tailored specification and any advice necessary before you place an order for fire protection products. Fire protection products are non-returnable except in accordance with  Condition 8 of the Terms and Conditions .  We will not be held liable for any resulting damage to property, human life or monetary costs incurred due to the incorrect specification you have prepared or use of fire protection products caused by your negligence, including your failure to have contacted us to obtain the relevant advice/specification.

Product Details

Customer agrees that before placing an Order, Customer has read and understood the most up to date Product Data Sheet for the Product. Where we have access to the Product Data Sheet from the manufacturer, we will either provide a copy on request, or include a link to the Product Data Sheet available on the manufacturer’s website. Customer further agrees that we have no liability for any errors or omissions contained within the Product Data Sheets. For more information, please see our Terms & Conditions of Sale.

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