Fire rated vs intumescent sealant: which do you need?
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Fire rated sealant and intumescent sealant both hold back fire and smoke, but they work differently. An intumescent sealant swells when it gets hot (above about 125°C) to seal the gap and block fire and smoke, it is the one for pipe and cable penetrations and joints in fire-rated walls and floors. "Fire rated sealant" is the broader term and also covers fire-rated silicones for movement joints. For sealing gaps and service penetrations in a fire wall, use an intumescent sealant like Everbuild Firemate, rated up to 4 hours in the right joint. Match the sealant to the joint and the fire rating the job needs.
What is a fire rated sealant?
A fire rated sealant is any sealant tested and certified to resist the passage of fire and smoke through a joint for a set time. It is an umbrella term: it covers intumescent acrylic sealants and fire-rated silicones, which do the same broad job in different joints. The rating (30, 60, 120 or 240 minutes) is what the tested joint holds fire back for, not a property of the tube alone.
What is an intumescent sealant, and how does it work?
Intumescent means it expands when heated. Our Everbuild Firemate is an acrylic intumescent sealant that swells to more than 150% of its size once it passes about 125°C, closing the gap tight and stopping fire and smoke getting through. It is fire rated to EN1366-4, up to 4 hours in certain joint configurations, and it is acoustic rated too, so it seals sound as well as fire. It needs no primer on most construction substrates.
Intumescent or fire-rated silicone: which do you need?
It comes down to whether the joint moves:
| Intumescent acrylic | Fire-rated silicone | |
|---|---|---|
| How it seals fire | Swells with heat | Holds and resists heat |
| Movement | Low-movement, static gaps | Higher-movement joints |
| Best for | Pipe and cable penetrations, linear gaps | Perimeter and movement joints |
| Water/wet areas | Interior, dry | Better in damp conditions |
| Overpainting | Usually yes | No |
For the common job, sealing around pipes and cables where they pass through a fire wall or floor, and filling linear gaps, an intumescent acrylic is the one. Use a fire-rated silicone where the joint has to flex, such as a movement or perimeter joint.
What do the fire ratings mean?
Fire ratings are given in minutes, typically 30, 60, 120 or 240 minutes. That is how long the tested joint holds back fire in a fire test. The important bit trades miss: the rating belongs to the whole tested detail, the sealant, the joint width and depth, the backing and the substrate, not to the sealant on its own. A product rated "up to 4 hours" only achieves that in the specific joint it was tested in. Match the tested detail to the fire rating the building needs.
Where do you use fire sealant?
- Service penetrations: around pipes, cables, ducts and conduit where they pass through a fire-rated wall or floor.
- Linear gaps and joints in fire-rated walls and floors.
- Head-of-wall and perimeter joints where a partition meets the structure.
- Around fire door frames and other fire-stopping details.
How to apply it
- Get the joint clean and sound, and use a backing (fire-rated backer rod or board) for deep joints so the sealant is the right depth.
- Fill to the tested depth and width, tooling the sealant into the joint. Too thin a bead will not make the rating.
- Follow the tested detail for the rating you need, this is fire-stopping, so the certified configuration matters.
- Load the tube in a sealant gun and run a full, continuous bead.
Common mistakes to avoid
- Ordinary sealant in a fire joint. Only a certified fire or intumescent sealant holds a rating. Decorators caulk and standard silicone do not.
- Assuming any gap gets the headline rating. The rating is for the tested detail. Match the joint to it.
- Bead too shallow. Fill to the tested depth with the right backing, not a thin smear.
- Wrong type for a moving joint. A static intumescent in a movement joint cracks; use fire-rated silicone there.
The short version
Intumescent sealant swells with heat to seal gaps and service penetrations in fire walls and floors; fire-rated silicone handles the joints that move. Both carry a fire rating in minutes, but that rating belongs to the tested joint, not the tube. For pipes, cables and linear gaps, reach for an intumescent acrylic like Everbuild Firemate. Browse the full sealants and silicones range.
By Steve, Builders Hardware Direct. Steve runs the BHD trade counter and has spent years supplying sealants, fire-stopping and site consumables to builders and fit-out trades across South Wales. Not sure which sealant? Call the counter on 01269 267030 or order online for fast UK delivery.
