Fire rated sealant is a sealant tested to stop fire and smoke passing through a joint or small opening for a set time. Intumescent types swell in heat to close gaps around pipes and cables. Acrylic and silicone types seal joints that move. Each is rated only for the gap size, depth, backing and substrate it was tested with.
What is fire rated sealant?
Fire rated sealant, also called fire sealant or fire retardant sealant, is a sealant that has been tested to resist the passage of fire, smoke and heat through a joint or small opening for a stated time. It is one part of passive fire protection, used wherever a compartment wall or floor has a gap that must be closed but still allow some movement.
The important word is tested. A fire rated sealant is not rated on its own. It is rated as part of a tested arrangement: the product, the width of the gap, the depth of sealant, the material behind it, and the wall or floor it sits in. Change one of those, and the test result no longer describes what is on site. We explain this idea in more detail in service penetrations and fire stopping.
The main types of fire sealant
| Type | How it works | Typical use | Watch for |
|---|---|---|---|
| Intumescent acrylic | Swells in heat to close gaps | Around plastic pipes, cables and small penetrations | Gap and pipe sizes must match the test |
| Fire rated acrylic (non-intumescent) | Holds its place and resists heat | Linear joints in walls and between wall and slab with modest movement | Limited movement capacity |
| Fire rated silicone | Flexible, keeps sealing as the joint moves | Joints with larger movement, some facade and expansion joints | Usually costs more; check it is the fire-tested grade |
| Graphite based sealant | Expands strongly in heat | Some pipe and cable penetrations | Use only where tested |
Many buildings need more than one type. A floor might use intumescent sealant around small pipes, acrylic along the top of block walls, and silicone in a movement joint at a column. Using one product everywhere because it is convenient is one of the most common faults we find.
Joints versus penetrations
Fire sealants do two different jobs, and products are often tested for one and not the other.
Linear joints are long, narrow gaps: where a wall meets the slab above, where a partition meets a column, or an expansion joint across a floor. These move as the building moves. The sealant must stay bonded and keep sealing through that movement, and still resist fire. Test methods for joints include EN 1366-4 and UL 2079.
Penetrations are openings around something passing through: a pipe, a cable or a bundle of cables. The service itself can melt, burn or conduct heat. The sealant must close the gap as that happens. Test methods for penetrations include EN 1366-3 and ASTM E814 or UL 1479. A product tested only as a joint seal has no evidence for use around a plastic pipe, and the reverse is also true.
Why depth and backing decide the rating
In most tested systems the sealant is not used alone. A packing of mineral wool goes into the gap first, compressed to fill it, and the sealant is applied over it to the depth shown in the test. The mineral wool carries much of the fire resistance. The sealant closes the surface against smoke and holds everything in place.
On many sites we find the sealant applied as a thin bead over an empty gap, or over a foam backing rod meant for ordinary weatherproof joints. Foam rod burns. A thin bead over nothing burns through in minutes. From the room side, both look identical to a correct joint. The difference only shows in a fire, or when someone probes the joint and finds it soft.
Where sealant is the wrong answer
Sealant suits joints and small openings. It is the wrong choice for large openings such as cable shafts through slabs, where it cannot span the gap. Those need fire stop mortar over a reinforced backing, as we describe in shaft closing. It is also a poor choice for cable trays that are changed often, where every new cable means cutting the seal. Fire pillows suit those better.
How to check fire sealant on site
- Ask for the product data and the test report, and check it covers this type of joint or penetration.
- Check the gap width against the range in the test.
- Probe the joint with a blunt tool. Firm resistance usually means mineral wool behind it. Soft give usually means foam rod or nothing.
- Look for ordinary builders' foam or silicone near rated walls. If it is there, it is not fire stopping.
- Check that the work is photographed and logged, so it can be traced later.
For a full record of what each joint should be, see why installation documentation matters. Most of these checks are easy to do before the ceiling closes and very hard after.
ASTM E814, fire tests of penetration firestop systems. EN 1366-3:2021+A1:2024, penetration seals. UL 2079, fire resistance of building joint systems. National Building Code of India, Part 4 (Bureau of Indian Standards). Test standards and rules are revised, so check the current edition for your project. Last reviewed 27 October 2026 by the Simfy Firesys team.
Where we fit, and where we do not
We install fire retardant sealants and joint seals using CBRI tested products, applied to the depth and backing the system asks for, with each joint photographed. We do not supply weatherproof facade sealants or general construction sealants. If you are not sure what is in your joints, or need them checked before an inspection, talk to our team.
