What is fire-rated sealant, and where do I have to use it?
The difference between intumescent, fire-resistant and acoustic products, why fire-stopping is a tested system rather than a tube, and where the boundary of DIY sits.
- Difficulty
- advanced
- Time
- 20 min
- Read
- 4 min
- Safety
- restricted
Short answer
Fire-rated sealants are tested as part of a complete system — a specific product, at a specific depth, with a specific backing, in a specific construction — and they only perform if used exactly that way. Intumescent products swell in heat to close a gap; fire-resistant ones simply do not burn through. Anything sealing a hole through a fire-resisting wall or floor is regulated work, and in flats it is specialist work.
This subject sits at the boundary of what a householder should do, and the honest answer is that most of it is over the line. Fire-stopping failed at scale in British buildings because the details were treated as sealing rather than as engineering, and the regulatory response has been to tighten the requirement for tested systems and documented installation. It is worth understanding what the products do, so that you know when you have crossed into work that needs someone else.
Safety
Step by step
- Understand what a fire-resisting element is.A wall, floor or ceiling designed to hold fire back for a stated period — commonly the wall between a flat and a common corridor, the floor between flats, a garage-to-house wall, and the structure around a protected stairway. It has a rating in minutes and every hole through it has to maintain that rating.
- Know the difference between the two product types.Intumescent products expand many times in heat to close a gap left when something inside it melts or burns away — used around plastic pipes, cables and combustible services. Fire-resistant sealants simply resist burning through and are used in gaps where nothing will disappear. They are not interchangeable.
- Understand that it is a tested system, not a product.A fire-stopping detail is tested as a complete assembly: this sealant, at this depth, with this backing material, in this wall construction, around this service. Using the same tube at half the depth, or with the wrong backing, or in a different wall, is untested and unrated.
- Never use ordinary foam or sealant in a fire-rated opening.Standard expanding foam has no fire performance at all and burns readily. Ordinary silicone and acrylic offer nothing. A gap around a pipe through a compartment wall filled with builder's foam is a fire path, and it is a common and serious defect.
- Recognise where you are in regulated territory.Any penetration through a compartment wall or floor, anything in the common parts of a block of flats, anything affecting a protected escape route, and any work subject to building regulations. In those, the work has to be done to a tested detail and documented — and in a block of flats it is the building owner's responsibility, not yours.
- Distinguish acoustic sealant, which is a different product entirely.Acoustic sealants are flexible mastics used to seal air paths in partitions for sound rather than fire. They look similar, they are sold alongside, and they have no fire rating unless it is separately stated.
- Report defects rather than fixing them yourself in shared buildings.If you can see a hole through a compartment wall in a block of flats — around new cabling, a soil pipe, a boiler flue — that is a matter for the freeholder or managing agent, who has a legal duty about fire safety in the common parts. Filling it yourself with the wrong material makes the record worse, not better.
- Keep the paperwork if you do have it done.A specialist installer provides a certificate identifying the system used at each penetration. That documentation is what a building control officer, a fire risk assessor and a buyer's solicitor will ask for.
Tips
- Fire-rated expanding foam exists and is sold alongside ordinary foam in almost identical cans. Read the can — the difference is not visible in the cured foam and it matters enormously.
- A downlighter cut into a fire-resisting ceiling needs a fire-rated fitting or a fire hood, which is the same principle in a different product.
- New cabling and new plumbing are the commonest cause of new holes through compartment walls. If a trade has run services through a wall between a garage and a house, or between flats, ask how the penetration was sealed.
- The guidance that governs this is in the building regulations documents for your nation and in the manufacturers' tested details. Both change; check the current version rather than an old article.
- An intumescent product has a shelf life like any other sealant, and an out-of-date one may not perform as tested.
Questions people ask
Can I use fire-rated sealant myself?
For a simple gap in your own house that is not a regulated penetration, yes, using the manufacturer's stated detail. For anything through a compartment wall or floor, in a flat, or subject to building regulations, it is specialist work that has to be documented.
What is the difference between intumescent and fire-resistant?
Intumescent expands in heat to close the gap left when something inside it burns or melts away, so it is used around plastic pipes and cables. Fire-resistant simply does not burn through, and is used where nothing will disappear.
Is ordinary expanding foam fire-rated?
No. Standard polyurethane foam has no fire performance and burns. Fire-rated foam is a separate certified product and the cans look very similar, so read the label.
Who is responsible for fire-stopping in a block of flats?
The building owner or the responsible person under fire safety law, for the common parts and the compartment construction. If you find an unsealed penetration, report it to the managing agent in writing rather than filling it yourself.