Fire-rated silicone sealants are specialist products engineered to prevent fire and smoke from spreading through gaps, joints, and service penetrations in buildings. Unlike standard silicone, they're part of a tested fire protection system. UK buildings must comply with Approved Document B of the Building Regulations — most recently updated in 2025 — which sets out where and how these products must be installed.
Most people don't think much about sealant — and why would they? It's the unsung trim of any decent fit-out. But when it comes to fire safety, the type of sealant used and how it's applied can genuinely be the difference between containing a fire and allowing it to spread unchecked through a building.
Fire-rated silicone sealants are a non-negotiable part of passive fire protection in commercial and residential buildings across the UK. Whether you're managing a refurb, specifying a new build, or just trying to make sure your premises are legally compliant, understanding what these products do — and where they must go — matters more than most people realise.
We've been working with silicone sealants for over 40 years, covering everything from straightforward domestic jobs to complex commercial projects across Kent, London, Derby, and the South East. Here's what we think every facilities manager, building owner, and contractor ought to know.
What are fire-rated silicone sealants (and what aren't they)?
Fire-rated silicone sealants are specialist products designed to resist or actively respond to fire and smoke, forming part of a tested firestopping system. They are not the same as standard construction or sanitary silicone.
Let's clear something up straight away: not all silicone is created equal.
The standard silicone you'd use around a bath or window frame has no meaningful fire resistance. It softens and breaks down under heat, leaving gaps wide open for fire and toxic smoke to travel through. Fire-rated silicone sealants, by contrast, are specifically engineered to maintain their integrity — or actively respond — when temperatures rise.
Many fire-rated products are intumescent, meaning they expand significantly when exposed to heat. This expansion is what does the work: it fills gaps that open up when materials like plastic pipes or cable insulation melt away, maintaining the seal when it's needed most. Importantly, intumescent sealant doesn't expand on application — it remains flexible and cured until a fire event triggers that heat-activated response.
Worth knowing: "Fire-rated" doesn't mean fireproof. These products are part of a tested system — one that includes substrate type, joint geometry, and application method. A fire-rated sealant used incorrectly, or in the wrong configuration, may not perform to its rated classification. One product also doesn't suit every gap — always check the tested system, not just the product label.
Products should carry a UKCA mark (or CE marking where still applicable) and be tested in accordance with recognised standards such as BS 476-22 or BS EN 1366-4. Third-party certification schemes including CERTIFIRE and BM TRADA Q-Mark provide additional assurance that a product performs as claimed — and that manufacturing consistency is independently audited.
How does fire-rated sealant support fire resistance, fire protection and compartmentation?
Fire-rated sealants maintain the integrity of fire-resisting compartments by sealing gaps, joints, and penetrations that would otherwise allow fire and smoke to pass between zones. Without them, even a correctly constructed fire-rated wall or floor can fail.
Compartmentation is the principle at the heart of passive fire protection. Put simply, it divides a building into separate fire-resistant zones, each designed to contain fire and smoke for a defined period — typically 30, 60, or 120 minutes — although some fire-rated sealant systems can offer passive fire protection for up to 4 to 5 hours depending on joint configuration, with performance set by tested integrity ratings.
The problem is that every building is full of potential weak points: the gaps around pipes passing through a wall, the edge joint between a floor slab and a façade, the linear seam where two fire-rated boards meet. Any of these, left unsealed or sealed with the wrong product, can undermine an otherwise robust compartment.
Smoke sealing is just as important as fire sealing. Toxic smoke inhalation is responsible for the majority of fire fatalities, and it travels fast. Even small gaps around service penetrations can allow smoke to migrate into escape routes long before flames arrive and prevent a gas tight seal from doing its job to protect adjacent areas.
Under the Building Safety Act 2022, accountability for ensuring firestopping is correctly installed and maintained has been significantly strengthened. "Dutyholders" — including contractors, building owners, and facilities managers — now carry explicit responsibility for ensuring fire protection elements, including sealants, are installed as tested and remain compliant over the building's lifetime.
When are fire-rated silicone sealants essential in UK buildings?
Fire-rated sealant is required wherever a gap, joint, or service penetration passes through or along a fire-resisting element — including walls, floors, and ceilings. This applies to both new builds and refurbishment projects.
There's no one-size-fits-all answer, but several common building scenarios consistently call for fire-rated sealants:
Service penetrations — where pipes, cables, conduits, or cable trays pass through fire-rated walls or floors. This is one of the most common areas we're called in to address, particularly on refurb projects where new services have been added and the penetration seals weren't updated.
Linear joints — wall-to-floor junctions, perimeter gaps, slab edges, and curtain wall interfaces where two elements of a fire-rated construction meet.
Movement joints — joints designed to allow thermal or structural movement, which need a fire-rated sealant with appropriate flexibility.
Plant rooms and service risers — high-risk areas where multiple service routes converge and compartmentation is critical.
Escape routes and corridors — any penetration or joint that could allow fire or smoke to compromise a means of escape needs proper fire-rated sealing.
For businesses operating in commercial premises, compliance with the UK's Building Regulations — specifically Approved Document B, which received updated amendments in 2025 — isn't optional. Using the right fire-rated silicone sealants for businesses, installed correctly, is part of meeting that duty.
Choosing the right fire-rated silicone sealant: a practical checklist
The right fire-rated sealant depends on the required fire resistance period, the substrates involved, joint dimensions, and whether the penetration includes combustible materials. Always select a fully tested system, not just a sealant product in isolation.
This is where things get technical, but it doesn't have to be complicated. Here's a straightforward checklist:
Required fire resistance period — match the sealant's tested classification (e.g., 30, 60, or 120 minutes) to what the specification calls for
Substrate compatibility — concrete, plasterboard, and metal all behave differently; confirm the sealant bonds properly to your substrates. Some products adhere to most substrates without priming and are non corrosive to metals.
Joint width and depth — products are tested within specific dimensional parameters; some tested systems may be approved to seal gaps up to 50mm wide, but only within the stated test parameters
Movement capability — does the joint flex? If so, you'll need a product rated for that movement; where tested, fire-rated silicone sealants can offer high elasticity with movement capability in the ±25% to ±50% range
Service type — intumescent sealants are essential where plastic services may melt; non-intumescent products may suit static joints with no combustible penetrations and can be ideal for sealing, bonding, and glazing applications across many building elements where the tested system allows. Put simply: intumescent silicone sealant is better suited to cable and pipe penetrations where materials could burn away and leave a gap, while non-intumescent fire-rated sealant works best for static, inorganic joints where no such risk exists
Environment — some sealants are suited to interior use only; external applications and wet environments require different formulations. Some use a neutral curing system that is practically odourless or odourless, which can make them more suitable for interior use.
Certification — always check the full system is tested and certified (UKCA/CE marked, CERTIFIRE or BM TRADA Q-Mark where available), not just the sealant in isolation, and confirm paintability, including compatibility with water based and solvent based paints, on the datasheet
Some products are supplied ready-to-use in standard cartridges and come in white, grey, black, or clear depending on the range.
If you're unsure what specification or rating applies to your project, we're happy to talk it through.
Installation: why "good stuff, badly fitted" still fails
Even the best fire-rated silicone sealant won't achieve its rated classification if it's been applied incorrectly. Surface preparation, correct joint sizing, and full substrate contact are all critical to performance, and curing times also affect installation quality.
We see this regularly on remedial jobs — a technically compliant product, undermined by shoddy installation.
Key installation principles include:
Surface preparation — substrates must be clean, dry, and free from dust, grease, or old sealant residue before anything goes on
Correct joint sizing — backing materials should be used to control the depth-to-width ratio; a joint that's too deep or too shallow can compromise performance
Full contact — the sealant must bond fully to both sides of the joint without voids or bridging
Neat tooling — not just cosmetic; proper finishing ensures the sealant fills the joint profile correctly
Skin and tack times — a typical skin forming time is 15–30 minutes at 23ºC, and tack free time is 120 minutes at 23ºC, but always confirm the exact product datasheet
No painting over — applying paint or filler over an intumescent sealant can prevent the heat-activated expansion from occurring, effectively disabling the product's fire protection
We take real pride in the quality of our finish, and on fire-stopping work that's doubly important. A clean, well-applied bead is much easier to inspect, document, and sign off. It also doesn't leave anyone guessing.
Rectifying old or failed sealant is something we carry out regularly. If there's existing fire-stopping in place that's cracked, delaminated, or simply the wrong product, it needs to come out and be replaced properly — not just topped up.
Common mistakes we see (and how to avoid them)
A few recurring issues we encounter, especially on refurb and fit-out projects:
"Silicone is silicone" — using standard sanitary or construction silicone in a fire-rated application because it looks the same. It isn't. The consequences can be serious.
Poor prep — skipping priming on difficult substrates, or applying sealant to damp or dusty surfaces.
Painting over fire-rated sealant — a surprisingly common one. Covering intumescent sealant with paint or filler prevents it from activating under heat, which defeats the point entirely.
No documentation — completing the physical work but failing to record product batch numbers, certification references, or photographic evidence. This creates real problems at handover or during a future audit.
Gaps hidden by finishes — service penetrations sealed after decoration, where it's impossible to tell whether the correct product was used or whether the void is fully filled.
Mismatched systems — combining products from different tested configurations that haven't been validated together.
Quick checklist for site managers and building owners
Before signing off any fire-stopping work, run through these:
All fire compartments and penetrations identified and marked on drawings
Specification confirmed (required fire rating, substrates, service types)
Tested system selected — not just a product, the full configuration
Installation carried out by competent, experienced operatives
Photographs taken of completed work prior to concealment
Product data sheets, batch numbers, and certifications filed
Documentation included in O&M/compliance handover pack
FAQs
What's the difference between fire-rated silicone and intumescent sealant?
Fire-rated silicone maintains its physical integrity at high temperatures. Intumescent sealant — which can also be silicone-based — goes further by expanding under heat to seal gaps created when adjacent materials burn or melt. Many fire-rated silicone products incorporate intumescent properties, but not all do.
Do I always need an intumescent silicone sealant?
Not necessarily. Intumescent products are most important where combustible services like plastic pipes or cable insulation run through the penetration. For static joints with no combustible elements, a non-intumescent fire-rated sealant may be appropriate — though always check the tested system requirements.
Where is fire-rated sealant required in UK buildings?
Approved Document B of the Building Regulations requires that any penetration or joint in a fire-resisting element — wall, floor, or ceiling — must be sealed to maintain the required fire resistance. This applies to commercial and residential buildings, including offices, blocks of flats, hospitals, schools, and industrial premises.
Can I use fire-rated sealant in bathrooms or kitchens as well?
Some fire-rated silicone sealants are moisture-resistant and suitable for wet areas. However, not all are — always check the product datasheet. If the joint is in a fire-rated element within a wet room, the sealant must meet both the fire performance and the environmental requirements.
How long does fire-rated silicone sealant last?
With correct installation, high-quality fire-rated sealants can perform reliably for many years — some manufacturers suggest working lives of 25 years or more. That said, periodic inspection is important. Movement, building settlement, or damage can affect integrity over time, and any compromised sealant should be replaced promptly. Fire doors and firestopping seals should generally be inspected every 6–12 months depending on building type and usage.
What should I ask for as proof of compliance?
Ask for: product data sheets and fire test classification reports, confirmation of the tested system used, photographic evidence of installed work, and product batch numbers for traceability. This documentation is essential for compliance packs and future audits.
Can you replace or rectify old or failed fire-rated sealant?
Yes — this is something we do regularly. Remedial fire-stopping work involves removing failed or non-compliant sealant, preparing the substrate correctly, and applying the right product to the tested specification. Drop us a photo of the joint or penetration in question and we can advise quickly.
Do you work on commercial projects outside Kent, London, and Derby?
Our core coverage spans Kent, London, Derby, and the South East, but we do travel further for the right project — including international works on request. Get in touch and we'll let you know what's possible.
Get it right from the start
Fire-rated silicone sealants aren't complicated in principle: use the right product, in the right configuration, installed correctly, and document the lot. Where it goes wrong is usually down to a shortcut somewhere in that chain.
We're a family-run business with over 40 years of hands-on experience across commercial and domestic sealant work, and fire protection is one of the areas we take particularly seriously. We cover Kent, London, Derby, and the wider South East — and for the right project, further afield too.
Whether you're working on a new build, a refurb, or you've got existing sealant that needs assessing or replacing, we're happy to have a conversation. Send us details or photos of the job and we'll point you in the right direction.
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