Intumescent and Fire-Rated Paints for London Properties: A Practical Guide
Where intumescent and fire-rated paints are required in London properties, how they work, product options including Nullifire, Flame Guard and Leighs, and the specification and building regulations process.
What Is Intumescent Paint and How Does It Work
Intumescent paint looks and applies much like a standard decorative finish, but it contains a chemical compound that reacts when exposed to elevated temperature. When the surface reaches approximately 150–200°C, the intumescent layer expands — typically to ten to fifty times its applied thickness — creating a carbonaceous foam char that insulates the substrate from heat. This char is what provides fire resistance: it dramatically slows the temperature rise in the steel, timber or other substrate below, maintaining structural integrity or maintaining compartmentalisation for a defined period — typically 30 or 60 minutes.
The expansion mechanism means intumescent paint does not prevent a fire from occurring, nor does it make a surface non-combustible. What it does is buy time: time for occupants to evacuate, for sprinkler systems to suppress, and for fire services to arrive and intervene.
Where Fire-Rated Paint Is Required in London Properties
Structural steelwork in residential and commercial properties in London increasingly uses exposed steel beams and columns — a common feature in basement extensions, loft conversions, and warehouse-to-residential conversions in areas like Bermondsey, Hackney and Battersea. Exposed steel loses structural strength rapidly in fire — unprotected structural steel can reach critical temperature within five to ten minutes of exposure to a standard fire curve. Building Regulations Approved Document B requires structural steel to achieve a minimum fire resistance period of 30 minutes (in most residential applications) to 60 or 90 minutes in commercial or multi-storey settings.
Intumescent paint on structural steelwork is the most architecturally sympathetic protection system — it allows the steel to be left exposed or decorated in a topcoat of the client's choice, unlike boarding or sprayed-on fireproofing which covers the steel entirely.
Fire doors in HMOs, apartment blocks, purpose-built flats and converted houses in multiple occupation are required under the Regulatory Reform (Fire Safety) Order 2005 and the Housing Act 2004. A fire door must maintain its integrity for a specified period (typically FD30 — 30 minutes — for internal doors in most residential settings, FD60 for specific applications). The door assembly includes the door leaf, frame, ironmongery, intumescent strips and smoke seals. The paint applied to a fire door must not compromise its tested performance — and non-approved paints applied over a specified fire door can invalidate its certification.
Stairwells and escape routes in apartment buildings, HMOs and commercial properties are subject to requirements for surface spread of flame (Class 1 or Class 0 under BS 476 / Euroclass B or C under EN 13501). In practice this means that wall and ceiling finishes in common areas, stairwells and corridors in multi-occupancy buildings must meet a defined flame-spread rating — standard vinyl emulsion does not automatically satisfy this, and a tested Class 1 or Class 0 finish must be specified.
Product Guide
Nullifire SC902 is the benchmark intumescent paint for structural steelwork. It is a water-based, single-pack solvent-free product designed for use on primed steelwork. At a specified dry film thickness, SC902 provides 30- or 60-minute fire resistance in accordance with BS EN 13381-8. It can be overcoated with most decorative finishes. Nullifire provides full technical data sheets and fire performance certificates for specification and building control submission.
Leighs Paints Firetex range (particularly FX5100 and FX6002) are widely used on both structural steel and fire doors in London commercial and residential projects. Leighs Firetex FX5100 is a water-based thin-film intumescent suitable for external or internal structural steel, tested to BS EN 13381-8 for both cellulosic and hydrocarbon fire curves. The Leighs technical support team can assist with thickness calculations for specific member sections, fire resistance periods and section factors.
Flame Guard (available through various specialist fire protection suppliers) is a water-based intumescent paint commonly specified for internal timber elements — fire doors, timber structural members in loft conversions, and timber-framed roof structures where fire stopping is required. Flame Guard products include BS 476 Part 6 and Part 7 tested formulations suitable for Class 1 spread of flame compliance on walls and ceilings.
Zinsser Perma-White and similar products marketed as 'fire retardant' emulsions are appropriate for the flame-spread rating requirement on walls and ceilings in common areas (they achieve Class 1) but must not be confused with structural intumescent coatings. They do not provide any structural protection to steelwork or improve the fire resistance period of a fire door.
Specification and Building Regulations Compliance
The specification of intumescent coatings for structural steelwork is a technical process, not a decorating decision. The fire resistance required depends on the occupancy type, the floor-to-floor height, and the specific structural member's section factor (the ratio of heated perimeter to cross-sectional area — a measure of how quickly the section heats up). Section factor and required fire resistance period together determine the dry film thickness of intumescent coating required.
For most residential projects in London, the structural engineer will specify the required fire resistance period in the structural drawings. The intumescent paint contractor (or a decorator working to a fire protection specification) then calculates the required DFT using the paint manufacturer's published data tables. An independent fire inspector or approved inspector appointed by the local building control authority will typically inspect the work, and the contractor must provide a certified record of DFTs achieved — measured with a film thickness gauge on cured product.
We strongly recommend that any intumescent coating project on structural steel is overseen by someone with appropriate CSCS or NVQ qualification in passive fire protection. For fire door painting, always confirm that the paint system being used is compatible with the door's fire certification before applying.
Landlord Compliance: HMOs and Purpose-Built Flats
London has a very high volume of HMO properties, and fire safety compliance is one of the principal areas of risk for landlords. A competent licensing inspection will check fire door condition, intumescent strips, smoke seals, and in some cases the surface spread of flame of wall and ceiling coatings in common areas. Repainting common areas with a Class 1 rated product (rather than standard vinyl emulsion) is a straightforward compliance measure that significantly reduces risk.
We apply fire-rated coatings in common areas, stairwells and on fire doors as part of our standard HMO decoration service.
Talk to Us About Fire Protection Coating
Whether you have structural steel that needs specifying or a block of flats with common areas due for redecoration, we can help with product selection, specification support, and application.
Contact us or request a free quote — we work across London on residential, HMO and commercial fire-rated decoration projects.