Painting Fire Doors: Why Standard Paint Fails and What to Use Instead

Why Fire Doors Are a Special Case

A fire door is a tested, certified assembly. The door leaf, frame, intumescent strips, hinges, and ironmongery all contribute to the rated performance — typically FD30 (30 minutes integrity) or FD60 (60 minutes) — and changing any element of the assembly, including the paint system applied to it, can invalidate that rating.

This is not a theoretical concern. In the aftermath of the Grenfell Tower fire, the scrutiny of building safety in HMOs, blocks of flats, and houses in multiple occupation has increased enormously. Local authority inspectors, building control officers, and fire risk assessors are now far more likely to flag inappropriate decoration of fire doors as a deficiency. In the worst cases, it means a door that no longer meets its declared fire rating in the event of a fire.

How Paint Affects Fire Door Performance

The mechanism is straightforward. Most fire doors achieve their integrity rating partly through the compression of intumescent strips around the door leaf perimeter. These strips expand dramatically when exposed to heat (typically from around 150–200°C), sealing the gap between door and frame to prevent passage of fire and smoke.

If the paint system applied to the door is too thick, it can:

• Interfere with the action of the intumescent strips by bridging the gap between door and frame
• Add a flammable fuel load to the surface of the door
• In some cases, affect the dimensional tolerance of the door leaf within the frame, preventing correct closure

The total paint film thickness on a fire door is therefore not just an aesthetic question. BS 8214:2016 (the code of practice for timber-based fire door assemblies) recommends that paint film build-up be considered in the context of the door's certification, and that manufacturers' guidance on acceptable finishes be followed.

What the Certification Means in Practice

Fire doors are tested and certified as complete assemblies, typically to BS EN 1634-1. The certification includes the test door leaf, frame, and finishing system. When a door manufacturer issues a certificate, it may specify:

• Maximum permitted paint film thickness (often 100–150 microns DFT)
• Permissible paint types (water-based or solvent-based, and in some cases specific product approvals)
• Whether intumescent strips were included in the tested assembly

For doors certified under a third-party scheme such as BWF (British Woodworking Federation) CERTIFIRE or TRADA Q-Mark, the certification record will indicate what finishes are compatible. If you cannot access the original certification for a door in a block or HMO — which is frequently the case with older stock — the safest approach is to consult the door manufacturer directly or specify a paint system that has been independently tested for compatibility with fire door assemblies.

Which Paint Systems Are Appropriate

For most FD30 and FD60 doors in residential and commercial buildings, a water-based eggshell or satinwood applied within appropriate film thickness limits is acceptable. The key products used by professional decorators on fire doors include:

Dulux Trade Diamond Eggshell — a water-based, low-odour product that dries to a hard, washable finish. Applied in two coats, the DFT is typically within acceptable limits for most fire door certifications.

Zinsser AllCoat (water-based) — a primer and topcoat in one, useful for tight programme situations where a one-coat system is needed. Check the DFT against the door manufacturer's guidance.

Teknos Aquatop 2800 — widely specified in commercial and multi-residential projects, with good durability and compatibility documentation available from the manufacturer.

What should not be used: thick-bodied gloss systems applied over existing paint build-up without checking total DFT; masonry paint (obviously wrong, but it does happen); or any product applied without knowledge of what is already on the door.

Checking Existing Paint Build-Up

On doors in older blocks of flats or HMOs that have been redecorated multiple times, existing paint build-up may already be close to or exceeding acceptable limits. A paint thickness gauge (available from specialist tools suppliers) can measure DFT non-destructively; alternatively, a cross-cut into the existing finish at a discreet location will reveal the number of layers.

If the existing build-up is excessive, options are: full strip-back to bare wood (appropriate where certification requires a fresh start), or mechanical stripping of the bulk of the existing finish followed by a fresh system from bare. Chemical stripping is less appropriate on fire doors as it can affect the integrity of intumescent strips if they are exposed to stripper.

Common Mistakes in HMOs and Blocks

The most frequent errors we see when surveying fire doors in London rental properties:

1. Painting over intumescent strips — the strips must remain unobstructed. Mask them during painting, or replace them after painting if they have been contaminated.
2. Using the wrong product — oil-based gloss applied in multiple coats without checking DFT or certification compatibility.
3. Not rehanging properly after painting — a door hung with clearances reduced by paint build-up on the rebate will bind and not close properly, defeating the purpose of a fire door.
4. Painting self-closing devices — the pivot or arm of a fire door closer must not be painted over. It will seize.

Your Responsibilities as a Landlord or Managing Agent

Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person for a multi-occupied residential building (typically the landlord or managing agent) is required to ensure that fire doors are properly maintained. Specifying an inappropriate paint system, or allowing a contractor to apply one, is a breach of that duty.

Get the specification right from the start, keep records of the products used and the dates of application, and include fire door decoration in your periodic fire risk assessment review.

If you manage properties in London and need a contractor who understands fire door painting requirements, contact us or request a free quote.