Intumescent coatings
An intumescent coating is a paint-like layer that swells into a thick insulating char when heated, keeping structural steel below the temperature at which it loses strength, or slowing the spread of flame over timber. The thickness needed depends on the steel section, the fire rating and the product’s test data.
Applied prices depend mainly on the fire rating, the steel sections and whether the coating goes on in the fabrication shop or on site, so it is priced against a steel schedule rather than a flat rate per square metre.
- Sheet
- PF-08
- Subject
- Intumescent coatings
- Scope
- England, Scotland, Wales
- Prices read
- November 2026
PF-08.1
When intumescent coating is used
- New structural steel needs 30, 60, 90 or 120 minutes of fire resistance.
- Existing coating is damaged, flaking or was never applied to the right thickness.
- Exposed steel is wanted as a visible feature without boards.
- Timber in escape routes needs a better surface spread of flame class.
- A change of use raises the fire rating the structure needs.
- A survey cannot confirm what coating, if any, is on the steel.
PF-08.2
What intumescent coating costs
| Item | Published figure |
|---|---|
| Low ratings, 30 to 60 minutes Thin-film coatings, often a single visit on site | Lowest cost per m² |
| Survey of existing coatings Dry film thickness readings and condition | Priced after a site visit |
| Higher ratings, off-site application 90 and 120 minutes, or applied in the fabrication shop | Priced to the steel schedule |
Where these figures come from
Coating cost rises with the rating, because the required thickness rises with it, and with the section factor of each member: lighter, thinner sections need more coating than heavy ones for the same rating. Off-site application in the fabrication shop is usually cheaper and better controlled than on site. Read November 2026. The passive fire protection cost guide explains what drives the price.
PF-08.3
What a sound coating specification covers
The parts of the job that decide whether it holds up in a fire.
A steel schedule
Each member with its section size, its fire rating and its section factor, which sets the thickness needed.
The product and its data
The coating named, with test data showing it covers those sections, ratings and the limiting temperature for your design.
Thickness to be applied
The dry film thickness for each member, and how it will be measured and recorded.
Surface preparation and primer
Cleaning, the primer, and whether it is compatible with the coating. Incompatible primers are a common failure.
Topcoat and conditions
Whether a sealer or topcoat is needed for humidity or exposure, and the temperature and humidity limits for application.
Records you can keep
Photographs of every item before and after, a unique reference or label for each, and a schedule you can hand to the next fire risk assessor or put in the golden thread.
Have steel to protect or old coating to check? Send the job over and get it priced.
Find a contractorPF-08.4
How a coating job runs
Steel schedule
Sections, ratings and section factors listed from the structural drawings.
Specification
Product and thickness set for each member.
Preparation
Surfaces cleaned and primed; existing coatings tested if over-coating.
Application
Coats built up to thickness, measured as work goes.
Records
Thickness readings for each member handed over.
PF-08.5
Questions people ask
How does intumescent coating work?
When heated it swells many times its applied thickness into a char that insulates the steel or timber underneath, slowing how fast it heats up so the structure keeps its strength for the rated time.
How long does intumescent coating protect steel?
Coatings are commonly specified for 30, 60, 90 or 120 minutes. The rating depends on the product, the thickness applied and the steel section. Thin-film coatings are typical up to 60 or 90 minutes.
Can intumescent paint be applied over old paint?
Only over a primer or coating the maker confirms is compatible. Otherwise the old coating must come off. A test patch and adhesion check are usual.
What does intumescent coating cost per m²?
It depends on the rating, the steel sections and access. A 30 or 60 minute thin-film coating applied in the fabrication shop costs least; 90 and 120 minute ratings need much thicker coats and cost substantially more per m². Price it against a steel schedule listing each member, its section factor and its rating.
Is intumescent paint the same for timber?
No. Coatings for timber mostly improve surface spread of flame classification, while coatings for steel are designed to keep load-bearing members cool. Use a product tested for the material and the result you need.
Who checks the coating has been applied properly?
The applicator should measure and record dry film thickness for each member. Some clients appoint an independent inspector, and some installers hold third-party certification for coating application.
Find an intumescent coating applicator
Three short steps: where the building is, what the job is, and how to reach you. It takes about two minutes.
This is a free matching service, not a passive fire protection contractor. We find one who covers your area and name them to you first. Nobody contacts you until you say yes.
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- Within one working day we will email or call to tell you which passive fire protection contractor covers your area.
- Your details reach that firm only if you say yes.
- They look at the site and give you a fixed price. No marketing from us, ever.