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A paint that becomes insulation
An intumescent coating is a passive fire protection product applied to structural steel like a paint. At normal temperatures it is a thin film – typically a few tenths of a millimetre to a few millimetres thick. When heated in a fire, it reacts and expands into a thick, porous carbon char that insulates the steel.
The purpose is not to stop the fire but to slow down the heating of the steel, so that beams and columns keep their load-bearing capacity for the time the building code requires – 30, 60, 90, 120 minutes or more.
The coating system
- Primer – anti-corrosion primer approved by the intumescent manufacturer.
- Intumescent basecoat – the fire protective layer, applied to the thickness required for each member.
- Topcoat – colour and protection against humidity or exterior exposure where the system requires it.
Primer and topcoat are part of the tested system. Using an unapproved primer or topcoat can invalidate the fire performance.
Main types
| Type | Typical use |
|---|---|
| Water-based thin film | Dry interiors, occupied buildings, low VOC |
| Solvent-based thin film | Shop application, humid climates, semi-exposed areas with topcoat |
| Epoxy (thick film) | Long cellulosic ratings, exterior and industrial steel, hydrocarbon fires |
Where it is used
Intumescents are the preferred fire protection for exposed and architectural steel – atriums, airports, offices, shopping centres – because the shape of the steel stays visible. They are also widely used for shop-applied export steel, because the members arrive on site already protected.
What it is not
- It is not a fire retardant for combustible materials.
- It does not have one thickness per rating – the thickness depends on each member.
- It is not interchangeable between products – each product has its own certified data.
FAQ
Is intumescent paint the same as fire retardant paint?
No. Fire retardant paints reduce flame spread on combustible surfaces; intumescent coatings insulate structural steel to maintain its fire resistance.
How long does intumescent coating protect steel?
For the rating it was designed for – the thickness is chosen per member to achieve 30 to 120 minutes or more, according to the product's approved data.
Preliminary calculations are provided for estimation purposes only. Final coating thickness and fire protection system selection must be verified against the approved product documentation, applicable project requirements and relevant engineering assessments.