fireproof paint for steel

Why you need fireproof paint for steel

Strength is one of the main reasons we use steel in building construction. Steel is a tough construction material, used in buildings across the country from the Birmingham Bullring to Canary Wharf. However, this strength is challenged by the severe heat of a fire. In a fire, it can take only minutes for unprotected steel to reach critical failure temperatures of 550ºC, at which point it loses its load bearing capacity, leading to structural collapse. In fact, above 300ºC steel begins to lose strength. Which is why you need a fireproof paint for steel.

Fireproof paint for steel can provide the following advantages:

  • Fire protection for up to 120 minutes
  • Preventing structural collapse
  • Allowing firefighters more time to get the fire under control
  • Extending crucial evacuation time

In this article we outline the different types of fire protection coatings, how to comply with building fireproofing regulations, and where to find fireproof paint for steel products and contractors in the UK.


The 2 types of fireproof paint for steel

Fireproof paint can be classified by fire protection method: intumescent or fire retardant. Each of these coating types are further divided by the length of time they provide fire protection for – 30, 60, 90, or 120 minutes. Building regulations require different minimum time requirements which vary depending on building type. You can read more about this subject in our general passive fire protection article.

  1. Intumescent paint: Intumescent paints protect their steel substrate by providing an insulating layer between steel and the fire. Exposure to the heat of a fire triggers a reaction, causing the intumescent paint to expand to up to 50 times its thickness and form a solid foam-like char. This char insulates the steel from the heat, so keeping it below the temperatures that would compromise it. Intumescent paint is the main coating used for steel.
  2. Fire retardant paint: A fire retardant paint for steel works by releasing a fire-damping gas when heated, which prevents the spread of flame across a surface – usually walls and ceilings. It is less common to use fire retardant paints for steel structures, because they do not have the same insulating properties of intumescent paint.

For the most comprehensive fireproof paint system, you can use these two paints together, with fire retardant paint for steel as a top coat over intumescent paint. In this case, the flame retarding action prevents the intumescent paint from triggering, adding vital extra time.

Application of fireproof coatings for steel: thin and thick film

Fireproofing coatings can be divided into two broad families: thin film and thick film. Thin film materials are either solvent based or water based and are mainly used for building fires. Thick film coatings were originally developed for the off-shore and hydrocarbon industries but have been modified for use in buildings.

Fireproof paint for steel is applied by brush, spray or roller.

Fireproof paint for steel is applied by brush, spray or roller.

Thin film fire paint for steel

Thin film fireproofing coating systems for steel generally have three components, a primer, a basecoat, and a sealer coat. These paints are mainly used for 30, 60, and 90 minutes. Thin film materials have a 50:1 expansion ratio; a 1mm thick coating will expand to about 50mm in a fire. These coatings are bother solvent- and water-based, and are available in a range of finishes.

Thick film fireproof coating for steel

Thick films have a higher dry film thickness than thin film coatings, and are usually epoxy based. Originally developed for use with hydrocarbon fires, thick film materials are now also used in harsh or difficult to maintain environments where thin film materials would not work. Examples include external steel in high rise buildings and exposed marine environments. Expansion ratios are typically about 5:1, and attractive finishes are also possible.


Where to find steel fireproof paint for steel products & contractors in the UK

There are many fireproof paint for steel products available on the UK market. AkzoNobel, Jotun, Bollom, and Thermoguard all have intumescent ranges. The table below describes several of the products available. Prices and coverages are indications only, and coverage and fire resistance are dependent upon correct application. If you would like any more information regarding fireproofing steel, or would like to be connected with one of our partners for your project, contact us! Our experts are here to help, just use the “Request a quote” button at the bottom of this article and take advantage of our 100% free quote service.

Fireproof Paint for Steel ProductDescriptionMaximum Fire ResistancePriceCoverage
Bollom Brosteel Ultra 60 Fire ProtectionThin film intumescent for internal structural steelwork60 minutes£180-190/10L1m2 per L for 2 coats
International InterChar 1120Thin film intumescent coating designed for onsite application to interior exposed structural steel120 minutes£500-550/20L1m2 per L
Jotun Steelmaster 60WBIntumescent basecoat for fire protection of structural steel60 minutes£40-50/5L1m2 per L
Thermoguard Thermocoat WThin film intumescent paint system providing fire resistance to structural steel90 minutes£90-100/5kg1.5m2 per kg
Thermoguard Flame Retardant TopcoatFlame retardant paint finish for use over Thermocoat W to protect, decorate and complete the fire protection systems Class 1 and Class 0 protection£90-100/5L8m2 per L

Understanding your fireproofing needs and regulations

According to British Standards, materials (including paints) are classified based on the rate at which they allow flame to spread under test conditions. These classes go from Class 1 (the best) to Class 4 (the worst). Class 1 requires that the surface allows flame to spread no further than 165mm from the point of ignition over a period of 10 minutes, under test conditions.

The Building Regulations added another classification to reflect the fact that restricting the danger of fire is not just about preventing the spread of flame but also about heat. Fire propagation (or the amount of heat added to a fire by burning materials) is an important factor in fire spread and intensity. This extra class, Class 0, includes the requirements for Class 1, but also that the material has a very low fire propagation index.

The decision whether your fireproof paint for steel should meet Class 1 or Class 0 classification is usually determined by your Building Regulations Officer or Architect.

Once your fire paint for steel is applied, you should obtain a certificate to show you have complied with all relevant regulations and used the correct protective surface coating. If you do not obtain the correct certificate(s) then, in the event of a fire, you may be held liable and prosecuted.

The minimum period of fire resistance of a ground or upper storey in a sprinklered building, based on the height of the top floor above ground.
Building TypeNot more than 5mNot more than 18mNot more than 30mMore than 30m
Residential30 minutes60 minutes90 minutes120 minutes
Office30 minutes30 minutes60 minutes120 minutes
Shop and Commercial30 minutes60 minutes60 minutes120 minutes
Assembly and Recreation30 minutes60 minutes60 minutes120 minutes
Industrial30 minutes60 minutes90 minutes120 minutes