What Is Intumescent Heat-Resistant Paint? (and the Best Brands for Steelwork)

What Is Intumescent Heat-Resistant Paint? (and the Best Brands for Steelwork). Author - Andy Potts October 6th 2020 (reading time 5 mins)


heat resistant paint

heat resistant paint on steel

(Heat Resistant Coatings - Displayed as a cutaway on a substrate)

Intumescent heat-resistant paint provides an efficient and cost-effective method of protecting structural steel, timber, concrete and composite elements against fire damage. It is widely used in the steel fabrications, construction, marine and aerospace industries as a passive heat protection system that complies with building regulations requirements for fireproofing.

This article provides an overview of:

  • The properties of this type of heat-resistant paint
  • Its role in building regulations compliance
  • How to apply it correctly to steelwork
  • The best brands on the market

What is intumescent heat-resistant paint?

Intumescent paint is a specialist protective coating that expands (intumesces) when exposed to temperatures above 120øC. For this reason, it is also known as reactive paint, and fire-resistant paint. It is not the same as high-temperature heat-resistant paint such as Jotan Resist, Jotan Solvalitt  and Ultrimax Ultritemp. These coatings are designed to be used on metal items such as metal chimneys, exhausts, furnaces and chimineas that get very hot and need to be protected from corrosion.

How does it work?

When structural materials reach a critical temperature in a fire, they lose their load-bearing capacity and collapse. An intumescent coating delays this process, giving the people inside the building and the emergency services more time to safely evacuate. The paint swells up to 50 times its original thickness to form a carbon layer, or char, that prevents oxygen from reaching the substrate for a given period. In the case of a steelwork roof, for example, the char prevents the metal from bending too quickly, and therefore delays its collapse. Fire-resistant paint products commonly provide 30, 60, 90 or 120+ minutes of protection.

Fire-resistant paint and health and safety compliance

A newly constructed building must have adequate fire protection to comply with the Building Regulations 2010. Intumescent paint is cost-effective, easy to apply and readily available, making it the most widely used method of fire protection for steel structures.

What are the dangers of not applying fire-resistant paint to structural steelwork?


Unprotected steelwork can lose its load-bearing capacity and become structurally unsafe within minutes when exposed to extreme heat. The image below demonstrates how an underground car park becomes structurally unsound without adequate heat protection in the event of a fire.

heat resistant paint on steekl

(When the Paint Coating fails on a steel substrate in an underground car park.)

How to correctly apply intumescent paints to steelwork

Fire-resistant paints only provide their stated level of time protection and meet building regs when applied correctly. The steps below describe the coating system for applying intumescent paint to steelwork.

1. Preparation

Prepare and blast clean the steelwork in accordance with the requirements of any industry-specific standards. Ensure that the surfaces to be coated are free of contaminants such as grease, oil, rust and dirt.

2. Prime the steel

Use a suitable anti-corrosive primer to protect the substrate and to provide the intumescent coating with a good surface for adhesion.

3. Apply the fire-resistant coating

Choose a fire-resistant paint that meets your fire protection requirements. Follow the manufacturer's preparation, drying times and wet film thickness requirements on the product datasheet to prevent the film from failing.

Application method

Most intumescent coatings can be applied by spray, brush or roller. For speed and quality of finish, use a spray gun.

How to meet application wet film thickness requirements

How to Use a Dry Film Thickness Gauge

How to Use a Wet Film Thickness Gauge

4. Apply the topcoat

If required (see below), choose a suitable topcoat that protects the fire-resistant coating and substrate from environmental and use conditions. Follow the manufacturer's preparation and application information on the product datasheet.

Application method

Most topcoat products can be applied by spray, brush or roller. For speed and quality of finish, use a spray gun.


When does fire-resistant paint require a topcoat?

Standard interior application

Unless desired for aesthetics, it is not necessary to add a protective topcoat as the fire-resistant coating will not be exposed to environmental conditions that might cause it to degrade prematurely.

Exterior semi-exposes and high ambient humidity application


In these environments, a topcoat is necessary to protect the intumescent paint from being exposed to conditions that may affect its durability and performance.


Which is the best brand of intumescent paint for your application?

Your choice of fire-resistant paint will depend on the type of project that you're working on. Our customers report having superb results with Jotun and Ultrimax products.


Jotun is a well-known and trusted brand. The Norwegian-borncompany has an excellent track record for producing high-performance coatings that meet heavy industry marine specifications.

Jotun Steelmaster 600WF - White - Intumescent Paint


jotun steelmaster 600WF

Jotun Steelmaster 600WF Intumescent Paint is a one component waterborne acrylic thin film heat resistant coating.

  • Independently approved for fire protection of structural steel exposed to cellulosic fire.
  • Can be used as mid coat or finish coat in atmospheric environments. Suitable on approved primers on carbon steel substrates


Jotun Steelmaster 60SB - White - Intumescent Paint

jotun steelmaster 600WF

Jotun Steelmaster Intumescent Paint

Steelmaster 60SB is a high-solids (solvent-borne) single-pack, thin-film intumescent coating. It is designed to be used as the reactive mid-coat in a full passive 90-minute fire protection system for steel constructions.

Suitable for:

  • Structural steel exposed to external environments up to corrosivity category C4 (ISO 12944-2), with a compatible topcoat
  • Mid-coat or finish coat in atmospheric environments


Utrimax Heat Resistant

Ultrimax has been manufacturing industrial paints since 2006. The company has gained a reputation for Jotun-style quality, easy-to-use online ordering and direct customer service from their Yorkshire HQ.

Ultrizinc Heat Resistant Paint


Need more advice on intumescent paints or heat resistant?

Give our friendly Total Paint Shop Support Team a call on 01302 856666 or drop us an email at sales@ultrimaxcoatings.co.uk.

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