How to Apply Intumescent Paint

Intumescent paints are a type of fire-resisting paint that expands up to 50 times its size when exposed to extreme heat. In a fire it is paramount that the structural frame of a building is properly protected to prevent materials from reaching their critical failure temperature. 

Intumescent paint mitigates the potential for a building to collapse due to extreme heat and also helps with slowing down the spread of a fire, providing more time to evacuate buildings safely and potentially save lives.

This type of paint comes in three different types: 

1. Intumescent Paint for Steel
2. Intumescent Paint or Varnish for Timber
3. Previously painted non combustible surfaces (like plaster)

Read our guide to intumescent paint for more information.

Preparation for intumescent paint

Before you get started, it is important to note that there are standards and regulations when it comes to using intumescent paint. In the UK, only EU and BS standards are accepted.

Certification is also required when carrying out a project involving intumescent paint.

Tools you will need

Application methods vary - you can use an airless gun, a brush or roller. 

For speed and quality of finish, intumescent coatings are best applied using airless paint equipment, however, brush and roller application are also possible.

You will need:

• A cloth for cleaning the area
• An airless paint gun (or a paint roller/ paint brush)
• An approved, anti-corrosive primer 
• Intumescent paint that is suitable for the material you are applying to (steel, timber of plaster)
• PPE is necessary for application - you will need masks, safety glasses and protective gloves

Applying intumescent paint

Applying intumescent paint to steel

• Step one

The steel needs to be clean and free from grease, oil, rust, dirt or any other contaminant that may prevent the bonding.

Then coat the steel in an anti-corrosion primer that is suited to the intended environment of the building. It is important to note that Intumescent paint is not compatible with all primers 

These include:

• Chlorinated rubbers
• Bitumen
• Thermoplastic primers

Note: If the steel you are painting has been galvanised or coated with a zinc-rich primer, then a suitable tie-coat should be applied. If steel is left exposed to the atmosphere with just a zinc rich primer, surface salts may build up on the steel. These salts, if not adequately removed, may cause adhesion problems for any subsequent coating applied. 

• Step two

Apply the primer using your painting equipment - the primer should be applied in accordance with the manufacturer’s instructions.

Ensure that this coat adheres to coverage requirements and then leave to dry for around 8 hours before moving onto the next step.

• Step three

Using your painting tools, coat the steel, adhering to coverage requirements outlined on the tin. Wait another 8 hours before applying anything else to the area.

Airless Spraying Application: It may be applied up to a maximum wet film thickness (WFT) of 1.0mm in a single spray coat - consisting of several quick passes. Read the instruction manual for more information.

Brush/Roller Application: For brush application use a “laying on” technique to avoid heavy brush marking. Maximum wet film per coat when applied using a brush or roller is 6.1mm. A short pile roller will produce a light textured finish.

• Step four

Apply a top coat  once you are sure that the first coat is completely dry. The top coat protects the intumescent coating from the harsh effects of the environment. This should be left to dry for 24 hours.

The top coat is extremely important especially if the steel is external or in a high moisture environment then a topcoat is recommended.

Applying intumescent paint to wood

Step one

Before being coated with a compatible primer, the wood needs to be clean and free from dirt or any other contaminant that may prevent the bonding.

Step two

Apply the primer using your painting equipment - ensuring that this coat adheres to coverage requirements. Leave to dry for around 8 hours before moving onto the next step.

Step three

Using your painting tools, coat the wood, adhering to coverage requirements outlined on the tin. 

Step four

Apply a top coat - the top coat protects the intumescent coating from the harsh effects of the environment. This should be left to dry for 24 hours.

The top coat is extremely important especially if the wood you are painting is in a high moisture environment.

Important things to consider

• Never apply intumescent paints in temperatures below 5ºC or above 30ºC. It is vital that care is taken with profiles that are exposed to the sun as they can reach high temperatures that can cause issues with paint.

• Intumescent products do not maintain their properties forever - how long the product remains effective can be influenced by; how the product has been applied, under what conditions and on its finishing or sealant layer.

*Please note, we no longer stock intumescent paint. However, you can explore our website for a wide range of other fire stopping and fire door products.