intumescent coating for steel structures on architectural form

Intumescent paint for steel protects and strengthens

Unlike active fire protection like fire extinguishers or sprinkler systems which involve a triggered response to a fire, passive fire protection measures are fire resistance measures. They work by resisting the ignition and spread of fire, insulating against flames and preserving the structural integrity of a building. Fire doors, boards, and intumescent paint for steel are all examples of structural passive fire protection.

Steel is the backbone of the construction industry. It may not burn, but the extreme heat of a blaze will damage steel and weaken its structure, leading to building collapse. Intumescent paint for steel acts to protect steel from the heat of fire by providing an insulating layer between the steel substrate and the flames. By protecting steelwork with intumescent paint for steel you can provide up to 120 minutes of fire protection can mean the difference between a near miss and destruction.

In this article we look and the types and standards of intumescent paint for steel, thick and thin film application, and the products and contractors in the UK.


How intumescent coating for steel insulates structural steel

Steel begins to lose strength at about 300ºC, and this increases rapidly after 400ºC. Given that the average house fire burns at about 600ºC and industrial fires are much hotter, the true danger lies in the threat of structural collapse. When protected by intumescent paint, steel is insulated against the brunt of the heat due to the chemical change it experiences at 200/250ºC. When it reaches this temperature intumescent paint will undergo a reaction and swell to up to 50 times its original thickness, forming a solid foam-like char.

This char insulates the steel substrate beneath from the heat. It is extremely slow burning and resistant to heat and keeps the steel from reaching damaging temperatures, allowing vital extra time for fire crews to get the fire under control or evacuate the building. Depending on the system used, intumescent paint can add an extra 30, 60, 90, or 120 minutes of fire protection for steelwork. Because of this, intumescent coating is quickly becoming one of the most relied-upon coatings for fire protection of steel.

Intumescent paint for steel systems: structural steel, steel beams, steelwork

Fireproof paint for steel beams or structural steel is available in a variety of formulations and can be applied as part of a coating system. There are a range of what are known as ‘fireproof paints‘, including intumescent and fire retardant coatings. The two can be combined to provide an even higher degree of fire protection. Intumescent paint for steelwork is a versatile and flexible solution that can be applied on or off site, commonly as a system including a primer, intumescent basecoat, and a sealing topcoat. Options include:

On site application of intumescent paint for steel

On site application of intumescent paint for steel

  • Water-based intumescent coating
    Water-based fireproof coatings have the advantage of the environmental benefits of being solvent-free, but it also makes them ideal for interior applications where VOCs and odours can be detrimental.
  • Solvent-based intumescent coating
    Solvent-based options are more hardy than the water-based varieties, and so they are the recommended exterior intumescent coating. For exposed or semi-exposed environments.
  • Thin film intumescent coating
    Can be applied on or off site and provide 30, 60, 90, and 120 minutes of protection. Can be applied by brush, roller, or airless spray. The expansion ratio for thin film intumescent steel paint is 50:1, or 50 times its dry film thickness. One of the advantages of thin film coatings is aesthetic – they more easily and attractively cover decorative steelwork.
  • Thick film/high build intumescent coating
    Usually epoxy-based, these coatings have a far higher dry film thickness than the thin film alternatives as they were initially developed for offshore applications and resisting hydrocarbon fires. The expansion ratio is lower than the thin film coatings, usually about 5:1. They can also be applied off site, and are commonly sued for exterior steel structures.

The types and standards of intumescent paint for steel

Legislation regarding fire resistance requirements differs between England, Wales, Northern Ireland and Scotland because the Building Regulations differ by country. In any case, the Building Regulations do not specify the means of fire resistance, only the requirement that a building in designed and constructed in such a way that its stability will be maintained for a reasonable period in the case of fire. As for how to comply with the Building Regulations, there is Approved Document B. This guidance document contains the details of the structural fire resistance requirements for structural stability.

The BSI also has a best practice framework for fire safety as laid out in BS 9999. BS 9999 outlines the fire resistance requirements as a tiered system based on the requirements of the building as outlined in a Risk Profile. Below is a table comparing the required periods of fire resistance for common structures for Approved Document B and BS 9999.

Structure TypeApproved Document B (with sprinkler)Approved Document B (without sprinkler)BS 9999 (with sprinkler)BS 9999 (without sprinkler)
Block of flats with height of more than 30m above access level120Not permitted120Not permitted
Office block with height of not more than 10m above access level60603060
Shops and commercial building with height of 18-30m above access level60906090
Open sided car park with height not more than 18m above access level1515

The minimum periods of fire resistance, in minutes, based on Approved Document B and BS 9999

Intumescent coatings for steel contractors and products in the UK

There is a wide range of intumescent coatings for steel available, and the following is an overview of products with prices including VAT.  A full range of top sealers, both water- and solvent-based, are also available to complement intumescent steel paint.

If you are looking for fireproof paint for steel contractors or products, get in touch! Our experts are here to help you find the right applicators and products for your project. Simply use the “Request a Quote” button beneath this article, tell us the requirements of your project, and let us connect you with the team or solution for the job. 

BrandProduct Type Price
ThermoguardThermoguard Thermocoat W: Waterborne intumescent paint system providing fire resistance to structural steel and cast iron for up to 90mins.£86.40 (5Kg)
BollomBollom Fireshield Ultra Universal: A single pack solvent-based intumescent coating for fire protection of both internal and external structural steelwork.£368.66 (10L)
ZeroflameZeroflame Aquasteel WB+: Easy to apply, quick drying intumescent paint for standard steel sizes and profiles. Available for 30 and 60 min fire prevention.£174.20 (10L)
Sherwin-WilliamsSherwin-Williams Firetex FX5060: a water-based thin film fire paint for steel for 60 minutes fire resistance on structural steel.£212.77 (20L)

Alternatives for intumescent coating for steel

  • Boards are common in the UK. They provide a box-like fire protection around simple and more complex steel structures. Their benefits include being factory made with a guaranteed thickness, and a dry application.
  • Sprays are not so common in the UK even though they have some benefits such as low costs and ability to fireproof complex structures.
  • Flexible blanket systems are used where dry application is needed with complex structures. They are capable of being bent into shape.

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