What is intumescent paint?

what is intumescent paint

If you've never heard of intumescent paint before, then today's post might surprise you as we explore how intumescent paints work as a method of passive fire protection for homes and businesses.

The intumescent coating found in this type of paint has fire resistance properties that can change the world of fire protection mandated by law. It's passive, but it's powerful.

So, if you want to learn more about intumescent paint, how it works, what it is, and how it can benefit us all, then read on for today's post.

How do intumescent paints work?

Intumescent paints are known as reactive paint. When the intumescent coatings are subject to heat exposure over the critical temperature of 120 degrees Celsius, the paint applied will intumesce, which means the intumescent paint expands to swell up to 50 times thicker than the original thickness.

Given that intumescent paint only requires a thin film intumescent coating, the swollen paint won't immediately look massively different, but the secret to its success is in the chemical reaction.

Fire protection explained

When these fire retardant paints are exposed to temperatures above the critical temperature of 120 degrees, the paint forms a carbon layer, which is commonly referred to as char.

Char is a poor conductor of heat, so protects different materials within buildings from getting too hot (which could be incredibly dangerous if the materials that are heating up are structurally important in keeping a building standing).

It is these carbon layers that offer fire resistance for a certain amount of time based on the intumescent paint used.

Fire resistance time varies from 30, 60, 90, or 120 minutes. The longer the intumescent paint can hold out against the fire, the better the fire protection and fire rating of a building.

Chemical reaction explained

Chemical reaction explained

How exactly does this reaction with the chemicals work, though?

Well, the intumescent coating has many different chemicals which react to create the char we've just been discussing.

These chemicals are bound together in a binder to stop them from reacting ordinarily. However, when the heat reaches that magic 120 degree number, the suspended chemicals are released from the binder and react.

That's why these coatings are so impressive, because they will always be ready to work when necessary, but won't accidentally trigger before it's absolutely necessary to do so.

Where are intumescent paints used for passive fire protection?

Intumescent coatings or intumescent paint are best used on load bearing capacity elements of buildings.

This involves many different materials, and an intumescent coating is applied to them to improve their fire ratings.

Here are the 3 most common uses: 

Steel paints

Intumescent paint for steel constructions can be used on structural steel members and cast iron to protect it from fire. When structural steel is protected in this way, it prevents/delays collapse of a building.

In order to meet building regulations then, exposed structural steel and internal structural steelwork should be given an intumescent coating to increase its fire resistance and load bearing capabilities when fire strikes.

Structural steel and cast iron loses its integrity when it reaches temperatures exceeding 550 degrees, which is easy to reach in a large fire.

By using intumescent paint for steel, the intumescent paint system can offer fire protection for around 60 minutes, allowing people the chance to escape before the building collapses.

This is necessary to meet building regulations and building code.

Steel paints

Timber substrate paints

Intumescent paint is also used to increase the fire performance of timber. Again, this is vital when meeting important fire test standards to improve the structural elements of buildings.

The insulating layer can offer timber an additional 30 to 60 minutes of fire protection by reducing the surface spread of the flames thanks to the light char insulating material.

Passive fire protection can work for timber too, despite its natural tendency to burn quickly, by using these thin film intumescent coatings to protect its integrity.

Wood and derivatives of wood are used throughout many buildings. To protect wood and meet high standards in fire resistance, wood must receive an intumescent coating.

Plaster paints

Intumescent paints used for plaster again improve its fire rating and fire performance. Plaster walls and ceilings naturally have a fire resistance time of up to 20 minutes, but intumescent paint can extend this to 60.

Lath and plaster ceilings are common in almost every building, so protecting it with a final layer of intumescent products to protect it from high temperatures and fire is a no-brainer to improve the fire rating of a building.

Plaster paints

How are intumescent products applied to the material used in building construction?

It's interesting to know how exactly these intumescent coatings are applied to the material used in construction to understand how technical the process is.

Where is it applied?

Intumescent paint can be applied to materials in many ways, but it's usually applied off site. That's because the manufacturers of the intumescent product know how much paint is needed to improve the protection of the material against fire.

Sometimes though, the material only requires a simple sealer topcoat which can be applied on site to the steel/timber/plaster, provided the team on site follows the full specification of the manufacturers of the intumescent paint to ensure the correct amount is applied for full protection.

The technical side...

For the intumescent layer to work effectively, something known as the dry film thickness must be absolutely perfect. That's why it's often left to the manufacturers.

Dry film thickness is determined by a number of factors, including:

  • Mass factor - based on how much of the steel is likely to be exposed to the fire, how much load it carries, and the volume of that steel. The higher the risk, the more coating is needed.
  • Exposure - based on how many faces of the steel are exposed. The more there are, the hotter it'll get quicker, and the greater the risk. So more intumescent paint will be applied.
  • Critical temperature - depending on the exact makeup of the material, it may be able to deal with different amounts of heat. The higher the heat temperatures the steel can deal with, the less coating is needed.
  • Duration - how long does this building realistically need to remain protected against fire? The longer it needs, the more coatings are required.
  • Standards - different based on the country. Usually, national tests apply, but any EU regulation replaces national standards, for example. Different coatings will be applied based on where the material is being used based on that country's tests and standards that need to be met for fire protection.

By following these guidelines, intumescent product manufacturers are able to increase the passive fire protection of a building and ultimately improve its fire ratings and save lives. Just by applying the correct thickness of intumescent coatings to guarantee safety.

Intumescent paints in practice

Intumescent paints in practice

Intumescent paint sounds amazing, and it's true that it's a common form of protection against fire in many buildings.

But there are some things that need to be thought about in a practical sense, so we'll cover them below.


Surely, given the almost miraculous working ways of intumescent coatings, the cost must be extortionate?

On the contrary, intumescent coatings and paints are actually a much smarter, cost effective solution to fire protection.

These coatings actually save money in the long run since the damage that is caused by fire, and resulting repair costs, is much less than it would otherwise have been.

Many construction and building businesses see intumescent coating, not as an unnecessary cost, but as an insurance to protect the buildings they've built, and, more importantly, of course, the lives of those living and working in the building.


It's a trivial point considering how we ended the section above, but people will care about the aesthetics of these coatings and paints.

Thankfully, this has been considered too, and the manufacturers that produce intumescent coating provide an aesthetically pleasing finish.

It is usually gloss or satin, but there are some matte finishes too. Whichever is used, though, there is always a smoother finish than a solving based coating.

They come in a range of colours as well, meaning you can always find the look you need whilst thinking about the building's safety too.

Intumescent paint benefits

Before we finish, we're going to share a quick list of the intumescent paint benefits covered throughout today's post, and an additional benefit or two, so you understand why they're so important in construction and fire safety:

  • Protects lots of materials (steel, timber, plaster) and improves their fire resistance
  • Provides anti corrosion protection for steel, specifically
  • Cost effective
  • Delays/prevents building collapse (because the steel won't heat and collapse, the timber and plaster won't burn, and the steel frame of the building can stand long enough for people to escape)
  • Aesthetically pleasing
  • It helps meet standards and tests
  • It won't react until it really needs to
  • The chemicals are always on standby to act when the binder is softened at 120 degrees
  • Additional fire resistance of 30, 60, 90, or 120 minutes, depending on a few different factors
what is intumescent paint


Intumescent paints are an integral part of a building's fire protection, rating, and safety. Only by using this on key materials in buildings (steel, plaster, timber) can you ensure the safety of a building and its occupants when disaster strikes.

Not many people outside of the construction industry will have heard of these intumescent paints, but we hope that by shining a light on them today, more than just those involved in construction can understand what is intumescent paint, how it benefits us all, and how it's used to keep us all safe, no matter what building we're in!

Why Choose


Same Day Service
24hr Call Outs
No Hidden Charges
Lowest Price Guarantee
Over 10 Years Experience
Friendly & reliable


Our uPVC

Spraying Services

UPVC Spray Painting
UPVC Window Spraying
Exterior House Painting
Kitchen Spray Painting
UPVC Door Spraying
Garage Door Spraying
Furniture Spray Painting
Cladding Spraying
Shop Front Spraying
On Site Spraying
Intumescent Painters

Social Media

Copyright © 2023 Revampspray