What Is Intumescent Paint And When Should You Apply It To Your Steel?

Intumescent refers to a substance that swells as a result to being exposed to heat.

When heat is applied to the substance, its density will decrease and it’s volume will increase.

In other words – it gets bigger.

It’s the same for intumescent paint.

When the paint is exposed to heat it will expand and thicken. In fact, it can swell to 50 times the original thickness of the paint.

This is extremely useful in helping to protect steel structures.

As the paint is exposed to the heat, it ‘intumesces’ to form an insulating protective carbon layer around the steel.

This is known as a ‘char’.

Why does steel need protecting against heat?

Of course, steel is an incredibly strong substance that can support huge loads.

But if structural steel is heated to between 550 and 620 degrees, there is a risk it could lose its load-bearing capacity and buckle.

Below these temperatures the steel is said to be ‘elastic’. This means it can bend but will always return to its original shape as loads are added and removed.

But if the steel is heated to between 550 and 620 degrees it becomes ‘plastic’. This means it becomes stiff and is liable to buckle and break.

More worryingly, this could cause a steel structure to collapse completely.

This is a major concern.

In the event of a fire for example, if structural steel is unprotected, it can take just minutes for it to heat up to 550 degrees.

But this is where intumescent paint can be extremely valuable.

Coating steel with layers of intumescent paint can add 30, 60 or even 90 minutes extra protection from the heat.

It’s valuable time that could help prevent a potential disaster.

As mentioned before, exposure to heat causes the intumescent paint to expand and form a protective ‘char’ layer around the steel.

It can be extremely effective and it’s no wonder intumescent paint is one of the most common forms of protection for structural steel.

When should you apply intumescent paint?

Intumescent paint can be applied at any time, before or after construction.

However, there are pros and cons in each case.

The key challenge when applying intumescent paint is that until it’s properly dry it can be particularly sensitive and if handled too often it can begin to crack.

This is why we’ll often apply the various layers offsite, so when it arrives for construction it is in good condition.

That said, as there is a risk the coated steel could suffer from scuffs and damage during construction, it is often best practice to apply a finishing coat onsite if required.

Of course, where intumescent paint is required to protect the integrity of a steel structure, here at Fussey Engineering we always assess the situation thoroughly and advise the best approach for the project.

We understand that properly applied intumescent paint could be the difference between a small set back and a major disaster, which is why we take it very seriously.

So, if you’d like to find out more about intumescent paint and how it can be used to protect new or existing steel structures, don’t hesitate to get in touch with us to discuss it further.

You can call us on 01469 540644 or email us at info@fusseyengineering.com for more information.