When structural steel is exposed to fire, every second matters. Steel does not burn, but its strength and load-bearing capacity can decrease significantly as temperatures rise. This is why passive fire protection is essential in buildings and industrial facilities where structural steel must remain stable during a fire.

One technology designed to address this challenge is intumescent fire protection.

CharCoat SC is a water-based, thin-film intumescent coating designed to protect structural steel for up to 120 minutes, tested to BS 476 Part 21.

But how does a coating only a few hundred microns thick transform into a protective insulating layer during a fire?

Let’s look at the process step by step.

What Is Intumescent Fire Protection?

Intumescent coatings are passive fire protection systems that react when exposed to fire.

Unlike conventional protective layers that simply act as a physical barrier, an intumescent coating changes its physical structure when heated.

With CharCoat SC, exposure to fire triggers a controlled chemical reaction. The coating expands approximately 20–30 times its original thickness, creating a durable insulating char layer.

This expanded char slows the transfer of heat from the fire to the underlying steel, helping maintain the steel’s structural stability during fire exposure.

How CharCoat SC Works: 4 Stages

1. The Steel Starts With a Thin Protective Coating

Under normal conditions, CharCoat SC forms a thin, smooth coating over the structural steel surface.

The product is designed as a single-component, water-based system, allowing application by brush or spray. CharCoat’s technical information lists dry film thicknesses as low as 250 microns, depending on the application requirements.

At this stage, the coating has a relatively low profile and can provide a smooth architectural finish.

This makes thin-film intumescent coatings particularly useful where maintaining the appearance of exposed structural steel is important.

2. Fire Exposure Activates the Intumescent Reaction

When a fire develops around the protected steel, heat begins transferring through the coating.

This triggers the intumescent reaction within CharCoat SC.

Rather than remaining as a thin film, the coating begins to expand rapidly.

This is the critical transition from a thin protective coating into a much thicker thermal barrier.

3. The Coating Expands and Forms Char

As the reaction progresses, CharCoat SC expands approximately 20–30 times its original thickness.

The expanded material forms a robust, insulating char layer over the steel.

Think of it as the coating building its own protective barrier precisely when the steel needs it most.

The resulting char is significantly thicker than the original coating and acts as insulation against the extreme temperatures generated by the fire.

4. The Char Slows Heat Transfer to the Steel

The purpose of the expanded char is not to extinguish the fire.

Its role is to slow the rate at which heat reaches the steel.

By creating an insulating layer between the fire and the steel substrate, CharCoat SC helps delay the rise in steel temperature.

This additional protection can help maintain the structural stability of steelwork for the required fire-resistance period.

CharCoat SC is engineered to provide up to 120 minutes of fire resistance for structural steel, with the product page identifying BS 476 Part 21 as the applicable fire-resistance standard.

Why Does Intumescent Expansion Matter?

The key advantage of intumescent technology is the difference between the coating’s normal thickness and its fire-exposed thickness.

Under normal conditions:

Thin coating → Minimal visual impact

During fire exposure:

Heat → Intumescent reaction → 20–30× expansion → Protective char → Reduced heat transfer

This allows a relatively thin coating system to provide a much thicker insulating barrier when it is actually needed.

Why Use a Thin-Film System for Structural Steel?

Traditional fireproofing systems can add significant thickness and weight to structural elements.

CharCoat SC is designed as a thin-film system, with exceptionally low dry film thicknesses and a smooth finish. The product information also identifies it as a water-based, zero-VOC formulation.

This can make it suitable for applications where both fire performance and appearance matter.

CharCoat SC is listed for applications including:

• Commercial buildings
• Residential buildings
• Industrial plants
• Power stations
• Mining and smelting facilities
• Steel plants
• Warehousing and industrial units
• Airports
• Stadiums and leisure facilities
• Shipyards

CharCoat SC: Protection Without Heavy Fireproofing

Structural steel fire protection doesn’t always need to mean bulky protective systems.

CharCoat SC combines:

• Water-based intumescent technology
• 20–30× expansion
• Up to 120 minutes fire resistance
• BS 476 Part 21 testing
• Low dry film thickness
• Single-component application
• Brush or spray application
• Zero VOC formulation
• Smooth architectural finish

The result is a fire protection approach designed to integrate with the structure rather than visually dominate it.

The Science Behind the Protection

The most important point to understand about intumescent fire protection is that the coating is designed to change when exposed to fire.

It starts as a thin protective film.

Heat activates the system.

The coating expands.

The expanded material forms char.

The char acts as insulation.

That insulation slows heat transfer to the steel.

And by slowing the rate of temperature rise, the system helps extend the period during which the protected steel can maintain structural stability.

This is the fundamental principle behind CharCoat SC’s intumescent technology.

Protecting Structural Steel Before Fire Happens

Passive fire protection works differently from active fire protection systems.

It does not require someone to activate it when a fire occurs.

The protection is already present on the steel, waiting to respond when exposed to heat.

That makes correct specification, application, dry film thickness, inspection, and system selection critical parts of a structural fire protection strategy.

For projects where structural steel requires thin-film intumescent protection, CharCoat SC provides a water-based solution engineered for interior and semi-exterior applications.

CharCoat SC doesn’t simply sit on the steel—it reacts when the steel needs protection.

A thin coating becomes an expanded insulating char when exposed to fire, creating a thermal barrier that helps delay heat transfer and protect structural steel.

With up to 120 minutes of fire resistance, 20–30× intumescent expansion, and BS 476 Part 21 testing, CharCoat SC is designed to provide thin-film passive fire protection without compromising the appearance of the protected structure.

When fire strikes, the coating changes. The objective remains the same: help keep the steel protected.

Learn More

Explore CharCoat SC — Structural Steel Fire Protection

FAQ Section

What is CharCoat SC?

CharCoat SC is a water-based, thin-film intumescent coating designed to provide passive fire protection for structural steel.

How does CharCoat SC protect structural steel?

When exposed to fire, CharCoat SC reacts and expands to form an insulating char layer. This char helps slow heat transfer to the underlying steel.

How much does CharCoat SC expand?

CharCoat SC can expand approximately 20–30 times its original thickness when exposed to fire.

How long can CharCoat SC protect structural steel?

CharCoat SC is designed to provide up to 120 minutes of fire resistance, with fire-resistance performance identified against BS 476 Part 21.

Is CharCoat SC a thick or thin-film coating?

CharCoat SC is a thin-film intumescent coating, designed to provide fire protection without the bulk associated with some traditional fireproofing systems.

How is CharCoat SC applied?

CharCoat SC can be applied by brush or spray, depending on project requirements and application conditions.

Is CharCoat SC suitable for commercial buildings?

Yes. CharCoat SC is listed for applications including commercial and residential buildings, industrial plants, power facilities, mining and smelting facilities, steel plants, airports and other facilities.

What happens to CharCoat SC during a fire?

The coating undergoes an intumescent reaction, expanding and forming a protective char layer that acts as a thermal barrier between the fire and the steel.

Does CharCoat SC replace active fire protection?

No. CharCoat SC is a passive fire protection system. It is designed to complement an overall fire protection strategy rather than replace active fire protection systems.

Why is dry film thickness important?

The required coating thickness is an important part of achieving the specified fire-resistance performance. The appropriate thickness should be determined according to the project requirements and applicable fire-test/system specifications.