Understanding Intumescent Paint: How It Works and When to Specify It

Structural steel is strong, but it loses strength quickly at high temperatures. Intumescent paint is the most practical way to protect exposed steelwork: it looks like a normal coating, but in a fire it reacts and buys the structure time.

How intumescent coating works

At normal temperatures the coating is a thin, decorative film. When exposed to fire, it expands to many times its original thickness, forming an insulating char layer that slows the temperature rise of the steel underneath. That delay keeps the structure stable long enough for evacuation and firefighting.

What fire ratings mean

Ratings such as 60, 90, 120, 150, or 180 minutes describe how long the protected member stays below its critical temperature in a standard fire test. The rating you need comes from the building code, the building type, and the fire safety design. NBL Intumescent Paint is certified for ratings up to 180 minutes for steel structural surfaces by the Vietnam Fire and Rescue Police Department.

When to specify it

• Exposed steel frames in factories, warehouses, and public buildings
• Projects that need PCCC approval in Vietnam or equivalent approvals abroad
• Structures where cladding or boarding would add weight, thickness, or cost
• Timber and aluminium elements that require certified protection

Choosing the right thickness

Required dry film thickness depends on the fire rating, the member type, and its section factor (Hp/A). Slender members heat up faster and need more coating. Our technical team reviews the structural drawings and calculates the exact thickness for each member group, so the certification holds up on site.

A complete system

Intumescent paint performs as part of a system: an antirust primer such as NBL-P022, the intumescent layer NBL-R137, and a decorative topcoat such as NBL-S169 for exposed or exterior conditions. Specifying the full system protects both the steel and the fire rating itself.