What Is Intumescent Paint & How Does It Protect Structural Steel?
(This is part of our Built to Resist: The Passive Fire Protection Series of blog posts.)
Fire protection is a critical part of any building project—and when it comes to safeguarding structural steel, intumescent paint is a powerful passive fire protection (PFP) solution. But what exactly is it, how does it work, and why is it so widely used?
Let’s explore how this seemingly simple coating plays a crucial role in holding buildings together during a fire.
What is Intumescent Painting?
Intumescent paint is a specialist coating applied to structural steelwork to insulate it from high temperatures during a fire. When exposed to intense heat (typically above 200°C), the coating reacts by expanding up to 50 times its original thickness. This forms a charred, foam-like layer that acts as a thermal barrier.
This insulating layer:
Delays the structural failure of steel by maintaining its load-bearing strength
Buys valuable time for occupants to evacuate and for firefighters to respond
Meets strict fire resistance ratings under British Standards (BS 476-20/21) and Eurocodes
Why Intumescent Painting Matters for Fire Safety
Structural steel begins to lose strength rapidly when exposed to high temperatures—potentially collapsing within minutes if unprotected. Intumescent coatings are engineered to:
• Maintain fire resistance ratings from 30 to 120 minutes
• Be applied without increasing the load or footprint of steel members
• Deliver aesthetic flexibility, allowing architects to keep structural steel exposed without bulky cladding
They’re ideal for use in:
• Commercial buildings
• Warehouses and logistics hubs
• Schools and hospitals
• Multi-storey residential developments
Best Practices for Intumescent Painting in Modern Construction
For intumescent painting to be effective, the process must be professionally managed:
Surface Preparation
• Clean and degrease steel
• Prime using compatible anti-corrosive primer
Application
• Can be sprayed, brushed or rolled (spraying is preferred for even thickness)
• Requires precise measurement of dry film thickness (DFT) to meet performance requirements
Curing & Inspection
• Requires appropriate curing conditions (temperature, humidity)
• Must be checked for uniform thickness and integrity
• Periodic inspections recommended post-installation
How to Ensure Compliance with UK Fire Regulations
UK Building Regulations (Approved Document B) require compliance with fire resistance performance standards. Intumescent coatings must:
• Be tested to BS 476 or EN 13381 standards
• Be applied by certified contractors
• Be specified according to load factors and steel section types
Always ensure your intumescent paint application is backed by:
Manufacturer datasheets
Fire certification
Installation sign-offs
Common Mistakes to Avoid in Intumescent Painting
Wrong primer: Always use a compatible primer
Inaccurate DFT measurement: May lead to underperformance
Poor site conditions: Cold or humid environments can affect curing
Mixing incompatible systems: Stick to one manufacturer’s system from primer to topcoat
Future Trends in Intumescent Painting
As regulations tighten and sustainability takes centre stage, the future of intumescent coatings includes:
Low-VOC and water-based formulations
Hybrid fire protection systems (combining boarding and coatings)
Advanced inspection technology for non-destructive DFT measurement
Off-site intumescent spraying for cleaner, faster installations (more on this in next week’s post)
Intumescent paint is more than just a surface treatment—it’s a vital, load-saving, life-saving layer in your fire protection strategy. When applied correctly, it offers discreet, durable protection that keeps structures standing long enough to save lives.
Whether you’re working on a new build or retrofitting an existing site, ensuring your structural steel is properly coated could be the difference between recovery and ruin in the event of a fire.
For more information or a quote on any of our Passive Fire Protection services, call JW Simpkin on 01332 664700, email us at enquiries@jwsimpkinltd.co.uk or visit our website www.jwsimpkinltd.co.uk