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Do’s and Don’ts for Maintaining Fire Protection and Compliance
Intumescent coatings play a critical role in passive fire protection—particularly in buildings where structural steel or timber elements are exposed. These coatings are designed to expand when exposed to high temperatures, forming an insulating char that helps delay structural failure during a fire.
But what happens when those protected surfaces need a fresh coat of paint for aesthetic reasons? Can you paint over intumescent coatings without compromising their fire performance?
In this article, we explore when and how you can paint over intumescent coatings, the risks involved, and how to maintain compliance with UK fire safety standards.
What Is Intumescent Coating?
Intumescent coatings are specially formulated paints that react to heat by swelling up to many times their original thickness, forming a dense, charred layer that insulates the underlying material from high temperatures.
These coatings are commonly used to protect:
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Structural steelwork in commercial or public buildings
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Timber in residential and heritage properties
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Service penetrations or linings in compartment walls and ceilings
Their use is typically required to achieve specific fire resistance ratings (e.g. 30, 60, 90, or 120 minutes) as outlined in Approved Document B of the Building Regulations.
Can You Apply Paint Over Intumescent Coating?
Yes— but with important limitations.
You can apply a top coat over an intumescent base coat, provided that the product is approved for use with intumescent systems and does not affect the fire performance.
Many intumescent coating systems are designed to be part of a three-layer system:
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Primer – Ensures adhesion to the substrate (e.g. steel or timber)
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Intumescent basecoat – The fire-protective layer
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Top coat (optional) – For decorative or durability purposes
Top coats must be compatible with the intumescent system and should only be applied if specified by the manufacturer.
The Do’s and Don’ts of Painting Over Intumescent Coatings
DO:
Check the manufacturer’s technical data sheet.
Each intumescent coating has specific application requirements. Some systems require a compatible top coat for durability, while others must remain exposed.
Use approved top coat systems only.
Manufacturers will usually provide a list of compatible decorative finishes. These are tested to ensure they don’t inhibit the performance of the intumescent layer during a fire.
Apply in the correct film thickness.
Top coats are typically limited to a specific maximum dry film thickness. Exceeding this can impact the expansion properties of the intumescent layer.
Maintain access to inspection records.
If you’re repainting, ensure any certification or application records are retained and updated. Fire inspectors may request proof that coatings were applied and maintained in accordance with the system’s requirements.
Consult a specialist if in doubt.
For commercial or regulated buildings, it’s best to speak with a fire protection contractor or coating specialist before making any changes.
DON’T:
Do not use generic household paints or varnishes.
These may prevent the intumescent coating from expanding as intended, potentially rendering the system non-compliant.
Do not sand or abrade the existing intumescent layer.
Damaging the surface could compromise the fire-resisting properties and require reapplication or repair by a qualified contractor.
Do not assume all water-based or breathable paints are safe.
Even breathable or thin decorative finishes can alter how intumescent coatings behave under fire conditions if they haven’t been tested together.
Do not conceal coated surfaces behind false ceilings or cladding.
Doing so can interfere with the performance and inspection of passive fire protection systems.
Maintaining Compliance in the UK
If your building relies on intumescent coatings to achieve a fire resistance rating under Building Regulations (Approved Document B) or a fire risk assessment, you must ensure that any painting or decorating does not alter their function.
In regulated environments such as:
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Commercial buildings
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Residential apartment blocks
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Schools, hospitals, or care homes
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Heritage buildings with protected timber structures
Even minor decorative works should be carried out in line with fire safety requirements.
Failure to comply may not only invalidate your fire protection measures but could also result in:
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Failed building control sign-off
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Breaches of the Regulatory Reform (Fire Safety) Order 2005
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Enforcement action or increased liability in the event of a fire
Final Thoughts
While it is possible to paint over intumescent coatings, it must be done with care, using manufacturer-approved products and techniques. Whether you’re refreshing steel beams in a commercial unit or redecorating exposed timber in a converted barn, the fire performance of your passive protection must always come first.
If you’re planning renovation or redecoration works involving intumescent-coated surfaces, speak to the experts first.
At Martyn Young Fireproofing Consultancy, we offer expert advice on a range of intumescent products. Contact us today on 07585 896648