How Intumescent Coatings Work

December 7, 2012

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Fire protective or intumescent coatings are specialized substances that help to protect the components of a building, particularly steel structural components, in the event of a fire. These coatings react chemically to high temperatures, expanding and forming a protective char that doesn’t conduct heat well—which works to keep the substrate from collapsing until the flames can be extinguished.

The components of intumescent coatings

Most intumescent paint is either solvent-based or water-based, and made with either acrylated rubber or epoxy that serves as a resin binder. In order for the chemical reaction to occur, these coatings depend on three active components: polyols (such as starch or pentaerythitol), which supply carbon; ammonium polyphosphate, a source of acid; and an expanding agent called melamine.

What happens when fire protective coatings get hot?

Intumescent coatings begin to react at temperatures of around 250 degrees Celsius. The char is formed through a four-step process:

  • The rubber or epoxy binder begins to soften in response to the heat
  • Organic acid is released into the mixture by the ammonia polyphosphate
  • The polyols undergo carbonization, making the mixture harden and thicken
  • Decomposition of the melamine produces gas that swells the resultant char, expanding it up to 50 times the original thickness of the coating

In addition, many types of fire protective coatings contain hydrates, sodium silicates, and graphite elements. These components release water vapor in response to heat, which produces a cooling effect that further strengthens the char.

How intumescent coatings protect substrates

One of the most common uses for fire protective paint, particularly in commercial and industrial applications, is for steel structural elements. These integral components of a building’s foundation can mean the difference between a burning facility and a collapsing one.

While steel is a highly durable material, it begins to lose structural integrity at temperatures of around 550 degrees Celsius. The char formed by intumescent coatings shields these components from heat, preventing them from reaching critical temperatures for up to a further four hours. This provides additional time for occupants to escape, and for firefighters to extinguish the flames.


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