Last edited 08 Nov 2020

Intumescent coatings in buildings

An intumescent is a substance that, when exposed to heat, increases in volume and decrease in density. Intumescent coatings are commonly used in passive fire protection. They are typically water-based, solvent-based or epoxy-based paint-like materials that expand when heated to form a ‘char’ which protects steel in the event of fire. This is important as steel softens at high temperatures, which can cause structural collapse. Steel can also be protected from fire by being encased in masonry, concrete or plasterboard,

Intumescent coatings can be categorised as either thin film or thick film.

Thin film coating systems tend to be either solvent- or water-based and can be used for fire protection in buildings with resistance requirements of 30, 60 and 90 minutes. They usually consist of three layers:

  • Primer.
  • Basecoat (the reactive component).
  • Sealer coat.

The typical expansion ratio of a thin film is 50:1, meaning that a coating 1 mm thick will expand to approximately 50 mm when in contact with fire. The advantages of thin film are that both solvent and water-based coatings can achieve decorative and bespoke surface finishes, and can easily cover complex shapes.

Thick film coatings systems tend to be epoxy-based and have been modified for use in buildings having originally been developed for offshore and hydrocarbon industry applications where the test heating process is more stringent than that for industrial and commercial applications. The typical expansion ratio is much lower than thin film, usually 5:1.

Standardised fire tests must be carried out to certify intumescent coatings for steel construction. Technical standards such as BSI, ASTM and ISO provide details for individual building parts.

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