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Intumescent Fireproof Coatings

Intumescent coatings are applied as a paint at thicknesses typically from 40 to 250 mils thick (one mil is 1/1000 of an inch).


When exposed to fire they swell and expand to form a meringue like foam that protects the steel from deformation.

The major benefit to intumescents compared to conventional fireproofing systems are:

  • Higher aesthetic appeal/ finish

  • More durable finish

  • Ability to provide fire ratings with less thickness

  • Intumescent fireproofing will cost 5-10 as much as conventional fireproofing.


UL designates Intumescent coatings by usage or exposure in three categories:

1) Interior conditioned space, with controlled temperature and humidity conditions;

2) interior unconditioned space, with variable temperature and humidity; and

3) exterior spaces that are permanently exposed to the elements.


Intumescents offer architects and engineers the ability to take full advantage of their aesthetic license. Many mastic coatings offer strong impact resistance and durability.


Exterior products are permanently exposed to the elements, and must meet a weathering program for Intumescent materials. In order to list with UL, they have to withstand rain, wind, humidity, UV-exposure, and other elements. The thickness of a coating for structural steel depends on the size of the steel member, the fire-protection rating required for the steel or assembly, and the protection the coating itself provides.

Designers should note that they can significantly cut the costs of Intumescent fireproofing by incorporating larger steel members at time of structural design.   Contact us at Penta Protective Coatings to talk to an expert.

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