What are intumescent coatings?

While intumescent coatings may seem like the "hot" topic in construction, they've been around for nearly three decades. However, like any technology, it has taken a great deal of time and money to perfect the products that are available today. Earlier products and even some that are currently available can be thick, lumpy and difficult to apply. Some do not bond well to various substrates. Others are toxic and carcinogenic. Still others require special primers and, if you choose, special topcoats.

How do intumescent coatings work? A chemical reaction takes place in the coating when it is exposed to flame or extremely high heat. The coating layer expands and produces a char, which insulates the surface (helping to keep it cooler) and helps keep oxygen — necessary for combustion — away from the substrate.

Exterior intumescent coatings are typically epoxy-based, Williams says, offering good corrosion resistance and less weight than cementitious coatings. Epoxy intumescents are used in the petrochemical industry for exterior applications on refineries and offshore platforms. Because they are known for their impact strength, adhesion and resistance to humidity, they are also being looked at for some interior applications, such as swimming pools, clean rooms and high-rise structures, Williams adds.

The earliest developed intumescent coatings were sensitive to moisture over time and required re-application.  New intumescents have overcome this limitation, and can last for several years.  However, as with any coatings, periodic touch-up and recoating are necessary.

The final appearance of intumescent coatings is similar to standard paint finishes.  The resulting finish is two to four times as thick.  They are available in pigmented and clear finishes.  Recoating may be required after 3 to 5 years depending on the substrate and interior environment.

In commercial construction, intumescent coatings are commonly discussed when a solution more unique than standard fire-rated floor or wall assemblies is required to maintain fire-rating continuity.  Intumescent paints and mastics are coating technologies that utilize char formation to prevent fire spread.  Intumescent coatings can swell up to 100 times their initial thickness upon exposure to fire heat.  These coatings are activated between 300°F and 400°F.  Intumescent coatings often allow architects to expose building structure when fire protection of the structure is required by building code.

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