Intumescent coating process

Intumescent coatings are a powerful tool in passive fire protection that expands and chars when exposed to high heat and flames. With its proven fireproofing abilities as well as its seamless aesthetic appeal, intumescent coating continues to lead the market. Engineers, designers and architects alike trust intumescent coatings to help safeguard lives and protect properties from structural collapse in the event of a fire.

Application Process : How Is Intumescent Coating Applied?

Intumescent coating is typically applied with spray equipment, which allows for a quick application process and a high-quality finish. Other applications, like brushes and rollers, are also common.

Additionally, intumescent coatings require multiple layers to achieve the desired fire protection. The base layer (primer) adheres tightly to the substrate, the intermediate layers contain the intumescent components that swell when exposed to heat, and the final layer (topcoat) provides added protection and durability.

Step 1: Surface Preparation 

The first step is to prepare the surface of the substrate. Any moisture, dirt or other contaminants on the surface can impact the adhesion of the intumescent coating. The surface must be clean and dry, which may require sanding or cleaning the substrate with solvents.

Step 2: Primer 

Most intumescent coating products require the application of an approved primer material applied directly to the prepared substrate surface. Steel generally requires a primer, and a primer is recommended for other substrates to ensure the intumescent coating adheres effectively to the surface and properly covers the area at hand.

Once the primer is applied at the appropriate thickness and cured completely, the intumescent coating layers can be applied.

Step 3: Intumescent Coating

After the primer has dried, the intumescent coating can be applied. The number of layers varies depending on the product specifications, desired thickness and intended fire rating—usually, several coats must be applied to reach the thickness required to adequately protect the structure.

The thickness of each coat can range from 30 mils (0.8 mm) to 500 mils (13 mm), and each layer needs to dry fully before the next layer can be applied.

Step 4: Topcoat 

When the final layer of intumescent coating has cured, a topcoat layer may be needed.

A topcoat can be selected based on requirements. For example, some topcoats provide additional aesthetic appeal, with a smooth, colorful layer that blends in with the surrounding exposed architecture. Alternatively, an epoxy-based topcoat enhances the durability and strength of the intumescent coating, boosting performance and protecting the structure from environmental conditions.

How Does an Intumescent Coating Work?

Intumescent paint is formulated to react to the heat of a fire. When subjected to a certain temperature, typically around 350‒400°F, the intumescent coating undergoes the process of sublimation, which is when the coating rapidly expands up to 100 times its original thickness and results in a stable, carbonaceous char layer. This char functions as insulation, creating a barrier between the flames and the underlying substrate to slow down the transfer of heat.

By delaying heat transfer, the insulating intumescent coating provides critical safety benefits during devastating fire emergencies—where every second counts.

Intumescent Coating Fire Rating 

The ASTM E119: Standard Test Methods for Fire Tests of Building Construction and Materials is designed to evaluate the ability of fireproofing materials to endure fire while maintaining their structural integrity. For example, to become two-hour fire-rated, an intumescent coating must endure fire for two hours before the flames reach the substrate or the structure collapses.

The fire rating of intumescent paint depends on the quality of the product as well as the application process and its resulting thickness. Always check product specifications for more details.