Intumescents - Fire Inhibiting Finishes

Intumescents are materials that, when exposed to high heat, undergo an endothermic reaction and swell, creating a char that serves as an insulator and a fire-resistant surface. They can be used in passive fire protection applications – those designed to contain or limit the spread of fire in a building – to insulate framing members or seal penetrations to resist the flow of heat and fire. The thickness of the application will determine the fire rating of the system. Under heat expansion, intumescents can become up to 50 times their applied thickness. Intumescents produce different types of chars, some more preferable to use as interior coatings, exterior coatings, or firestopping. For this reason, selecting the correct intumescent for the application becomes an important decision.

Intumescent coatings are often selected over other spray-applied fire resistant materials (SFRMs) because of their aesthetic qualities. They are available in a variety of colors and the finish is much like a painted surface. They are usually applied in several coats, sometimes including base and top coats, to create a film over wall surfaces, panels, exposed beams, and floors. Coating systems are available in different finishes, and can be clear, tinted, or colored to coordinate with the building’s décor and underlying building materials. Different intumescent products can be applied to nearly all types of building materials, including steel, timber, structural insulated panels (SIPs), cement, oriented strand board (OSB), foam, and others.

Their thickness can be from less than 0.1 to 0.5 inches, depending on the fire rating desired. Other SFRMs, such as cementitious coatings, must usually be a half inch thick or greater and have a rougher finish. Labor on cementitious coatings may also be greater because of the required thickness and potential mesh backing necessary for application. Intumescent caulking and gaskets can be particularly useful in firestopping plastic pipe penetrations, as the intumescent can expand to close the pipe and fully block the penetration.

Intumescent construction products are preferable over standard products which do not have a fire rating. When protecting structural framing, this becomes very important. While wood framing can be a fuel, steel loses 75 percent of its strength in temperatures above 600°C. Steel-framed structures protected from heat are less likely to buckle, shift, and fall during a fire, making the building safer for occupants to escape and for fire rescue workers to enter and combat the fire.

Intumescents can provide security and confidence to homeowners as they will not only help protect the structure in a fire, they will also provide additional time to react to or escape from a house fire. They can also reduce toxic smoke and fumes. Additional benefits from some products can include protection against the growth of black mold and anti-graffiti properties. Some manufacturers have intumescents that are non-toxic, non-carcinogenic, and eco-friendly with low VOCs, which may be another selling point for homeowners looking for greener homes with better indoor air quality.

	Intumescents offer a proactive approach to fire protection wherein a home’s structural elements are more protected during a fire. Since intumescents also prevent materials underlying the structural members from becoming combustible, fire may not spread as easily or as rapidly to other areas of the home. Also, since intumescent coatings help to contain fire and heat, providing additional time to react and/or escape from a house fire.

Initial Cost  

Intumescent coatings for home use can range from about $50 to $100 per gallon, varying with the intended surface, such as over drywall or as a wood coating. To achieve some fire ratings, several coats may have to be used. Costs may be higher for industrial intumescent coatings. Labor costs should not be significantly different than the standard rate for painters.

Intumescent caulk is typically about two to four times the cost of typical all purpose caulk. It costs more than typical fire-stop mortar but requires less labor and is easier to remove and correct.

Operational Cost  

Once applied, intumescent coatings do not need maintenance or re-coating. Homeowners must be aware of intumescent use so they can select appropriate top coat products. Some manufacturers indicate that any alkyd or enamel paint may be used over the intumescent layers once dry, but be sure to consult manufacturer’s instructions specific to the type of intumescent used.

The International Residential Code 2003 and 2006 requires fire-resistance-rated construction to be inspected where required between dwelling units or due to location on property (R109.1.5.1). 

Fire-retardant-treated wood shall have a flame spread index of 25 or less when tested in accordance with ASTM E84 and show no evidence of significant progressive combustion when the test is continued for an additional 20-minute period. Additionally, intumescents and other SFRMs are subject to tests involving ASTM E119, E605, and E736 for use under many model building codes.

Underwriters Laboratories (UL) has an extensive program in place that certifies intumescent coatings and contractors.

None available

Typically, intumescent coatings are sprayed or rolled onto the structural elements of the house after the house is framed. Some must be applied by licensed professionals while others can be applied by the homeowner. The substance typically dries within 24 hours. Coatings typically vary between 0.03 to 0.50 inches in thickness, dependent on composition. Depending on the surface to which the intumescent is being applied and the actual product being applied, some surface preparation or priming may be required. The area where it is being applied should be ventilated and contractors should wear proper protection. As with all SFRMs, it is important to ensure an even application in proper thickness because this is crucial to the fire rating of the framing.

Caulking and gaskets are easier to apply because of their isolated nature. Follow manufacturer’s instructions in all cases.

Warranties can be provided and vary in duration, subject to proper installation. Some manufactures certify dealers and installers and include a fire resistance classification (FRCR) Rating as applicable. 

Intumescents offer passive fire protection that can be an aesthetically pleasing and space conserving alternative to other SFRMs. Additionally, fire ratings can be increased with lesser thickness as compared to other types of SFRMs and firestops. While initial material costs are higher, labor costs can be decreased if preparation and application time are reduced.

Some intumescents are susceptible to environmental influences such as humidity and UV light which can reduce or negate their ability to function as intended. Vulnerable intumescents, such as some common sodium silicates, must be protected by epoxy or rubber coatings to ensure performance. Responsible manufacturers will state on the label that the product requires additional protection. It is important to match the intumescent to its intended environment so that its performance is not compromised.