When your building relies on lumber to provide structure and support, it’s important to choose an intumescent paint for wood that will provide a high level of fire protection.
Here, we’ll go over the differences between intumescent and fire-retardant paints for wood, our recommended choice of paint, and how to apply intumescent paint on wood surfaces.
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When deciding how to fireproof lumber, it’s important to consider the differences between fire-retardant paint and intumescent paints.
Fire-retardant paints are designed to slow a fire’s burn rate, slowing the spread of flames throughout a structure. However, they don’t insulate the substrate, so the wood may still become damaged.
Intumescent paints are fire-resistant, which means they protect their underlying material from contact with flames. When exposed to heat, these paints expand, creating a foamy barrier against the flames. This barrier generates a layer of char that buys time before the substrate will burn.
Another major difference: fire-retardant paints are generally ASTM E-84 certified, but not ASTM E-119 compliant. Intumescent paints typically meet both of these safety standards, making them a more flexible choice for coating both interior surfaces and structurally significant areas.
We recommend FlameOFF’s Fire Barrier Paint for wood surfaces because of its ASTM E119/E84 compliance, eco-friendly formula, and versatile applications.
Here’s a look at its key features:
- ASTM E119 compliant, up to 1-hour fire rating for wood assets or assemblies
- ASTM E84 compliant, meets Class A flame spread standards
- Eco-friendly, LEED-compliant with low VOC
- Applicable to wood, gypsum, metal, and other substrates
- No primer required
Check out FlameOFF and their Fire Barrier Paint to learn more.
In this section, we’ll go over the on-site conditions, protective gear, and techniques you’ll need to apply intumescent paint on wood safely and successfully.
Required humidity and temperature
Intumescent paint requires the right temperature and humidity for secure application.
Intumescent paint should be applied in less than 85% humidity, which can be measured with a hygrometer. You can also apply a small section of paint and time how long it takes to dry. Ideal drying times are between 10-15 minutes.
Intumescent paints should be applied at ambient temperatures of at least 45° Fahrenheit (10° Celsius). There is no temperature ceiling for applying intumescent paint.
However, at higher temperatures, intumescent paints dry and cure faster. In direct sun, the surface may dry faster than the paint underneath, creating an unattractive cracked surface. On the other hand, intumescent paints will thicken and may fail to cure in temperatures below 45°.
Drying and curing times will vary depending on the temperature and humidity, so it’s important to monitor your on-site conditions.
First and foremost, always read the instructions associated with your specific safety gear and personal protective equipment (PPE).
The PPE used when applying intumescent paint on wood covers your whole body:
- Eye protection: A face shield, safety goggles, or other shield protects eyes against paint droplets and particles.
- Hearing protection: Ear plugs or a set of earmuffs protect your inner ear against the potentially loud and continuous noise generated by spray equipment.
- Breathing protection: For short-term paint applications, a face mask with filtration will be enough to filter out paint dust and particles. For day-long applications, opt for an air-fed mask.
- Body protection: A simple pair of overalls or coveralls protects clothing from paint spray.
- Hand protection: Latex or leather gloves protect your hands from contact with the paint. Armlets are also an option to protect forearms.
How to prepare the wood for intumescent painting
Before you can apply your paint, you need to clear your substrate of any old paint or residue. Here are your options for preparing your substrate:
- Chemical paint removal: Apply a paint stripper to areas with pre-existing (especially flaking) paint. Let it rest for 15-30 minutes, then scrape off the old paint and clean the surface with hot water.
- Physical paint removal: If you prefer not to use a chemical option, you can use a paint scraper, hot air gun, coarse paper, or sandblasting to remove old paint.
- Removing other substances: For substrates with grease, wax, or other residue, use a strong cleaner or degreaser to remove them. Take care not to damage any other coatings by carefully following your cleaner/degreaser instructions.
Once the surface has been cleaned, you can apply your primer. Some paints, like FlameOFF’s Fire Barrier paint, don’t require a primer and can be applied directly to the substrate. However, a primer or thin coat of intumescent paint is a good idea if you’re concerned the paint may soak into the wood.
Recommended application tools for intumescent paint on wood
You have your choice of using a paint brush, roller, or an airless paint sprayer to apply intumescent paint. The right tool for the job will depend on the shape and texture of your substrate.
Paint brushes and rollers are the cheapest options. Paint brushes allow you to evenly apply paint to rough or unusually-shaped surfaces. Make sure to use an older brush for your final coat — they’re less likely to shed bristles.
We recommend the following techniques when using a brush:
- Use the largest possible brush
- Paint in a criss-cross pattern
- Keep the brush at a 45° angle to prevent visible brush marks
- Clean your brush every 30 minutes to prevent paint from drying on the bristles
An airless paint sprayer, on the other hand, is much faster, requires fewer painters, and yields a uniform distribution of paint. However, these cost more. We recommend you use a paint sprayer with the following calibrations for intumescent paint:
- Spray gun type: Contractor gun or similar (filters removed to prevent jamming)
- Gallons/minute and pressure: minimum 1 gallon/minute at an operating pressure of 3,000 psi
- Spray tip size: 0.021 inch – 0.025 inch
- Fan size: 4-10 inches, depending on the size of the area
- Hose length: 50 feet (maximum)
- Spray hose: 0.5 inch inside diameter (ID)
Using the correct tip size and pressure will ensure a smooth and consistent coating with minimal overspray to the surrounding area. You can further avoid overspray by covering nearby surfaces.
DFT and WFT
Fire ratings require certain degrees of paint thickness, called Dry Film Thickness (DFT) and Wet Film Thickness (WFT). You’ll need to measure both to ensure you’re meeting ASTM standards.
As the name implies, DFT is measured once your paint has fully cured. This is measured with a dry film thickness gauge. Take your first DFT measurement on your primer, then another on your layer of intumescent paint before you apply a topcoat.
WFT is measured while the paint is still wet. Like DFT, you can check WFT with a wet film thickness gauge. Though less accurate than a gauge, you can also estimate your WFT by taking the DFT of a finished area and plugging it into the following calculation:
(Square footage of area x DFT / Percentage of paint solids by volume)
If you’re using a paint brush, aim for a WFT of 10 Mils per coat. For paint sprayers, aim for 20-45 Mils per coat.
Picking the right fireproof paint is the first step towards bringing your facility up to par. Consider FlameOFF’s Fire Barrier paint to achieve E119 and E84-compliant protection for your next project.