Fire retardant treating creates a chemical barrier that restricts the flame spread along the wood. The proprietary retardants are not just on the surface, but are infused deep into the wood to provide durable, safe and long-lasting protection. As a result, the potential useful applications of wood is extended from single-family homes into multifamily and commercial applications where fire risk is a concern for exiting the structure during a fire emergency.
Click on the video to see how
fire retardant treated wood is made
The treating process utilizes pressure that forces the fire retardant into the wood fiber. While there are a variety of fire retardants used today, the manufacturing process is virtually the same for all.
Preparing the Wood
Fire retardant-treated wood manufacturers start the process by purchasing kiln-dried lumber or plywood from forest product companies. The untreated wood is loaded onto carts, which are moved into a specially made cylinder called a retort. The retort, which can be up to 150 feet in length, is sealed and a vacuum is applied to remove the air.
According to the International Code Council (ICC), FR wood also includes those products where retardants are applied “by other means during the manufacturing process.” This does not include spray-on applications, but does allow for fire retardants to be infused during the manufacturing process so that it is an integral part of the panel or beam.
Infusing Fire Retardants
Next, the fire retardant solution is pumped from storage tanks, completely filling the retort. Pressure is continuously applied within the retort to force the fire retardant into the cells of the wood. Processing time depends on the wood species, the size of the products treated and the fire retardant used, as well as the standard for the intended exposure of the final product.
The fire retardant is drained from the retort and a vacuum is applied to return the excess solution to storage tanks for future use. The carts are moved out of the retort onto a sealed drip pad to reclaim any residual fire retardant on the wood.
Building codes require all FR wood products to be dried to a moisture content or 19 percent or less. Following the treating process, the products may be dried in a kiln or placed in an area with large fans to create air flow for drying the wood.
Representative core samples are taken and analyzed to ensure that quality and durability standards are met. Third-party inspection agencies also take core samples during regular visits to confirm the plant's quality control practices.
The finished FR wood products are typically covered with a top wrap and moved to the plant's storage area for shipping.