What is it? WEST SYSTEM® 421 Fire Retardant Additive does what it says on the tin – it retards fire. It is a heavy, non-combustible powder that is added to a fresh mix of epoxy.
Used for? An extra layer of fire protection in areas such as galleys and engine rooms, or anywhere there may be a risk of heat absorption that could lead to combustion, including cabins and saloons. It could also be used to line the coffer dams around skin fittings to prevent hoses being burnt through, or to run on partitions beside hot areas such as exhausts. It is especially useful if the partitions themselves are combustible, such as plywood bulkheads or galley headliners.
Mixing ratio: An easy 1:1 by weight. However, at this ratio the additive will greatly increase the viscosity of the epoxy so the resulting mix will need to be applied with a trowel or squeegee.
“This is a very straightforward additive, so just follow the mixing ratio and be prepared to apply a thick layer of material,” Hamish says.
“It will help to apply a coat of epoxy onto a properly prepared (degreased and abraded) substrate first to achieve better adhesion. When tacky, apply the epoxy/421 Fire Retardant Additive mix over the top. If you want to apply further layers of sound-proofing to the partition use peel ply during the application or wash the cured 421 Fire Retardant Additive down to remove the amine blush before sanding.
“Key the surface to promote good adhesion of the soundproofing, although peel ply does that automatically on removal. That’s it – 421 Fire Retardant Additive will give additional peace of mind in areas of the hull with a higher risk of fire.”
We wanted to enclose the engine wet exhaust that runs along the floor between two bunks, so needed a plywood partition. To fireproof the plywood beneath the soundproofing, we decided to treat it with a coat of 421 Fire Retardant Additive.