The most widely used process for treating both solid wood components and panel products is vacuum-pressure impregnation. This is carried out by specialist companies in large pressure autoclaves under factory controlled conditions. The treated material is normally then re-dried to a moisture content compatible with end use providing permanent, maintenance-free protection.
For panel products such as particle board and medium density fibreboard (MDF) a WPA approved flame retardant can be incorporated as an integral part of their manufacture.
FR formulations for surface application are approved by the WPA when they are applied in a factory under third-party quality assured processes to achieve the performance set out in fire test Classification Reports for that specific application from recognised notified bodies.
The application of an FR product by brush or spray on the construction site is not approved by the WPA.