For solid timber the most widely used process for treating both solid timbers and panel products is vacuum-pressure impregnation. This is carried out by specialist companies in large pressure autoclaves under 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) flame retardant chemicals are normally incorporated as an integral part of their manufacture.
Formulations for surface application are approved by the WPA when they are applied in a factory under controlled conditions to achieve the performance set out in Classification Reports from recognised notified bodies.
On site application of coatings is not approved by WPA.