Hardboard-Masonite/Pressed Wood. Made from chipped wood and reconstituted with resin (adhesive) under pressure. Available in interior and exterior grades with or without factory primer applied. Used extensively on exterior applications painted with a factory applied primer coat. ( Factory applied primers are intended for short term protection of the material while in transit and prior installation. They should not be considered a full prime coat prior to the application of field applied finishes.) Production materials and fabricating methods vary according to manufacturer and geographical locations of plant. Most West Coasts raw materials are composed of redwood and cedar (back of board dark brown) where Southern and Eastern varieties utilize yellow pine (light to medium gray). Each manufacture offers their own painting specifications, but the following will provide acceptable recommendations.
1. NOT FACTORY PRIMED. This is seldom encountered for exterior work. Requires prompt protection with a full coat of oil/alkyd primer or a full coat of stain blocking latex primer. Finish with two coats of latex or oil type finish coat. On interior use, hardboard should be treated as unfinished wood. Some coarse “chipboards” require a filler coat if a completely smooth surface is desired.
2. FACTORY PRIMED. Effective way of protecting the face and lap board siding during transit and during installation. All hardboard manufactures stress that pre-primed hard board must be finished before 90-120 day after exterior exposure. If finishing is delayed beyond that period, treat the exterior siding as though it were unprimed (i.e. requires an exterior primer and two finish coats). Failure to follow these precautions can cause premature delaminating (peeling) of the finish coat from the primer. Directions for application of siding (as listed on packages) should be followed, paying particular attention to vapor barrier instructions. Hardboard should be protected from the weather, as any water may cause stains that reappear after finish has been applied.