If the surface is very porous, apply an alkai-resistant primer or block filler. Cover with latex house paint. To prevent recurrence of efflorscence on interior walls, the exterior walls should be sealed. It is fabricated by reducing natural wood to fibers, adding resins, and then pressing the fibers together into panels. It can be either tempered or standard.
Tempered board is denser and has a higher moisture resistance.
Standard hardboard should not be used outdoors in areas where it will be directly exposed to the weather. Peeling is often due to poor maitenance of the coated surface. It generally originates with bare hardboard in these areas eventually penetrates into the board to repeatedly permeate and expand the compressed wood fibers in the board. The swelling process is irreversible, resulting in delamination of both the paint film and the board. All joints or bare edges must be primed and caulked to avoid contact with water.