General:

Many types of composition boards, such as woodpulp (fibre) board, gypsum board, acoustic board, asbestos cement board, woodchip board, etc., are used in building constructions.

Fibre building boards tend to warp or buckle if used in humid conditions and under these circumstances it is advisable to paint the backs and edges before fixing. The fibres of some soft fibre boards may be raised if water paints are applied to them and where appearance is important, care must be taken that the paint does not fill the texture as this will impair the acoustic properties. Flat paint, using the minimum number of coats, gives the best results.

Although the harder grades of fibre boards (such as masonite) have a hard, polished surface, they should not be rubbed down, as abrasion will score the board and spoil its appearance. Some of these hardboards contain water soluble materials which bleed into and discolour waterpaints if not sealed off first with an “oil” paint.

Preparation:

New:
Dust off.

Previously distempered:
It is extremely difficult to remove existing powder distemper from composition boards completely without damaging the face of the board through excessive wetting and scraping. Therefore remove as much of the distemper by careful dry sanding and dust off loose powder.

Previously oil, alkyd, P.V.A. or acrylic painted:
If the existing paint is in poor condition, remove to bare surface by careful scraping and dry sanding, dust off powder. If in good condition, clean down to remove dirt, grease, etc. Sand glossy surface and dust off.