After you have stripped your walls back to plaster rendering, you are ready to apply paint or wallpaper. Paint can be applied directly onto plaster; emulsion paint is the preferred medium because it acts as a sealer and is not soaked in too much. New plaster, however, must be perfectly dry before painting, or patches of discolouration may occur. If oil-based paints are used, the paintwork may blister and peel off. Furthermore, efflorescence – white, crystalline deposits of salt – can appear on newly painted walls as the salts rise to the surface of the plaster as it dries.
Wallpaper also provides a good base surface for painting over, provided it is clean, dry, not torn and has no loose areas. If wallpaper is damaged, then painting over it will just make it worse. Always make a test patch first: a dark patterned wallpaper may require two or more coats of emulsion paint to cover it. You might find that dark patterns show up through your paint several days after painting.
Filling Plaster Cracks
If a wall is in good condition, all the preparation required is to wash it down, scrape off any loose material and make good any cracks or holes with filler. Rake out any loose plaster from cracks and holes with a scraper or filling knife and fill using an interior-grade cellulose filler mixed to a creamy consistency – or, if you prefer, use a ready-prepared filler. Dampen the plaster around and inside the crack with a wet paintbrush and press the filler well in. Leave the filler standing a little proud of the wall; some fillers shrink when they dry and any that dries proud can easily be smoothed flush with abrasive paper.
Small holes are best filled with a dab of filler applied with a clean fingertip. Where a crack or hole is deep, it’s best to fill it by building up in layers, allowing each to dry thoroughly.