Filling Holes and Cracks Prior to Painting

Filling holes and cracks

Most fillers fall into one of two categories: resilient fillers and non-resilient fillers. Resilient fillers — mastics, for example — are useful for lilting gaps between dissimilar materials where movement is expected. Non-resilient fillers —

t hose based on plaster and cement, for example—are more suitable for filling cracks in materials which do not move much, like concrete and plaster.

General-purpose fillers should be able to expand and contract to cope with substrate movements yet they should set sufficiently hard to give a good surface for painting over.

Cracks in plaster

Most cracks in plaster are due to shrinkage and settlement which takes place soon after a house is built. Once they have been dealt with — an interior general-purpose filler is satisfactory they are unlikely to require filling again.

Remove any loose material and rake out the crack with a triangular paint scraper,: It is not necessary to wet the crack, just pack the filler into it as tightly as possible. If the crack is deep and wide, fill in layers no deeper than 10 to 15mm each time and allow each layer to dry before putting on the next one. Leave the surface of the final layer just proud of the adjacent plasterwork. When the filler has dried hard, rub it down with a fine abrasive paper over a block of wood or cork, leaving the surface of the filler flush with the plasterwork. The filler will absorb more paint than the adjacent plasterwork, so it must be sealed before the entire wall is painted. Use two coats of a universal primer or emulsion paint over the filled and adjacent area.

A badly-cracked ceiling can be difficult to fill satisfactorily — wallpaper or textured paint may be the best solution.

Cracks in plaster on plasterboard

Many interior walls are built by fitting sheets of plasterboard with a thin coat of a suitable finishing plaster over the whole surface.

Plasterboard is also used for ceilings. Cracks can appear in the finishing plaster when individual plasterboard panels move slightly. These cracks are easy to spot — they run in straight lines. But they are very difficult to fill. A general-purpose filler is likely to be too rigid and will soon crack again. A resilient filler such as mastic, could cope with the movement but would produce an unsatisfactory surface finish.

Plasterboard ceilings are often finished with a thick textured paint which is flexible enough to hide cracks beneath it. This is a useful way of dealing with a large area of fine cracks. If you wish to retain a flat finish, work textured paint into all the cracks with your finger and smooth the surface off immediately with a damp sponge.

Cracks between ceilings and walls

These occur frequently in new houses and are mainly due to the house settling and the plaster shrinking.

Almost all general-purpose interior fillers are too rigid to deal with these cracks and a resilient filler is likely to produce an unsatisfactory finish. Textured paint is worth trying but the gaps are often too wide and the paint comes out as it is wiped over.

If the area between the wall and ceiling is severely cracked or if the crack appears again soon after filling, mask the cracks with a fabric-based self-adhesive tape or cover with coving. Lightweight expanded polystyrene or polyurethane coving can be cut with a tenon saw and stuck in position with a polystyrene tile adhesive. Some manufacturers supply matching corner pieces. Always prime coving with emulsion paint, never use an oil-based primer.

Cracks in wood joints

Gaps often occur in window joints where two pieces of wood have their grains perpendicular to each other.

A general-purpose filler should cope successfully with gaps in wood joints indoors. For small gaps, pack the filler in with your finger and smooth the surface off immediately with a damp cloth. If there are hard ridges of old paint around the cracks cut them back with a knife.

28. July 2011 by admin
Categories: Internal Repairs, Painting, Preparation, Walls | Tags: , , | Comments Off on Filling Holes and Cracks Prior to Painting


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