The paint has not been keyed to the surface, which may be too smooth (as with old gloss paint) or may be chalky (as with untreated kalsomine). Alternatively, rotting timber may be pushing the paint off or rust may have formed underneath. Occasionally, though rarely, paint flakes just because it is inferior quality. Strip small areas of flaking paint by rubbing with fine abrasive paper, fill with a fine surface filler, apply a primer and repaint. Larger areas must be completely stripped and begun again

A common problem on painted woodwork. Prick a blister, if water emerges, damp is trapped under the paint film or is finding its way in from behind. The warmth of the sun turns moisture into vapour, which pushes the paint up into a blister. Strip the blistered paint with a hot air gun and leave the wood until dry. Prime the surface and then repaint the whole of the repaired area. If there is no sign of water, the wood probably has an open grain and air has been trapped under the paint. Again, the sun's heat expands the air forcing the paint to bubble. Strip the blistered paint, fill the open grain with an epoxy based filler and repaint. Or omit the filler and use a micro porous paint

When a paint surface breaks up like mini crazy paving, incompatible paints have been used. The top layer of paint breaks up because it expands at a different rate from the one under­neath. In most cases you must strip the paint with a chemical stripper or heat and start again. However, you can rub down very small areas (only several centimetres square) with a flexible sanding pad or with wet and dry paper damped with water. When the surface is smooth, fill the stripped area with a fine surface filler,

A topcoat does not have good covering power, so always use undercoat to hide the colour of the surface. Poor coverage is also sometimes the result of using inferior paint (especially emulsion). To rectify the problem, put on another layer of topcoat, but switch to using one coat paint, which has more body and covering power than traditional paint.

Too much paint applied in a thick coat results in runs and tears which are extremely difficult to disguise or lose. If the paint is still wet, brush out runs but do not do this if the paint has started to dry. Instead, wait until it is completely dry and then rub down with very fine abrasive paper until the surface is smooth. Clean the surface with a dusting brush, followed by a damp rag. Apply a new topcoat, taking care not to put it

There are a number of reasons why stains occur on a painted surface. For example, water in emulsion may activate impurities in a wall; areas rubbed with a wire brush or wire wool can develop rust stains; deposits in an unlined flue will come through the paint surface. Prevent stains from showing by applying an aluminium primer-sealer before you start painting. If the problem occurs afterwards, brush a primer sealer over the stain and

Spores settling on paintwork which is damp, possibly because condensation has been form­ing on glass or cold surfaces - often lead to mould and black and brown patches. Treat the affected area with a fungicide as directed by the manufacturer, wash the surface

Gloss paint will sink into the surface and lose its shine if the surface was not primed or if either primer or undercoat was not left to dry completely. The problem is also a sign of poor quality paint. The same thing happens to exterior paintwork in exposed coastal regions where weathering is speeded up. Make sure the surface is dry, then rub it down with damp wet and dry abrasive paper. Brush off the dust, pick up any remaining specks with a clean damp rag, then apply a new topcoat. Loss of gloss can also occur if you paint in very cold

Usually caused by applying a second coat of paint before the first has dried. Solvents in the wet paint underneath attack the second coat when they try to pass through it and make it wrinkle. Strip the paint with a chemical stripper or heat and redecorate, this time allowing each coat to dry before

If a newly painted surface feels rough and has gritty lumps in it, paint has been applied with a dirty brush or has become contaminated by the surrounding areas. Alternatively, there may have been bits of skin in the paint if it was not strained before use and had been left standing for a while. Or it may be that dust has settled on the surface while the paint was still wet. To ensure that the problem does not arise again, always paint with clean brushes and use a paint kettle. Strain old paint through a paint strainer or a clean, dust free, old nylon stocking. Use a paint shield or a piece of card to guard against the risk of picking up dirt. When a gritty surface is dry, rub down with a damp wet and dry abrasive paper until it is smooth, wipe clean, then apply a new coat of paint, making sure the

Knots in wood which have not been sealed before you decorate may ooze resin when the sun warms them and the resin will force its way through the paint film. Strip paint away with the edge of a scraper blade, then with fine abrasive paper to expose the knot. Brush knotting over the area to seal it, leave it

It may be that paint is slow drying because the room is badly ventilated or very cold. Open all the windows and doors to improve the ventilation or put a heater in the room to warm the air, If this does not solve the problem, the paint has been applied to a dirty and probably greasy surface. Strip it off with chemical stripper or heat and start again, taking great care to clean the surface thoroughly.

If you can, remove insects which get stuck to fresh paint while the paint is still wet and touch up the surface with a brush and new paint. If the paint has started to dry, wait until it has set hard and then brush away the insects, they make less of a mess that way.