The main causes of paint breaking down in the most residential and commercial painting jobs are incompatible paints being applied on top of one another, poor preparation of the surface, damp or trapped moisture, grease, rot or rust.
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
- Strip small areas by rubbing gently with fine abrasive paper, fill with a fine surface filler, apply a primer and repaint.
- larger areas must be completely stripped and prepared again from scratch.
Prick a blister – if water emerges, damp is trapped under the paint or is finding its way in from behind.
- Strip the blistered paint with a hol-air gun and leave until it has dried.
- Prime the surface and then repaint the whole of the repaired area.
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.
- Usually, you must strip the paint with chemicals or a hot-air gun and start again.
- Rub down very small areas – no more than a few centimetres square – with a flexible sanding pad or with wet-and-dry paper dampened with water.
- When the surface is smooth, fill the stripped area with a fine surface filler, prime and repaint.
Some strong colours are difficult to paint over effectively.
- A tinted undercoat can help, depending on what colour (or white) is to be the new topcoat. Apply two or three topcoats.
Too much paint applied in a thick coat results in runs that are hard to disguise
- If the paint is still wet, brush out runs; but not 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 with a damp rag.
- Apply a new thin topcoat
Stains occur when water in acrylic paint activates impurities in a wall; areas rubbed with a wire brush or wire wool develop rust stains; or deposits in an unlined flue gradually work their way through the paint surface.
- Prevent stains by treating them with a bleed sealer before you start painting.
- If the problem, occurs afterwards, brush a primer-sealer over stain and then repaint.
MOULD AND DISCOLOURATION
Spores settling on paintwork that is damp – possibly due to condensation forming on it-often lead to mould patches.
- Treat the affected area with a fungicide as directed by the FLAWS AND SPILLS manufacturer, wash the surface clean, let it dry and then repaint.
LOSS OF GLOSS SHEEN
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.
- Rub down with damp wet-and-dry abrasive paper.
- Brush off the dust and wipe with a clean, damp rag, then apply a new topcoat.
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 applying the next.
GRITTY PAINT SURFACE
If a newly painted surface feels rough and gritty, paint has been applied with a dirty brush or has become contaminated by the surrounding areas. Or there may have been bits of skin in the paint. Always paint with clean brushes and use a paint pot. Strain old paint through a paint strainer or old stockings. Use a shield of piece of card to guard against picking up dirt from a floor.
- 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.
PAINT WILL NOT DRY
The room is badly ventilated or very cold.
- Open all the windows and doors or put a heater in the room.
- If these efforts do not solve the problem, the paint has been applied to a dirty – and quite probably greasy surface.
- Strip off the paint with chemical stripper or a heat gun and start again, taking great care to clean the surface thoroughly.
FLAWS AND SPILLS
Act fast if you spill paint. Scrape up as much as you can with a flat-bladed tool. Then dab off what’s left with dry absorbent cloths and paper before lifting the last traces with clean cloths dampened with cold water (for spilt acrylic) or mineral turpentine (for solvent-based paint). Use washing-up liquid on a damp cloth to remove traces of mineral turpentine from fabric.
Paint on glass
The best tool for removing paint from a window pane is a plastic scraper fitted with a trimming knife blade. The blade should be inset very slightly so it cannot mark the frame.
Insects or stray bristles on painted surface
If you can, remove insects or stray bristles that 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 object – they make less of a mess that way.