Pimples
Particularly noticeable in shiny, gloss surfaces, these are caused by specks of dust which may have been on the surface, on the brush or in the paint itself. Or a very fine skin on the surface of the paint (especially non-drip gloss) may have got broken and worked into the paint on application.
Make sure the surface is clean and free of dust at each stage of the work: after burning off or rubbing down, and before applying primer, undercoat and top coat. Clean the surface with a tacky (resin-impregnated) rag or a clean, lint-free one dampened with white spirit. Pay particular attention to corners since pockets of dust here, though difficult to clean with a rag, will be picked up on the brush and spread across the surface. Use a pointed stick under the rag to ensure every particle of dust is removed from the corners. Paint brushes must be cleaned and even new brushes need rinsing before use as the bristles will contain some dust and loose hairs. Wipe the lid and rim of the paint can before removing the lid otherwise any dust will fall into the tin. It is a good idea to transfer a small amount of before paint into a clean paint kettle or other container and work from this. If dust falls into the kettle only a small amount of paint will be affected. Clean the room thoroughly before starting work and allow time for dust to settle using paint.
Don’t try to remove specks while the paint is still wet as you will only add to the problem by smearing the paint. Allow the paint to harden for several days; even though it may seem dry after a few hours, only the surface will have dried. Rub down the affected areas with fine wet and dry glasspaper, wash with clean water, dry thoroughly and apply a new finishing coat. Skin often forms on old paint. If you spot it, carefully lift it away before stirring; if it is extremely thin you can stir it into the paint and then strain the paint through fine muslin or mesh.
Flaking
Paint falling away from surface is due to poor preparation or bad use of primer. It can take weeks to show and will usually be confined to small areas on the surface.
Clean and prepare the surface thoroughly. If stripping back to bare wood apply a suitable primer. Emulsion flaking from walls or ceilings normally means you have applied the paint over distemper. Before painting, remove distemper by washing and scraping off the loose material, covering the remainder with a coat of primer sealer.
If flaking occurs in small patches, strip these areas back to the bare surface, fill depressions with fine surface filler and repaint. If flaking is extensive, however, you will have to strip off the whole lot and start again.
Slow drying
Sometimes paint (particularly oil-based paint) will take a few weeks to dry or even remain permanently tacky. This indicates you applied the paint over a dirty or greasy surface, used an unsuitable thinner or did not stir the paint before applying.
Clean and prepare your surface thoroughly paying particular attention to skirtings which tend to collect a build-up of polish from the floor. Always stir the paint. You can add a small amount of proprietary dryer to stocks of old paint but never to new paint, which should be returned to the manufacturer for testing.
If the room is badly ventilated, open the windows for a few days to see if this accelerates drying. If not you will have to strip off all the paint with thinners and start again or refer to the manufacturer for advice.
Blisters
Mostly affecting exterior woodwork, blisters can vary in size from pin heads to large areas. The cause is moisture in the wood or on the surface, trapped between coats of paint, or there may be resinous knots in the wood. Another less common cause is painting over a soft, thick coat. The action of very strong sunshine when any of these conditions exist is likely to cause blistering.
Try to paint external woodwork towards the end of the summer when, ideally, it should have dried out completely. If this is not possible, try to paint in dry, warm conditions. Don’t paint immediately after rainfall or washing down, unless the surfaces are thoroughly dried off. Strip off any thick, soft paint and always apply knotting to all resinous areas after stripping back to bare wood.
Cut off the surface of the blister and with fine wet and dry glasspaper rub back to a sound surface or bare wood if blistering is extensive. Apply knotting and primer as necessary, fill depressions with fine surface filler and apply undercoat and top coat.
Runs, sags and wrinkles
Fine lines or drips on a painted surface result from bad application. Wrinkles are likely to occur on thick, sagging paint.
Do not overload the brush and always brush out each application before adding another. Look at the paint five minutes after application; it may still be possible to brush out any runs.
If you notice runs before the paint has started to dry, brush them out lightly; if paint is drying, you will smear the surface. Or treat as for Pimples.
Dull gloss
Dull finish occurs if thinners used wrongly, surface not properly primed or undercoated. undercoat not given time to dry or finish over brushed or painted in damp or frosty conditions.
Prepare thoroughly. Leave the undercoat to dry for the recommended time, avoid using a thinner in gloss paint and do not apply in damp or frosty weather conditions.
Allow the paint to dry, then rub down lightly with fine glasspaper, dust off and apply a new finishing coat.
Grinning
The colour of the previous coat shows through the dry paint film indicating another coat is needed. Grinning may also occur if you use the wrong undercoat, do not stir paint sufficiently, thin it too much or overbrush finishing coat.
Use the correct undercoat and the recommended number of finishing coats. Make sure you stir the paint according to the manufacturer’s instructions. Never brush out the finishing coat too far.
Apply extra finishing coats as needed.
Brush marks
These can be seen in the finished paint. The cause is insufficient rubbing down of the old paint surface, faulty application (applying the paint too thickly and not brushing out correctly) or using poor quality brushes.
Carefully prepare the surface, making sure poor paint is rubbed right back. Apply the paint evenly and finish brushing out in the direction of the grain. Slightly thin excessively thick paint and always use good quality brushes.