Paint problems: 12 defects, their causes and how to fix them

The 12 cases

From defect to fix

1. 01

   Roller marks and visible joins on a matt wall

   Cause. A very matt paint shows every change in film thickness. Marks appear when you go back over a band that has started to dry, when the roller is alternately soaked and dry, when you criss-cross in every direction right to the end, or when the room is warm and draughty and the paint sets too fast.

   Fix. If it is still wet: stop and let it dry 3 to 4 hours. Lightly sand the ridges with 180–240 grit, dust off, then apply one full coat, top to bottom in one-metre bands, laying off each band in a single direction without going back. Heating off, windows closed while you paint. The full method is in How to paint a wall without marks.

2. 02

   Patches that are matter or shinier than the rest, and touch-ups that show

   Cause. The surface absorbs paint unevenly: a filled crack, a repaired ceiling, unprimed new plaster drink the binder and leave a duller patch. A local touch-up on a matt does the opposite, a shinier or darker patch.

   Fix. Prime the whole surface, not just the repair, then finish corner to corner. For a touch-up on a recently painted wall, use the same tin and the same tool, feathering the edges dry. On a wall painted years ago the shade has drifted: repaint the whole wall.

3. 03

   The colour is not the one on the card or the sample

   Cause. Almost always one of four: a single coat, which lets the ground influence the shade; an old coloured wall showing through; a different finish from the one tested (the same colour looks lighter in satin than in matt); or the room's light, which no card can anticipate.

   Fix. Wait for the second coat to dry before judging. If the ground was dark or strongly coloured, a tinted primer and a third coat settle it. For next time, our method for testing a colour at home avoids the surprise.

4. 04

   The paint will not cover, the ground still shows

   Cause. Going from a dark colour to a light one without primer; saturated reds, yellows and oranges, whose pigments are naturally less opaque; over-thinned paint; a wrung-out roller stretching the film.

   Fix. Our tinted primers (Red, Dark Red, Yellow, Light Grey, Dark Grey…) exist for exactly this: one coat of primer matched to the shade often replaces a third coat of finish. Thin barely, and load the roller normally. Allow 0.5 L of primer per 1 L of paint.

5. 05

   Blisters and bubbles

   Cause. Moisture under the film: an exterior wall taking in water, plaster or render not yet dry, a bathroom without ventilation, or paint applied to a hot surface in full sun. More rarely, a greasy or dusty ground the paint never bonded to.

   Fix. Deal with the source of damp first, or the blisters come back. Scrape, let it dry completely (several weeks for new plaster), prime and repaint with a breathable finish — Marble Matt Emulsion and Masonry Paint let water vapour through; a sealed film traps it.

6. 06

   Paint flaking or peeling

   Cause. A bonding failure: old gloss or oil-based paint left unsanded, a chalking coat, a dusty surface, bare wood or metal without primer, or the damp of the previous case.

   Fix. Scrape everything that lifts, sand back to a sound, matt ground, vacuum then wipe with a damp sponge, apply the right primer — Multi-Surface Primer on wood and metal, Wall Primer under emulsions — then two thin coats. Our woodwork preparation page covers the sanding.

7. 07

   Cracking and crazing

   Cause. A coat too thick, drying on the surface before the core; a second coat laid on a first still wet; new plaster painted too soon; or temperature swings during drying.

   Fix. Sand back to a sound ground, prime, then two thin coats respecting the 3 to 4 hours' recoat time at 20 °C — longer if cold or damp. On new plaster, wait two to four weeks before the first coat.

8. 08

   Runs and drips

   Cause. Too much paint in one pass, especially in satin and gloss, which are more fluid; an overloaded brush in a moulding; a door painted upright without picking up the edges.

   Fix. Wet: lay off immediately with an almost dry brush, along the grain or top to bottom. Dry: let it harden 24 hours, sand the run flush with 240 grit, dust off, repaint thinly.

9. 09

   Orange-peel or lumpy texture

   Cause. A roller pile too long for a satin or gloss finish; paint too cold or too thick; rolling too fast and trapping air; an opened tin that has skinned.

   Fix. Short pile (5 to 8 mm) for satins and glosses, medium pile (10 to 12 mm) for wall matts. Paint between 15 and 25 °C, thin very slightly with water if the paint drags, and strain an opened tin. Then sand the area fine and apply one more coat.

10. 10

    Stains and rings that keep coming back

    Cause. Migrating stains: nicotine, soot, water damage, tannin from a wood (oak, cedar) or a knot, marker ink. They bleed through an ordinary water-based paint coat after coat.

    Fix. Clean, let dry, then seal the stain with a blocking primer — our Stabilising Primer on chalky or stained grounds — before the finish. Repainting without sealing only postpones the ring.

11. 11

    Grit and dust in the film

    Cause. A wall dusted with a dry cloth, which redistributes the dust; a new roller shedding fibres; a skinned tin not strained; sanding dust left in the corners.

    Fix. Vacuum walls and skirtings, wipe with a damp sponge, let dry. Roll a new roller over masking tape to lift loose fibres. Strain the paint into a clean tray. A dried nib sands out with 240 grit and disappears under the next coat.

12. 12

    A lingering smell and slow drying

    Cause. Our paints are water-based: they dry by evaporation, so slowly in a cold, damp or closed room, and slower still in thick coats.

    Fix. Paint between 15 and 25 °C, air the room before and after application (not during, to keep the wet edge), allow 3 to 4 hours between coats. The light smell of a low-VOC water-based paint usually clears within a day or two of ventilation; the film itself takes 2 to 4 weeks to harden fully — clean gently until then.