What does interior wall painting preparation actually involve?

Painting a wall well is mostly preparation. The sequence Selleys sets out has four stages: clean the walls, patch the holes and cracks, fill the gaps between trim and wall, then paint. Three products cover the first three stages — Selleys Sugar Soap, Selleys Spakfilla Rapid and Selleys No More Gaps Interior Multipurpose.

Time spent here is what makes a paint job last, because every one of these steps addresses a specific way that paint fails: it peels off greasy walls, it accentuates unfilled cracks, and it cracks along unfilled gaps as the building moves.

The guides in this section

• Why should you be preparing walls before painting? — the reasoning behind each preparation step, and what goes wrong when you skip it.
• How to prepare your walls for painting — the full step-by-step, with dilution rates, drying times and painting intervals.
• Repairing holes in the home — small holes, door-handle holes, large plasterboard holes and holes in doors, each with its own filler.
• How to fill gaps around windows — stopping draughts around window frames.
• How to fill gaps between skirting boards and walls — getting a seamless line between trim and wall.

Stage 1 — Clean

Dust, dirt and grease compromise paint adhesion, which shows up as uneven coverage and, later, peeling or bubbling. Selleys Sugar Soap removes grime and leaves a clean surface to paint onto.

Check which sugar soap you have, because the dilution differs. Selleys Original Sugar Soap (750 mL, makes up to 30 litres) is diluted at half a cup into half a bucket — 5 litres — of water. Original Sugar Soap Super Concentrate (1 L, makes up to 80 litres) is diluted at half a cup into a full 10 litre bucket. Either can be used neat on stubborn or in-ground marks with a non-scratch scouring sponge.

On walls and ceilings there is no need to rinse. Wipe it off aluminium and brass immediately, rinse it well off glass before it dries, and rinse floors, baths and shower recesses well after use. Rubber gloves are recommended for sensitive skin — the product has a pH of around 11 and causes serious eye irritation.

Stage 2 — Patch

Whether it is minor dents, nail holes or larger cracks, Spakfilla Rapid is the fast option for patching and repairing. It is a ready-mixed, lightweight filler that is fast-drying, virtually non-shrinking and non-cracking, and it needs only one application. It is moisture and mould resistant, easy to sand, and suitable for wallboard, wood, masonry, plaster, primed nail heads and plasterboard.

The drying time depends entirely on thickness: 30 minutes for less than 2 mm, 24 hours for more than 2 mm. That single distinction explains most complaints about fillers "not drying". A nail hole is a 30 minute job; a deep patch is an overnight one.

Spakfilla Rapid can be painted with water-based paints once set, and needs 24 hours before oil-based paints. It is not for load-bearing use, should not be nailed, and should not be used where load or compression occurs — behind a door where the knob touches the wall, for example, the filler may be crushed. Where movement occurs, use No More Gaps instead.

Stage 3 — Fill the gaps

No More Gaps Interior Multipurpose fills the gaps between skirting boards, window frames and plaster walls, giving a seamless transition between surfaces. It is water-based, formulated to cope with building movement so the finish does not crack, and it has a skin time of 20 minutes with a movement capability of ±15% (ISO 9046).

Allow around 30 minutes before painting with water-based paint, and 24–48 hours before oil-based paints. Longer drying is needed for flat and ceiling paints, which are highly filled and flex less than other paints. To avoid the paint cracking, apply to gaps no larger than 5 mm deep and 10 mm wide, at temperatures above 10°C, and do not apply the paint too thickly.

It is not suitable for permanent water immersion or constantly damp areas, and it is not for gaps between tongue-and-groove boards or weatherboards — No More Gaps Exterior is the product for those.

Stage 4 — Paint

Two coats is usually ample, but use an undercoat if you are painting a light colour over a dark one. Follow the paint manufacturer's own recoat times.

Common questions about paint preparation

Do I really need to wash the walls?

Yes. Modern paints adhere to most surfaces, but they stick best to smooth, clean ones. A dirty, oily or greasy surface risks the paint peeling or bubbling once dry, and dust makes the finish look mottled rather than smooth.

How do I dilute sugar soap?

Original Sugar Soap: half a cup into half a bucket (5 litres). Super Concentrate: half a cup into a full 10 litre bucket. Check which one you have bought.

Do I need to rinse the walls afterwards?

On walls and ceilings, no. Rinse glass before the product dries, wipe it off aluminium and brass immediately, and rinse floors, baths and shower recesses well.

Which filler for a nail hole?

Spakfilla Rapid. At less than 2 mm it dries in about 30 minutes.

How long before I can paint over filler?

Spakfilla Rapid: 30 minutes at under 2 mm with water-based paint, 24 hours at over 2 mm, and 24 hours before oil-based paints.

What is the difference between a filler and a gap filler?

A filler such as Spakfilla is rigid and sands smooth — right for holes in a solid surface. A gap filler such as No More Gaps stays flexible — right for the joint between two materials that move relative to each other, like a skirting board and a wall.

Why does the paint keep cracking along my skirting line?

Usually because the joint moves and the filler in it cannot. Use a flexible gap filler, keep the gap no larger than 5 mm deep and 10 mm wide, apply above 10°C, and do not lay the paint on too thickly.

How long before painting over No More Gaps?

Around 30 minutes for water-based paint and 24–48 hours for oil-based paints. Flat and ceiling paints need longer still.

Do I have to sand?

Sanding removes bumps, old roller lint and rough spots, and it gives the paint a keyed surface to hold on to, so it is less likely to flake.

Can I paint over flaky paint?

No — it will peel or bubble. Peeling paint usually means poor adhesion between the wall and the previous coat, and painting over it hides the problem rather than fixing it.

Is exterior preparation any different?

The principle is the same: clean, sand and fill before repainting. Weatherboards in particular need old flaky paint removed so the new coat has a clean surface to adhere to. Use exterior-rated products for the filling and gap filling.