Preparing walls for painting properly

Washing down first

Grease around light switches, kitchen splashback areas and general household grime all resist new paint if left in place, causing poor adhesion and visible patches once the coating dries. A sugar soap wash followed by a clean water rinse removes surface contamination before any filling or sanding begins, and it takes far less time than dealing with a failed coat later. Nicotine staining and smoke residue on older ceilings need the same treatment before painting, and in more severe cases a stain-blocking primer as well, since new emulsion applied straight over nicotine staining will often let the yellow-brown tint bleed back through within weeks.

Filling cracks and holes properly

Hairline cracks, nail holes and old fixing points all need filling with an appropriate filler, left to cure fully, then sanded flush. Rushing this stage by painting over damp filler is one of the most common causes of cracking reappearing within months. Larger cracks in older plaster sometimes need a flexible filler or a scrim tape reinforcement rather than a rigid filler that will simply crack again with normal building movement.

Sanding for a level, keyed surface

Sanding smooths filled areas flush with the surrounding wall and gives a slight key for the next coat to grip. It needs to happen after every filling stage, not just once at the end, because a filler that looks flush wet can shrink slightly and telegraph through a glossy finish once dry. Dust-extracted sanding keeps this stage manageable in occupied rooms.

Stabilising powdery or friable surfaces

Old distemper, chalky masonry and powdery plaster will not hold a new coating without treatment first. A stabilising solution binds loose material to the substrate so the primer and subsequent coats have something solid to adhere to, rather than sitting on a surface that will eventually flake away and take the new paint with it.

• Test for chalking by wiping a dark cloth across the surface
• Apply a stabilising solution and allow full cure time
• Avoid painting directly onto untreated distemper
• Re-test adhesion before proceeding to primer

Priming bare and repaired areas

Bare plaster, new filler and any exposed timber all need an appropriate primer or mist coat before the finish system goes on, because these materials are more porous than the surrounding painted surface and will otherwise flash through as a different sheen once topcoat is applied. Skipping primer on repaired patches is one of the most common reasons a wall looks patchy under raking light even after two full coats.

Dust control during preparation

Sanding produces fine dust that settles on every surface in the room if left unmanaged, and in occupied homes or offices that dust becomes a genuine nuisance beyond the working area. Dust-extracted sanders, sheeted floors and closed doors between the working area and the rest of the property keep the disruption contained and make final clean-up far quicker. In kitchens and rooms with sensitive electronics or soft furnishings that cannot easily be removed, additional dust sheeting and, where practical, temporary zip-wall containment help keep fine particles away from surfaces that are difficult to clean afterwards.

• Use dust-extracted sanders wherever possible
• Sheet floors and furniture before sanding begins
• Close doors to unaffected rooms
• Vacuum surfaces before the next coat rather than dusting

Sound versus unsound substrates

Before any filling or sanding begins it is worth establishing whether the wall itself is structurally sound, because no amount of preparation fixes plaster that is genuinely blown or detached from the background. Tapping a suspect area and listening for a hollow sound, or pressing gently to feel for movement, tells you whether you are dealing with a cosmetic repair or something that needs re-plastering before painting can start. Painting over blown plaster only delays the problem and wastes the cost of the coating applied on top of it, since the plaster will eventually fail and take the paint with it regardless of how well the finish coats were applied.

Why prep decides the finish

Two coats of good paint over poor preparation will always look worse than two coats of ordinary paint over excellent preparation. Raking light from windows and downlights exposes every unfilled crack and unsanded ridge, so the areas most visible to a client are exactly the areas most punished by skipped preparation. Time spent here is the single best investment in the final look of a job, and it is also the stage most often shortened when a quote is squeezed on price, which is worth remembering when comparing two very different figures for what looks like the same job on paper.