Wall Preparation: The Step-by-Step Checklist Before You Paint

Ask any professional decorator what separates a paint job that lasts a decade from one that peels in a year, and they will all say the same thing: preparation. Roughly eighty percent of a good paint job happens before the tin is even opened. The good news is that none of the steps are difficult — they just have to be done, and in the right order.

The preparation checklist

Work through these steps in sequence. Skipping one to save time almost always costs more time later.

1. Clear and protect the room

Move furniture to the middle of the room and cover it with dust sheets — proper canvas ones, not plastic, which tears and slides. Take down curtains, blinds, pictures, socket covers and switch plates. The hour this takes saves hours of cutting around obstacles and repairing drips later. Use low-tack painter's tape along skirting boards, door frames and ceiling edges; remove it while the final coat is still slightly tacky to avoid peeling the new paint.

2. Clean the walls thoroughly

Paint will not stick to dust, grease or grime. Wash walls from the bottom up with warm water and a squirt of sugar soap or mild detergent — working top-down can leave streaks that show through the finish. Pay particular attention to the areas around light switches, cookers and radiators, where invisible grease builds up. Rinse with clean water and let the walls dry completely. A surface that feels clean to the hand is not the same as one that is clean enough to paint.

3. Scrape loose and flaking paint

Run a scraper over every wall and prise off anything that is loose, blistered or peeling. Paint applied over flaking old paint will peel with it, so this step is non-negotiable. Where old paint is sound but glossy, dull it with a light scuff sand using 180–220 grit paper so the new coat has something to key into. You do not need to sand back to bare plaster — just remove the shine.

4. Fill cracks, holes and dents

Use a flexible acrylic filler for hairline cracks (they will move with the building) and a powder joint compound or two-part filler for deeper damage. Press the filler in slightly proud of the surface, let it dry fully, then sand it flush. For a really invisible repair, "spot prime" each filled area before painting so it does not show through as a dull patch. Hairline cracks in plaster often return unless the underlying cause — usually settlement or movement — is addressed, so fill them with something flexible rather than rigid.

5. Treat stains and damp

Water stains, nicotine, marker pen and grease will bleed through ordinary paint within days. Seal them with a stain-blocking primer — oil-based or shellac-based blockers are the most reliable. Critically, never paint over an active damp problem. If a wall is wet, find and fix the source of moisture first (a leaking pipe, rising damp, failed damp-proof course) and let the wall dry out completely. Paint on a damp wall will blister and peel no matter how good the preparation.

6. Sand the whole wall lightly

Once all repairs are done and dry, give the entire wall a light overall sand with fine paper. This removes the last specks of high-spot filler, opens the surface of any existing paint and gives the new coat a uniform key. Hoover the walls down afterwards — yes, with the vacuum cleaner and a soft brush head — to remove every grain of dust. Dust is the enemy of a smooth finish.

7. Prime bare or repaired areas

Bare plaster, large filled areas and patches of bare drywall need a mist coat or primer before the topcoat goes on. For new plaster, a "mist coat" — the same emulsion thinned with about 10% water — seals the surface and exposes any remaining defects. For filled repairs, a primer stops the filler sucking the moisture out of your topcoat and leaving a flat, dull patch.

8. Tape off and protect surfaces

Finally, apply low-tack tape to every edge you cannot reliably cut by hand: along the ceiling line, around window frames, against skirting boards and around any fittings. Press the tape down firmly along its entire length — a poorly seated edge lets paint bleed underneath and creates more cleaning up than it saves. Remove the tape at a 45° angle while the paint is still slightly wet for the cleanest line.

How long does preparation take?

For a typical medium-sized room with sound existing paint, expect to spend a full day on preparation for every day of painting. For a room in poor condition — heavy cracks, water stains, peeling paint — preparation can take twice as long as the painting itself. This is not wasted time; it is the difference between a finish you are proud of and one you keep noticing the flaws in.

Once the walls are clean, sound, dry and primed, the painting itself becomes the easy part — and you will get an accurate paint quantity from the calculator because you are painting a known surface rather than fighting a compromised one.