How to Prepare Walls Before Painting? — A Professional Checklist

There is a reason professional decorators spend more time preparing walls than they do painting them. Knowing how to prepare walls before painting is what separates a finish that lasts five or more years from one that starts peeling within months. The preparation stage is where the quality of a paint job is won or lost. Skip it and you will have uneven coverage, visible cracks, and paint that starts to peel within months. Do it properly and the finish looks sharp, lasts years, and holds its color.

This is the checklist our team at Decoration Touch works through on every project — whether that is a single bedroom in Hampstead, a full flat refurbishment in Maida Vale, or a commercial refit in Westminster. It applies equally whether you are hiring a decorator or having a go yourself.

Step 1 — Clear and protect the room

Preparation starts before you touch a wall.
Move furniture to the center of the room and cover it with dust sheets. Remove socket covers, switch plates, curtain hooks, and picture hooks where you can. Cover the entire floor with dust sheets — not just the edges. Paint splashes travel further than most people expect, and dried emulsion on timber flooring or carpet is an avoidable headache.

Apply low-tack masking tape around any fixtures you cannot remove: window frames, architraves, radiators, and light fittings. Avoid standard parcel tape — it pulls paint off surfaces when you remove it. If you are painting ceiling and walls in the same session, tape the junction and remove the tape while the paint is still slightly wet for a clean edge.

Step 2 — Assess the existing wall condition

Walk the room and look at every surface in raking light — hold a torch or work light at an angle against the wall. Raking light reveals imperfections that are invisible under normal overhead lighting: cracks, dents, nail holes, rough patches, and areas where previous paint has lifted or bubbled.
Make a note of what you are dealing with. There are four conditions to look for:

• Hairline cracks — common in older London properties, particularly Victorian and Edwardian terraces that have settled over decades. These need filling before painting.
• Larger cracks or holes — anything wider than 2–3mm needs proper filler or, in more serious cases, a skim coat of plaster.
• Flaking or peeling paint — this needs to be stripped back before any new paint goes on. Painting over flaking paint simply seals the problem in and delays it by a few months.
• Damp patches or staining — these need to be investigated and resolved at source before decoration. Painting over active damp does not fix the problem; it hides it temporarily and makes it worse. If you have damp patches appearing on interior walls, our damp and plastering repair service is worth getting looked at first.

Step 3 — Strip old wallpaper (if applicable)

If you are painting over wallpaper, remove it. Painting over wallpaper is a shortcut that causes problems: the moisture in the paint causes the paper to bubble, seams become visible through the finish, and any future redecoration becomes far more difficult.
Score the wallpaper lightly with a scoring tool, then saturate it with warm water mixed with a small amount of washing-up liquid. Work in sections and allow the water to soak in for five to ten minutes before peeling. A wide scraper removes most of it cleanly. Once the paper is off, check the plaster surface underneath. Old London properties sometimes have walls where the plaster was never meant to be seen — it can be rough, powdery, or have adhesive residue that needs sanding back before painting.

Step 4 — Fill cracks, holes, and imperfections

Once the walls are bare and assessed, fill every imperfection before you pick up sandpaper.
For small nail holes and minor dents, ready-mixed filler applied with a flexible filling knife is sufficient. Press the filler in slightly proud of the surface — it shrinks slightly as it dries. Two thin coats are more reliable than one thick one.

For hairline cracks, use a flexible decorator’s caulk rather than rigid filler. Rigid filler in a crack that has movement will crack again. Decorator’s caulk stays flexible and moves with the wall. This is especially relevant in older properties where seasonal movement is common.

For larger holes — anything the size of a fist or bigger — the correct approach is a patch repair using bonding plaster or a proprietary repair product, followed by finishing plaster or a skim. At this scale, getting a plasterer in to assess it properly is worth the cost. A poorly patched large hole will show through even the best paint job.Once all filler is dry, run your hand across every filled area. If you feel a ridge or a bump, it needs sanding.

Step 5 — Sand all surfaces

Sanding is the step that most DIY decorators underestimate or skip. It is what allows the new paint to stick properly.
Use 120-grit sandpaper for general sanding of filled areas and previously painted surfaces. Sand in circular motions, then finish with straight strokes in one direction. For larger areas, a sanding pole speeds the work up considerably.
Pay particular attention to:

• All filled areas, sanded flush with the surrounding surface
• Any areas where old paint has a sheen (gloss-painted walls need to be keyed before repainting)
• Woodwork, skirtings, and architraves if they are being repainted
• Any areas where paint is slightly raised or uneven.
  
  After sanding, the walls will be dusty. Wipe them down with a damp cloth or a tack cloth and allow them to dry fully before moving to the next step.

Step 6 — Clean the walls

Paint does not adhere well to greasy, dirty, or dusty surfaces. Even walls that look clean often have a layer of grease, household dust, or nicotine residue that needs removing.

Wash walls with a solution of sugar soap and warm water, working from the bottom up (to avoid dirty water running down an already-cleaned surface). Pay extra attention to areas around light switches, door handles, and anywhere hands regularly touch the wall.

Rinse with clean water and allow the walls to dry completely. In London homes with limited ventilation, allow at least 24 hours for walls to dry after washing before priming.

Step 7 — Apply primer or mist coat

Priming is not optional — it is what seals the surface, improves adhesion, and ensures your topcoat covers evenly. The type of primer depends on the surface you are painting:

Surface condition	Recommended primer
Fresh plaster	Diluted emulsion mist coat (3 parts paint : 1 part water)
Previously painted walls in good condition	Multipurpose water-based primer
Walls with staining or tannin bleed	Stain-blocking primer (shellac or oil-based)
Bare wood	Wood primer or aluminium oxide primer
Previously gloss-painted walls	Adhesion primer after sanding

New plaster is the most common mistake: applying standard emulsion directly to fresh plaster seals the surface before it has finished breathing and causes the paint to peel. Always mist-coat fresh plaster first and allow it to dry before applying topcoats.

Apply primer evenly and allow it to dry according to the manufacturer’s instructions — typically two to four hours for water-based primers, longer in cool or humid conditions.

Step 8 — Final check before painting

Once the primer is dry, do a final inspection before you open the topcoat.

Run your hand across every surface again. Any small imperfections that were invisible before priming will now show clearly — primer has a way of revealing what filler has missed. Light-sand any remaining bumps with 180-grit paper, dust off, and spot-prime those areas again.

Check all masking tape is still well-adhered and there are no gaps at the edges. Check that the room is at a stable temperature — below 10°C and most water-based paints will not cure properly; above 30°C and they dry too fast and streak.

If everything checks out, you are ready to paint. Knowing how to prepare walls before painting properly means accepting that preparation time will always exceed painting time on any well-executed project.

The professional checklist at a glance

• Furnitures moved and covered with dust sheets
• Floor protected, sockets and switches removed or taped
• All walls assessed in raking light
• Wallpaper stripped (if applicable)
• All cracks and holes filled (caulk for hairlines, filler for holes)
• All filled areas sanded flush
• All surfaces sanded to key the finish
• Walls washed with sugar soap and fully dried
• Primer or mist coat applied and dried
• Final inspection and spot repairs done

Need a professional to handle the preparation and painting?

Wall preparation done properly takes time — typically one to two days for an average room before a brush touches the topcoat. If you would rather hand the whole project over to a team that does this every day, get in touch with Decoration Touch. We cover Hampstead, Maida Vale, Westminster, Shepherd’s Bush, Kilburn, and Acton, and every project starts with preparation that does the job justice.

Frequently asked questions