A freshly painted room can look completely different in a day, but the finish is decided long before the first coat goes on. Knowing how to prepare walls for painting means dealing with the small issues that paint will otherwise highlight: hairline cracks, dusty surfaces, dents, stains and rough patches around old repairs.

Paint does not hide poor preparation. In fact, a new coat often makes imperfections more noticeable, particularly in rooms with strong daylight or darker colours. Taking the time to prepare the surface properly gives you a smoother result, better adhesion and a finish that lasts.

Start by checking the wall condition

Before moving furniture or opening a tin of paint, inspect the walls in good natural light. Look along the surface from different angles, as this makes raised filler, uneven plaster and roller marks easier to spot. Run a clean hand gently across the wall too. If it feels gritty, powdery or uneven, it needs attention before painting.

Common problems include nail holes, picture-hook marks, cracks around doors and windows, flaking old paint, damp staining and loose wallpaper adhesive. These need different solutions, so avoid treating every mark with a quick coat of paint.

If you see a brown water stain, for example, first make sure the cause of the leak or condensation has been resolved. Painting over an active damp issue will not fix it. Once the area is dry and stable, it may need a stain-blocking primer before the topcoat. For widespread peeling, bubbling paint or crumbling plaster, it is worth getting professional advice rather than covering up a failing surface.

Protect the room before preparing walls for painting

Preparation work creates more dust and mess than most people expect. Move furniture out where possible. Larger pieces can be placed in the centre of the room and fully covered with clean dust sheets or protective plastic. Floors should be covered securely, especially carpets, timber flooring and finished tiles.

Remove switch plates, socket covers, curtain fittings and radiator covers where it is safe and practical to do so. If you prefer not to remove them, mask carefully around the edges. Keep the power off when working near electrical fittings and do not allow filler, water or paint to enter sockets.

Mask skirting boards, architraves, window frames and any surfaces that are not being painted. Good-quality masking tape helps create neat lines, but it should be applied to clean, dry surfaces and removed before the paint has fully hardened. Leaving tape on for too long can pull away fresh paint or leave adhesive behind.

At Adam Klos Painter & Decorator, protecting floors, furniture and adjoining surfaces is treated as part of the job, not an optional extra. It keeps disruption down and lets the decorating work move forward cleanly.

Clean away grease, dust and residue

Even a wall that looks clean can carry a fine layer of dust, cooking grease, smoke residue or household polish. Paint applied over contamination may dry unevenly or fail to bond properly.

For most interior walls, wipe the surface with warm water and a suitable sugar soap solution, following the product instructions. Pay extra attention to kitchens, hallways, around light switches and behind radiators, where grime tends to build up. In bathrooms, check for mould and treat it with an appropriate mould remover before painting. Wear gloves, ventilate the room and allow treated areas to dry fully.

After washing, rinse where required and leave the walls to dry completely. This is not a stage to rush. Painting onto a damp wall can cause poor adhesion, blistering and patchy colour. Once dry, remove any remaining dust with a vacuum and soft brush attachment, or wipe down with a clean, lint-free cloth.

Repair cracks, holes and damaged plaster

Small repairs make a big difference to the finished appearance. Remove loose material from cracks and holes first. A scraper or filling knife is useful for lifting flaky paint and opening up a crack slightly so the filler has a sound surface to grip.

Use a suitable ready-mixed or powder filler for shallow holes, minor cracks and dents. Press it firmly into the damaged area, then smooth it slightly proud of the wall. Filler can shrink as it dries, so deeper holes may need two or more applications rather than one thick layer.

For recurring cracks, particularly around door frames, windows or plasterboard joints, use a flexible decorator’s filler or scrim tape where appropriate. A crack that keeps returning may be caused by movement, so a rigid repair alone may not hold. If cracks are wide, numerous or accompanied by loose plaster, seek a professional assessment before decorating.

Allow filler to dry for the full recommended time. Drying times vary with product depth, room temperature and humidity. A repair may feel dry on the surface while still being soft underneath, which can cause problems when sanding.

Deal with loose and flaking paint

Where old paint is lifting, scrape it back until you reach a firm edge. Sand the edge so it blends into the sound paint around it. Simply painting over flakes traps the problem underneath and the new paint is likely to peel in time.

If the old surface is very glossy, such as previous satinwood or oil-based paint, lightly abrade it to provide a key for the new coating. Clean off all sanding dust afterwards. The right primer can also be necessary when changing between paint types or painting over a difficult surface.

Sand for a smooth, even surface

Sanding is where repairs begin to disappear. Use fine or medium-fine abrasive paper, depending on the surface, and sand filled areas until they are level with the surrounding wall. Work carefully rather than aggressively. Over-sanding can leave a hollow that shows through the paint.

You may also need to lightly sand the wider wall if it has rough roller texture, old brush marks or a sheen that needs dulling down. Use a sanding block for better control on small areas. For larger rooms or extensive repairs, professional dustless sanding equipment can make the work cleaner and reduce airborne dust throughout the property.

Shine a work light across the wall after sanding. Side lighting reveals ridges and missed imperfections far better than looking directly at the wall. If a repair is still visible now, it will be even more visible after painting, so refill and sand it again if needed.

Prime problem areas before applying paint

Not every wall needs a full primer coat, but some surfaces benefit greatly from one. Bare plaster, fresh filler, repaired patches, stains and strong colour changes can all affect how the final paint looks and performs.

New plaster must be fully dry before decorating. This can take several weeks, depending on thickness and conditions. It should be painted first with a mist coat made from water-based matt emulsion diluted in line with the manufacturer’s guidance, or with a dedicated plaster primer. Applying undiluted paint directly to bare plaster can lead to poor adhesion and an uneven finish.

Spot-prime filler and repaired sections if they are likely to flash through the topcoat. Flashing is when patches absorb paint differently and appear duller or shinier than the rest of the wall. For nicotine, water or tannin stains, use a stain blocker designed for the issue. Ordinary emulsion alone is rarely enough to stop stubborn marks returning.

When painting a very dark wall a pale colour, a tinted primer or an extra undercoat can save time and produce a more consistent result. The trade-off is an additional step, but it is usually preferable to applying several uneven topcoats.

Check the surface one final time

Before painting, the wall should be clean, dry, sound and smooth. There should be no loose paint, visible dust, greasy residue or soft filler. Check that masked edges are secure and that the room is well ventilated, without being excessively cold or humid.

Take a final look in both daylight and artificial light. Colours can expose flaws differently depending on the time of day, especially on feature walls and in south-facing rooms. This last inspection is often what separates an acceptable job from a finish that looks carefully completed.

Good preparation takes patience, but it is the part of decorating that protects your investment in paint, time and your home. If the walls need more than straightforward filling and sanding, arranging a professional assessment before work begins can save a great deal of rework later.