How to Prepare Walls for Painting Properly

A fresh coat of paint cannot hide loose plaster, greasy marks or poorly filled holes for long. Learning how to prepare walls for painting is what gives a matt, satin or eggshell finish its clean appearance and helps it stay looking good after the room is back in use. The coating matters, but the wall underneath decides whether it adheres evenly, covers properly and resists peeling.

Preparation is not difficult, but it should be matched to the surface. A sound, previously painted bedroom wall needs a different approach from a newly plastered ceiling, a kitchen wall with cooking residue or a damp-prone exterior-facing area. Taking time at this stage also prevents wasted paint, repeat coats and visible repairs.

Check the wall before you buy paint

Start in good daylight and inspect the whole surface, not just the area at eye level. Run your hand across the wall to feel for raised paint edges, rough filler, loose paper or powdery patches. Look closely around radiators, switches, windows, skirting boards and ceilings, where cracks and stains are common.

Small nail holes, light scuffs and fine hairline cracks are normal preparation jobs. Larger cracks, recurring damp marks, soft plaster, bubbling paint or mould need the cause dealt with before painting. Paint applied over an active moisture problem may blister or discolour, whatever finish you choose. Repair leaks, improve ventilation or resolve penetrating damp first, then allow the wall to dry fully.

It is also worth identifying the existing coating. Most modern interior walls are finished in water-based acrylic paint, which can usually be cleaned, lightly sanded and recoated. Older glossy surfaces, oil-based coatings and unknown finishes need more attention because new paint can struggle to grip them. If you are unsure, test a discreet patch with your planned primer and topcoat.

Protect the room and remove obstacles

Move furniture away from the walls or cover it with clean dust sheets. Take down pictures, hooks where practical, blinds and removable shelves. Switch off power before removing faceplates from sockets and switches, and mask the edges if they must remain in place.

Use low-tack masking tape along skirting boards, door frames, window frames and fittings that will not be painted. Press it down firmly, but avoid leaving tape on fresh paint for too long. A clean working area lets you roll closer to edges with confidence and stops dust or fibres getting into the coating.

Clean the surface thoroughly

Paint does not bond well to dust, grease, smoke residue or household polish. This is especially relevant in kitchens, hallways, utility rooms and around radiators. Even walls that look clean can carry a fine film that causes patchy coverage or poor adhesion.

For normal interior dirt, wipe the wall with warm water and a mild detergent or suitable sugar soap solution. Work from the bottom upwards to reduce streaking, then wipe again with clean water if the cleaner requires rinsing. Use a non-abrasive sponge or cloth rather than soaking the wall. Allow it to dry completely before filling, sanding or priming.

Mould should not simply be painted over. Treat it with an appropriate mould remover, following the product directions and ventilation guidance, then remove any loose coating. Once the source of condensation or moisture is controlled, use a suitable stain-blocking or anti-mould primer where needed before applying the finish coat.

Remove loose paint and defective material

Any coating that is flaking, blistering or lifting from the wall must come off. Scrape gently with a filling knife or paint scraper, holding the blade at a shallow angle to avoid gouging the plaster. Do not stop at the obvious loose patch: continue until the remaining paint has firm edges and will not lift further.

Feather the edge between bare areas and sound paint with medium-grit abrasive paper. The aim is not to strip every wall back to bare plaster. It is to remove failure and make transitions invisible once painted. A sanding block gives better control on flat walls, while a flexible sanding sponge is useful around corners and mouldings.

If the existing paint is very glossy, lightly abrade the full surface to create a key for primer or the next coat. Wipe away all sanding dust with a vacuum fitted with a soft brush attachment, followed by a clean, dry microfibre cloth. Dust left on the wall becomes trapped in the paint and can reduce adhesion.

Fill holes, cracks and uneven areas

Choose a filler that suits the repair. Lightweight ready-mixed filler works well for shallow nail holes and small dents, while a deeper repair filler is better for larger holes and damaged plaster. For fine cracks, open the crack slightly with the edge of a filling knife first. This creates enough space for filler to bond instead of sitting on the surface.

Apply filler in thin layers, pressing it firmly into the repair. Overfill only slightly, as excess material means more sanding later. Deep holes may need two or more applications, with drying time between each layer. Follow the stated drying times rather than judging by the surface alone, particularly in cool or humid rooms.

When dry, sand the repair smooth and run your fingertips over it. Your hand will find ridges that your eyes miss. Shine a work light across the wall at a shallow angle if you want to check the finish carefully. This is particularly useful before applying a low-sheen matt paint, which can still show poor preparation when light falls across it from a window.

When to prime walls before painting

Primer is not always required on sound, previously painted walls that are clean, dull and similar in colour to the new finish. However, it is the right step when the surface is bare, porous, repaired, stained, very dark, glossy or uneven in absorbency.

New plaster must be fully dry before coating. It should look uniformly pale with no darker damp areas. Apply a mist coat made from a suitable water-based matt emulsion diluted according to the paint manufacturer’s instructions, or use a dedicated plaster primer. This seals the surface without forming a weak skin that could peel later.

Spot prime filler repairs and bare patches when they are small. If repairs cover a large section of the wall, priming the whole area is usually the better option because it creates an even base for the finish. Without this step, porous filler can absorb paint differently and leave dull, flashing patches after drying.

Use a stain-blocking primer for water marks, nicotine, smoke staining, tannin bleed or other discolouration. A standard acrylic wall paint may cover a stain at first, but it can bleed through again as the coating dries. For glossy or difficult surfaces, choose an adhesion primer designed for the substrate rather than relying on extra coats of finish paint.

Choose the right finish for the room

Preparation and paint selection work together. A durable acrylic wall paint is practical for high-traffic spaces such as hallways and family rooms. A washable satin or soft-sheen finish suits kitchens and utility areas where marks need regular cleaning, while a quality matt finish is often preferred for living rooms and bedrooms because it gives a softer, lower-reflective appearance.

For ceilings, use a ceiling paint formulated to minimise splatter and provide even coverage. In bathrooms, choose a moisture-resistant coating and make sure the room has adequate extraction. No paint can compensate for persistent condensation from poor ventilation.

Buy enough paint from the same batch or have the full quantity mixed at once for consistent colour. Midi Decor offers surface-specific primers, undercoats, acrylic paints and accessories so you can match the preparation products to the topcoat rather than making do with a general-purpose coating.

Final checks before the first coat

Before opening the paint, make sure the wall is dry, smooth and free from dust. Check that filler repairs have disappeared into the surrounding surface and that all masking is secure. Stir the paint thoroughly, especially after storage, and pour only what you need into a clean tray.

Cut in around edges with a good-quality brush, then use a roller with a sleeve suited to the wall texture. Apply paint in manageable sections, maintaining a wet edge to avoid lap marks. Do not try to achieve full opacity with one heavy coat. Two controlled coats, with the stated drying time between them, normally give a more even and durable result.

Remove masking tape carefully while the final coat is still slightly tacky, pulling it back on itself at a low angle. Then leave the room as undisturbed as possible while the paint cures. A wall that has been cleaned, repaired, sanded and primed correctly gives every finish the best chance to perform exactly as it should.