How to Prepare a Surface for Painting — Step-by-Step UK Guide

What You'll Need

Before You Start

• Clear the room as much as possible. Move furniture to the centre and cover with dust sheets. Remove curtains, light fittings (turn off at the consumer unit first), switch plates and outlet covers.
• Inspect every surface — look for cracks, holes, damp patches, mould, flaking paint, loose plaster, protruding nails and stains. Make a list of what needs attention.
• If the property is pre-1960, be aware that old paint may contain lead. Do not sand dry — use a chemical paint stripper or wet-sand to minimise dust. Consider professional testing if unsure.
• Use our Primer Coverage Calculator for primer quantities and our Paint Coverage Calculator for topcoat quantities.

Step-by-Step Instructions

Step 1: Protect the Room

Lay dust sheets over floors and furniture. Mask off areas you do not want to paint — window glass, carpet edges, fitted cupboards. Remove or mask light switches and sockets. Preparation creates a lot of dust — close doors to other rooms and open a window for ventilation.

Step 2: Wash All Surfaces

Wash walls and ceilings with sugar soap solution using a sponge, working from the bottom up (to avoid streaks). This removes grease, dirt, nicotine and cooking residue that prevent paint adhesion. Rinse with clean water and allow to dry fully. For kitchens and bathrooms, use a stronger sugar soap mix and pay extra attention to greasy areas.

Step 3: Remove Loose and Flaking Paint

Scrape off all loose, flaking or blistering paint with a stripping knife or scraper. Work carefully to avoid gouging the surface beneath. For large areas of failing paint, consider using a heat gun (not on lead paint) or chemical stripper to remove paint back to a sound surface. Feather the edges of any remaining paint with sandpaper so there is no visible step.

Step 4: Treat Mould and Stains

Treat any mould with a fungicidal wash — apply liberally, leave for the recommended time and rinse off. Do not use household bleach as it does not kill mould spores. For water stains, smoke damage or ink marks, apply a stain-blocking primer (e.g. Zinsser BIN or Coverstain) after the surface is dry. These stains bleed through standard paint.

Step 5: Fill Holes and Cracks

Fill nail holes, screw holes and small cracks with decorators filler using a filling knife. For deeper holes (over 5mm), build up in layers, allowing each to dry before adding the next. For cracks that may move (e.g. between ceiling and wall), use flexible decorators caulk instead of rigid filler. Use wood filler for timber surfaces — it sands better than general-purpose filler.

Step 6: Sand Smooth

Once filler is completely dry, sand all filled areas smooth using 120-grit sandpaper on a sanding block. Sand previously glossy surfaces (gloss paint, varnish) with 180-grit to key the surface for the new paint. For large wall areas, a pole sander speeds up the work. Wipe or vacuum all dust off after sanding.

Step 7: Caulk Gaps

Run a bead of decorators caulk along any gaps between skirting boards and walls, around architraves, along ceiling coving joints and at any other junctions. Smooth with a wet finger. Caulk fills minor gaps and creates a clean paint line. Allow 1-2 hours to dry before painting over.

Step 8: Prime Bare Surfaces

Apply the appropriate primer to all bare surfaces. For bare plaster: a mist coat (50/50 emulsion and water). For bare wood: a wood primer (or multi-surface primer). For stained areas: a stain-blocking primer. For metal (radiators, pipes): a metal primer. Allow primer to dry fully before topcoating — check the tin for drying times.

Step 9: Prepare Woodwork

Sand all woodwork (skirting, architrave, door frames, window frames) with 120-grit sandpaper to key existing paint for the new coat. Fill any dents or holes with wood filler, sand smooth and prime bare patches. Apply knotting solution to any resinous knots to prevent bleed-through. Wipe off all dust with a damp cloth.

Step 10: Final Dust-Down

Vacuum the room thoroughly — walls, skirting tops, window sills and floors. Wipe all surfaces with a damp cloth to remove any remaining dust. Dust settling on wet paint ruins the finish. The room is now ready for painting.

Surface-Specific Preparation Guide

Common Mistakes to Avoid

• Painting over dirt or grease: Paint will not adhere to greasy surfaces — especially in kitchens. Always wash with sugar soap first.
• Not sanding gloss surfaces: New paint will not stick to a shiny gloss finish. Always sand to create a key for the new coat.
• Filling with the wrong product: Standard filler cracks in moving joints — use flexible caulk. General filler does not sand well on wood — use wood filler.
• Painting damp surfaces: Paint over damp plaster or damp wood will blister and peel. Allow everything to dry completely before painting.
• Skipping primer on stains: Water stains, smoke marks and ink bleed through standard emulsion paint. Use a shellac-based stain blocker.

Cost Estimate (2026 UK Prices)

Use our Primer Coverage Calculator and Paint Coverage Calculator for exact quantities for your project.