How to Prepare Walls for Painting: A Professional Guide

Why Preparation Matters More Than Paint

In twenty years of decorating London's finest homes, we've learned that 70% of a paint job's longevity comes down to what happens before the first coat of paint goes on. The most expensive Farrow & Ball paint in the world will peel, flake, or crack within months if applied over poorly prepared surfaces.

This guide walks through the preparation process our teams follow on every project, whether it's a single bedroom in a Kensington flat or a full townhouse restoration in Mayfair.

Stage 1: Surface Assessment

Before any tools come out, we conduct a thorough assessment of every surface to be painted. We're looking for:

• Cracks — hairline cracks are normal in London properties, especially in older buildings that move seasonally. Structural cracks (wider than 3mm, diagonal, or stepping across brickwork joints) need investigation by a surveyor before any decorating work begins.
• Damp — rising damp, penetrating damp, and condensation each require different treatments. Paint will not adhere to damp surfaces. We use moisture meters to check readings and won't proceed until the underlying issue is resolved.
• Previous paint condition — flaking, bubbling, or chalking paint must be removed entirely. Sound, well-adhered paint can be painted over after proper keying.
• Substrate type — bare plaster, previously painted surfaces, lining paper, woodchip, artex, and skim coat each require different preparation methods.

Stage 2: Protection

Before any preparation begins, we protect everything that isn't being painted:

• Heavy-duty cotton dust sheets over all floors (not polythene, which is slippery and doesn't absorb drips)
• Furniture moved to the centre of the room and covered
• Light switches, sockets, and door furniture masked with low-tack tape
• Carpets protected with self-adhesive film along skirting boards

Stage 3: Washing

This step is frequently skipped by DIY painters and even some trade decorators, but it's critical. Walls accumulate grease, dust, nicotine, and airborne cooking residues over time. Paint applied over these contaminants will lose adhesion.

We wash all surfaces with a sugar soap solution, working from the bottom up to avoid tide marks. Kitchen walls may require multiple washes. We allow surfaces to dry completely — typically 24 hours — before proceeding.

Stage 4: Stripping (If Required)

If existing paint is in poor condition, it must be removed. Our approach depends on the substrate:

• Flaking emulsion on plaster — scraped with a broad scraper, then sanded to feather the edges
• Multiple layers of old gloss on woodwork — heat gun or chemical stripper (we prefer Peelaway for heritage properties as it captures lead paint safely)
• Wallpaper removal — scored, soaked, and stripped. Vinyl wallpaper requires the top layer to be peeled before the backing can be soaked. We use steamers for stubborn papers.
• Woodchip or textured coatings — soaked and scraped, then any remaining texture is skimmed smooth

Stage 5: Filling and Repair

With clean, sound surfaces exposed, we fill all imperfections:

• Hairline cracks — flexible filler (Toupret or similar) that moves with the building
• Larger cracks and holes — two-part filler applied in layers, sanded between coats
• Missing or damaged plaster sections — re-plastered by our team or a specialist plasterer, then left to cure for the recommended period (typically 4-6 weeks for a full skim coat)
• Woodwork defects — two-part wood filler for deep repairs, fine surface filler for minor imperfections

Stage 6: Sanding

Every filled area and every previously painted surface needs sanding to create a mechanical key for the new paint. We use:

• 120-grit paper for general wall surfaces
• 240-grit paper for fine finishing on woodwork
• Festool extraction sanders for dust-free sanding — essential in occupied properties and for the health of our team

After sanding, all surfaces are wiped down with a tack cloth to remove fine dust particles.

Stage 7: Priming

The primer coat is the foundation of your paint system. Different surfaces need different primers:

• Bare plaster — a mist coat of diluted emulsion (typically 70:30 paint to water) to seal the surface and prevent the plaster from drawing moisture from the topcoats
• Stained surfaces — Zinsser BIN shellac-based primer to lock in water stains, nicotine marks, and tannin bleed
• Bare timber — Zinsser Bulls Eye 1-2-3 or an alkyd-based wood primer depending on the topcoat system
• Previously painted surfaces in good condition — may not need a separate primer, but benefit from a dedicated undercoat for colour change

The Difference Professional Preparation Makes

We've seen countless properties where previous decorators cut corners on preparation. The paint looks fine for a few months, then gradually the cracks reappear, the finish starts to look dull, and eventually flaking begins. A properly prepared and painted room should look fresh for seven to ten years in normal domestic use.

If you're considering a painting project and want to understand what level of preparation your property needs, we offer free assessments with no obligation.