Painting a London Kitchen Extension: Bi-Folds, Steelwork & New Plaster

Why Kitchen Extensions Need a Different Approach

Kitchen extensions are now the single most common building project on London terraced and semi-detached houses. From Belgravia basements to Chelsea side-returns and Battersea rear extensions, the brief is usually the same: knock through, install bi-fold or sliding doors, add a steel beam, and create an open-plan kitchen-diner flooded with natural light.

The painting and decorating work that follows is more complex than most homeowners anticipate. You are dealing with freshly plastered walls that contain moisture, exposed structural steelwork that requires specialist priming, new timber or aluminium bi-fold frames, and a room that will be subject to cooking steam, condensation and temperature swings for decades to come. Getting the specification right at this stage saves considerable trouble later.

Dealing with New Plaster

New plaster is the first challenge. A freshly skimmed wall in a London kitchen extension contains a significant amount of water — and that water needs to escape before you apply a full paint system. The general rule is to allow a minimum of four weeks drying time per coat of plaster, though in practice it depends on the time of year, the ventilation in the space, and whether underfloor heating or radiators are operational.

If you paint too soon with a standard vinyl emulsion, you create a vapour barrier. The moisture trapped behind the paint film causes adhesion failure — the paint bubbles, flakes, or develops damp patches weeks or months after completion.

The correct approach is to apply a mist coat first. This is a heavily thinned coat of matt emulsion — typically diluted at a ratio of around 70 per cent paint to 30 per cent clean water — which soaks into the plaster surface and provides a key for subsequent coats without sealing in moisture. Once the mist coat has dried thoroughly (usually 24 hours), you can apply two full coats of your chosen emulsion.

For kitchen environments, we recommend a durable matt or eggshell emulsion with good scrub resistance. Brands such as Little Greene, Farrow & Ball Modern Emulsion, and Dulux Trade Diamond Matt all perform well in kitchen settings where walls are exposed to grease splashes and need periodic wiping down.

Painting Structural Steelwork

Most London kitchen extensions involve at least one steel beam — usually a universal beam (UB) or a rolled steel joist (RSJ) spanning the opening where the rear wall has been removed. Some homeowners choose to box the steel in with plasterboard, but many prefer the industrial aesthetic of an exposed beam, particularly in contemporary open-plan designs.

Exposed steelwork must be properly primed before any decorative finish is applied. If the steel has been delivered with a red oxide or grey shop primer, this provides temporary protection only and is not a suitable base for a topcoat. We recommend cleaning the steel thoroughly, degreasing it, and applying a high-build zinc phosphate metal primer before finishing with two coats of a suitable paint.

For an exposed beam in a kitchen, the finish options are:

• Matt or eggshell in the wall colour — this makes the beam recede visually and works well in lower-ceilinged extensions
• Dark contrast colour — charcoal, deep navy or black gives the beam a deliberate industrial character
• Specialist metal paint — products like Hammerite Direct to Rust or Rustoleum provide a tough, wipe-clean finish in a range of sheens

Whichever finish you choose, ensure the primer and topcoat are compatible. Mixing solvent-based primers with water-based topcoats can cause adhesion problems if not done with the right products.

Bi-Fold and Sliding Door Frames

Bi-fold doors are a defining feature of the modern London kitchen extension. The frames are usually aluminium (powder-coated from the factory) or engineered timber. In most cases, the factory finish on aluminium frames does not require painting — but the timber reveals, architraves and any adjoining joinery around the door opening certainly do.

Timber frames around bi-folds are exposed to significant condensation, particularly in winter when warm moist air inside the kitchen meets the cold glass. Use a flexible, moisture-resistant paint system — an acrylic primer-undercoat followed by two coats of a durable water-based satinwood or eggshell. Avoid brittle oil-based paints on these frames, as the thermal movement of the timber will cause cracking at the joints.

Where aluminium frames meet plastered reveals, apply a clean, sharp masking line. The junction between the powder-coated frame and the painted plaster is highly visible when the doors are closed, and any paint bleed or rough edge is immediately noticeable.

Ceilings in Kitchen Extensions

Ceilings in new extensions are typically plasterboard with a skim finish, and they need the same mist coat treatment as the walls. However, kitchen ceilings also need to resist steam and condensation. A durable matt ceiling paint — such as Dulux Trade Supermatt or Little Greene Intelligent Matt Emulsion — will tolerate occasional wiping and will not yellow in the way that older vinyl matt formulations sometimes did.

If your extension has rooflights or a lantern, pay particular attention to the plasterwork immediately around them. These areas are prone to condensation and temperature differentials, and any paint adhesion failure tends to show here first.

Colour Considerations for Open-Plan Spaces

A kitchen extension typically opens into an existing dining or living area, creating a single long room. The colour scheme needs to work across the full depth of the space. In practice, this often means using a single wall colour throughout for continuity, with variation introduced through the kitchen cabinetry, the island unit, and accent details.

Light, warm neutrals remain the most popular choice across our projects in Belgravia, Chelsea, Pimlico and Fulham. Farrow & Ball's Wimborne White, Little Greene's Loft White, and similar soft whites reflect the natural light from the bi-folds without feeling clinical. Stronger colours can work beautifully on a single feature wall or on the chimney breast in the existing part of the room.

When to Call in a Professional

Painting a kitchen extension involves multiple substrates (new plaster, steel, timber, possibly existing brickwork), each requiring a different preparation and product approach. If the mist coat is skipped, or the steelwork is poorly primed, or the wrong sheen is used on a high-moisture surface, the consequences tend to emerge within the first year — and remedial work on a newly fitted kitchen is disruptive and expensive.

A professional decorator experienced with new-build finishes will ensure each surface is treated correctly, that drying times are respected, and that the finished result is durable as well as attractive. If your London kitchen extension is nearing completion, we would be happy to advise on timing and specification.