Painting a Kitchen Extension in London: Bifold Doors, Concrete & Continuity

Painting a Kitchen Extension in London: Bifold Doors, Concrete & Continuity

The rear kitchen extension has become the defining home improvement project for Victorian and Edwardian terraced houses across London. From Pimlico to Chelsea, the pattern is consistent: ground floor extended into the garden to create an open-plan kitchen-dining-living space with bifold or sliding doors across the back, often with a roof light above. The result is a contemporary living space grafted onto a Victorian or Edwardian shell.

Painting these spaces is more complex than it might appear. The extension introduces materials that do not exist in the original house — concrete blockwork, steel, rendered masonry, polished concrete floors — alongside the challenge of creating visual continuity between the old and the new. Getting this right requires understanding each substrate, its specific preparation requirements, and the colour and visual logic that will make the two parts of the house read as a coherent whole.

The Challenge of Visual Continuity

The first question in any kitchen extension painting project is whether continuity between the original house and the extension is the goal, or whether the design intention is to let the extension read as a distinct, contemporary insertion.

Both approaches can work well. Continuity — using the same or closely related colours throughout, from the hallway through the original rooms and into the extension — creates a sense of flowing space that makes the whole ground floor feel larger and more coherent.

Contrast — using a deliberately different palette in the extension, often something more contemporary and material-focused (raw concrete, natural plaster, pale white-lime finishes) in contrast to the period character of the original rooms — can celebrate the distinction between old and new in a way that architects and interior designers often prefer.

The decision usually comes down to the design of the extension itself. A glazed, highly contemporary structure with steel frames and polished concrete floors is better celebrated as different rather than forced into a period palette. A more contextual extension in brick or render with timber windows will absorb a period palette more naturally.

Bifold and Sliding Door Frame Painting

Steel and Aluminium Frames

Most contemporary bifold and sliding door systems are aluminium-framed, often finished in powder coat from the manufacturer. These frames cannot be painted with standard emulsion or oil paint — the non-porous, potentially oily surface of the aluminium requires specific preparation.

The correct preparation for unpainted aluminium involves degreasing thoroughly with a panel wipe or equivalent solvent cleaner, abrading the surface to provide a mechanical key, and applying a specialist etch primer designed for non-ferrous metals. Without this primer, any subsequent paint will have no adhesion and will peel off within weeks.

Steel bifold frames — used in more bespoke, high-end extension projects — require similar preparation: degreasing, priming with a zinc phosphate or direct-to-metal primer, and painting with a two-pack epoxy or polyurethane topcoat for maximum durability. These systems are significantly more durable than single-pack paints and are the appropriate specification for steel frames in external or semi-external locations.

Matching Manufacturer Finishes

In many projects, the goal is to paint the internal face of the door frame to match the interior colour scheme while the external face retains its factory finish. This requires care at the transition point — a sharp, clean line at the boundary between painted and factory-finished surfaces. Masking along the sightline of the door in the closed position is the professional approach.

Colour-matching an existing manufacturer powder coat finish is not always straightforward. The standard BS or RAL colour references used by most manufacturers can be matched in liquid paint, but the finish (matte, satin, gloss) and the substrate will affect the final appearance. Always order paint samples before committing to a full repaint.

Render and Masonry Painting

Modern extensions are typically built in concrete blockwork with an external render — either a sand-cement render or, increasingly, through-coloured polymer renders that do not require painting. Where render does require painting, the approach depends on the type of render and its condition.

New sand-cement render must be fully cured and dry before painting — typically a minimum of four weeks from application, longer in cold or damp conditions. New render has a high pH which can cause saponification (a soapy, sticky reaction) in conventional paint. Masonry paints with alkali-resistant formulas, or an alkali-resisting primer applied first, prevent this.

Existing render in good condition can be repainted with a standard masonry paint after washing down to remove any algae, lichen, or loose material. A coat of stabilising solution on any powdery or friable areas before the topcoats is advisable.

Through-coloured polymer renders (such as K-Rend or Parex) should not normally be painted — the through-colouring is part of the render system. If recolouring is needed, use a breathable silicone masonry paint from the same manufacturer's system, following their specific application guidance.

Concrete Blockwork Interior Walls

Some contemporary extensions leave internal concrete blockwork exposed as a design feature rather than plastering it. Where this is the case and some colour treatment is desired, the options include:

Masonry paint direct to blockwork — functional but will emphasise the block coursing and texture. Two coats of a breathable masonry paint, with a diluted stabilising coat first on new blockwork, will produce a flat, opaque finish.

Lime plaster skim — a thin finishing coat of lime plaster gives the blockwork a smoother surface while retaining the breathable, natural character that is appropriate for a well-designed contemporary interior. This can then be painted with limewash or breathable emulsion for a high-quality, textured finish.

Venetian plaster or tadelakt — for high-end contemporary interiors, a polished plaster finish applied over the blockwork creates a seamless, mineral surface that requires no further paint treatment and works particularly well in open-plan spaces.

Polished Concrete and Screed Floors

Concrete and screed floors in kitchen extensions are increasingly common — both polished poured concrete and self-levelling floor screeds used as a finished floor surface. These floors typically do not require paint, but they do require sealing, and the type of sealer significantly affects the final appearance.

Penetrating sealer (silane or siloxane-based) provides protection without altering the appearance — the concrete looks natural and matte. This is the preferred option for polished concrete where the natural, industrial aesthetic is part of the design intention.

Topical sealer or floor wax provides a harder-wearing surface layer and can be specified in matte, satin, or gloss finishes. Satin or semi-gloss sealers increase the depth of colour in the concrete and are a popular choice where the floor needs to stand up to very heavy use.

Floor paint on concrete is appropriate where the concrete is not polished and a durable coloured surface is needed. Two-pack epoxy floor paints provide excellent durability and are available in a wide range of colours. They are less suitable where the natural concrete aesthetic is valued.

Matching Paint to Existing Interior

When extending from the original house into the new extension using the same colour, the challenge is that the two spaces have different substrates — plaster in the original house, likely a different plaster or board in the extension — and potentially different light conditions. The colour may appear slightly different on the two surfaces even if the paint product is identical, because of the difference in surface texture and absorption.

The solution is to ensure both surfaces are prepared to the same standard before painting — both fully primed, both with the same number of undercoats — so the topcoat behaves consistently. In practice, new plaster or plasterboard in the extension will need a mist coat (diluted emulsion) to seal the surface before the topcoats, whereas the existing walls in the original house need only cleaning and sanding.

Where a colour match is critical — in a fully open-plan space where old and new walls are in direct visual contact — always use the same batch of paint and test a section before committing to the full application.

Colour Bridging Strategies

For projects where a visual distinction between old and new is acceptable, colour bridging — using a transitional palette that draws elements from both the period interior and the contemporary extension — can be very effective.

One approach is to use the same colour on the wall that connects old and new — the wall between the original rear reception room and the extension — painting it in the colour of the extension rather than the original room. This draws the eye towards the new space and creates a sense of depth when viewed from the front of the house.

Another approach is to use the same woodwork colour throughout — doors, window frames, and skirting in a consistent tone — even if the wall colours differ between old and new. Woodwork continuity provides visual coherence without requiring identical wall colours.

Our interior painting and exterior painting services cover the full range of substrates and products involved in kitchen extension projects, and we are experienced in the specific challenges of new-build-on-old-house situations.