Oil Paint vs Water-Based Paint for Sash Windows: The Definitive London Guide

The Question Every London Period Property Owner Asks

If you own a Victorian or Edwardian house in London and you are thinking about repainting the sash windows, someone — a decorator, a neighbour, a well-meaning friend — will tell you that you absolutely must use oil-based paint. Someone else will tell you that oil-based paint is outdated, that water-based products are now just as good, and that modern acrylic technology has made the old arguments obsolete.

Both views contain truth and both contain oversimplification. The right answer depends on the specific window, the existing paint system, the timber condition, and — crucially — whether the building is listed. This guide explains the actual considerations, names the specific products that perform well in each context, and gives you the information to make a genuinely informed decision.

Why Oil Was Traditional: The Technical Case

Oil-based gloss paint was the default for joinery — including sash windows — for most of the twentieth century, and the reasons are rooted in the chemistry of the paint rather than tradition for its own sake.

Oil-based paint penetrates into the top layer of timber fibres as it dries, creating a mechanical bond between the paint film and the substrate. Water-based paint, by contrast, sits more on the surface. This penetration means that oil paint is more resistant to the movement of water through the timber, and it provides a seal against moisture ingress that is particularly important in exposed locations — south or west facing windows taking direct rain, or windows with damaged putty where water can get behind the glass.

Oil-based paint is also more flexible. As timber expands and contracts seasonally — and on a single-pane sash window the movement can be several millimetres over the course of a year — an oil-based film can accommodate this movement without cracking. Older acrylic paints were less flexible and more likely to crack at the edges of putty lines and in the corners of rebates, where the movement is greatest.

Finally, oil-based paint self-levels exceptionally well as it dries, flowing out to eliminate brush marks in a way that older water-based paints could not replicate. The result, applied properly, is a glass-smooth surface with a depth of finish that was simply not achievable with water-based products twenty years ago.

How Water-Based Has Changed: The Honest Assessment

The water-based paints available today are categorically different from those available in 2000 or even 2010. The introduction of alkyd-modified acrylic technology — sometimes called "waterborne alkyd" or "acrylic alkyd hybrid" — has addressed most of the historic weaknesses of water-based products for joinery.

The best modern waterborne alkyds flex with the timber, self-level almost as well as traditional oil gloss, and dry to a film that is harder and more resistant to knocks and scuffs than traditional oil paint. They also benefit from faster drying times — typically two to four hours to recoat versus eight to twelve hours for oil — and they clean up with water rather than white spirit, which matters when you are working on multiple floors of a townhouse.

The critical caveat is that quality varies enormously across products marketed as "water-based gloss." A budget water-based gloss from a DIY shed bears almost no resemblance, in terms of film quality and durability, to a properly formulated waterborne alkyd from a professional-grade manufacturer. This distinction matters more for sash windows than for almost any other painted surface, because the windows are exposed, subject to movement, and visible in strong light at close range.

The Products That Actually Perform

For oil-based paint on sash windows:

Craig & Rose 1829 Chalky Emulsion is primarily an interior product, but Craig & Rose's oil-based gloss range is among the best available for period joinery. Their formulations carry forward Victorian-era pigment chemistry in a modern oil base, producing a depth of colour and finish quality that is particularly appropriate on original Victorian sash windows.

Dulux Trade Diamond Gloss is the workhorse oil-based product for professional decorators — it applies well, levels well, and dries to a consistent, durable finish. It is not the most characterful paint, but it is reliable in conditions where reliability matters.

Little Greene Oil Eggshell is our preferred choice for interior-facing surfaces of sash windows in period properties, particularly where the colour needs to coordinate with a Little Greene wall colour. The oil-based eggshell finish is far more appropriate on Victorian joinery than gloss — the slightly lower sheen suits the scale of the detail.

For waterborne alkyd on sash windows:

Teknos Futura 40 is the product that has converted many experienced London decorators from oil to water-based for joinery. It is a waterborne alkyd that genuinely self-levels, genuinely flexes, and produces a finish that is difficult to distinguish from a well-applied oil gloss. Teknos is a Finnish manufacturer with a strong commercial reputation and distribution through specialist trade suppliers — it is not available in B&Q, which is partly why it performs as well as it does.

Zinsser PermaWhite Exterior is worth mentioning specifically for the exterior faces of sash windows, where moisture resistance is paramount. It is a waterborne product with excellent resistance to moisture and mould, and it outperforms most oil-based paints in genuinely exposed conditions.

Dulux Trade Weathershield Gloss is the accessible option for exterior-facing joinery — it is available through most trade suppliers, applies well, and has good resistance to UV degradation that matters on south-facing elevations.

Listed Buildings: What the Rules Actually Say

For properties that are listed — and there are thousands in London from Islington to Kensington — the paint specification for sash windows is not entirely a matter of personal preference or performance.

Listed building consent is required for any alteration that would affect the character of a listed building. The question of whether a paint change requires consent is genuinely complex. Repainting in the same colour with the same type of finish — oil to oil, gloss to gloss — is generally considered maintenance and does not require consent. Changing from oil-based to water-based paint, or from gloss to eggshell, or from white to cream, may constitute an alteration that affects character.

In practice, most local authority conservation officers take a pragmatic approach to paint specification on listed buildings, and many will confirm informally that a change from oil to waterborne alkyd — which produces an identical-looking finish — does not require consent. But "informally" is the operative word. If you are in any doubt, we recommend a pre-application conversation with your local authority's conservation officer before proceeding.

Historic England's guidance on painted surfaces in listed buildings emphasises the importance of breathability — particularly for lime-washed brick, limeplaster walls, and lime putty glazing in windows. For sash windows specifically, Historic England recommends using a paint system that is compatible with the existing putty chemistry. Most modern oil-based and waterborne alkyd products are compatible with linseed oil putty, which is the traditional material and the one that should be used on listed windows.

For windows where the putty has been replaced with a modern synthetic putty — sometimes done in earlier maintenance cycles — the compatibility question is less critical, but we always check the existing putty chemistry before specifying a paint system.

How to Decide: A Practical Framework

Use oil-based paint when:

• The existing paint on the window is oil-based and in reasonable condition — matching the existing system is nearly always the right approach
• The windows are on a listed building where conservation officers have specified oil-based paint
• The windows are on a particularly exposed elevation (south or west facing, exposed to prevailing rain) and moisture resistance is the primary concern
• The client is committed to a very high-sheen gloss finish and wants the maximum self-levelling performance

Use waterborne alkyd when:

• The work involves occupied properties where solvent fumes are a significant concern
• The windows require multiple coats in quick succession — the faster drying time of waterborne alkyds makes this practical
• The existing paint system is in poor condition and being stripped back, giving a clean surface to bond to
• The client wants a low-sheen eggshell finish that coordinates with water-based wall colours

In both cases, the preparation is the same — and the preparation is what matters most:

Strip back any areas where the existing paint has lost adhesion. Sand the surface to provide a key. Apply a shellac-based primer (Zinsser BIN) to any bare timber or any areas that have been filled. Use a period-appropriate undercoat — Dulux Trade Quick-Dry Undercoat for waterborne systems, Dulux Trade Undercoat for oil-based. Apply two finish coats with adequate drying time between them.

The finish coat, whether oil or water-based, can only perform as well as the preparation beneath it allows. We have seen beautifully applied Teknos Futura failing within eighteen months because the existing paint beneath it was not stable. We have also seen perfectly good oil-based gloss lasting twenty years because the preparation was done correctly and the primer system was appropriate.

The Sash Window Specific Challenges

Beyond the paint system choice, sash windows in London period properties present technical challenges that apply regardless of which paint you use.

Painting sashes in the correct sequence matters. There is a specific order in which the sashes should be painted — raising and lowering them during the process to ensure all surfaces are reached without painting the window shut. Experienced decorators know this sequence; those without sash window experience often do not.

The meeting rail — the point where the two sashes overlap in the closed position — is the area most frequently painted shut by inexperienced decorators. The meeting rail needs to be painted with the sashes in the position that allows the rail edges to dry without touching each other.

The glazing line — the seal between paint, putty, and glass — is both the most important functional detail on a sash window and the most common point of failure. The paint must slightly overlap onto the glass (typically 1-2mm) to create a seal against the putty. Decorators who cut too neatly to the glass edge leave a gap that allows water to get under the putty, eventually leading to putty failure and glass that rattles.

Our Recommendation

For the majority of sash window painting projects we carry out in London period properties, we now specify Teknos Futura 40 for external-facing surfaces and Little Greene Oil Eggshell for internal-facing surfaces, unless the building is listed and the conservation officer has expressed a preference, or unless the existing oil paint system is in sufficiently good condition to justify working with rather than against it.

This is an opinionated position, and we hold it based on the practical evidence of ten-plus years maintaining period sash windows across London. But the right product always depends on the specific window and the specific building, which is why we always inspect before we quote — and why we are happy to discuss the specification in detail with clients who want to understand the reasoning behind our choices.

For more information about our sash window painting service, or to arrange a visit and quotation, contact us through the website.