Painting Inter-War Semi-Detached Houses in London: Pebbledash, Crittall Windows and Colour Schemes

London's Inter-War Semis: A Distinct Decorating Challenge

Between the two world wars -- roughly 1919 to 1939 -- London expanded dramatically into its outer suburbs. The inter-war semi-detached house became the defining housing form of this expansion, and it is estimated that around four million were built across Britain during this period. In Greater London, they are concentrated in areas such as Raynes Park, Edgware, Hendon, Wembley, Hornchurch, Orpington, Sidcup and across much of the outer ring.

The inter-war semi is architecturally distinct from both its Edwardian predecessor and the post-war properties that followed it. It draws on a Arts and Crafts and Tudor Revival vocabulary: pebbledash render, half-timbering in the gable, casement or Crittall steel windows, concrete roof tiles or clay plain tiles, and a front bay window that is often tiled internally. This combination of materials presents specific challenges for exterior decoration that require different approaches from those used on earlier or later property types.

Pebbledash: To Paint or Not to Paint

The most significant exterior surface on most inter-war semis is pebbledash. Original 1930s pebbledash on an unpainted property is generally better left unpainted -- the aggregate is self-draining, breathable and low-maintenance. Problems arise when pebbledash has been painted previously, often because it had become stained or the homeowner wanted a colour change.

Once pebbledash has been painted, it generally needs to be repainted on a regular cycle because stripping paint back from the highly textured surface is practically very difficult. The question for most London owners of inter-war semis is therefore not whether to paint but how to maintain an existing painted pebbledash system well.

The correct product is a flexible, textured masonry coating -- not a smooth masonry paint. Smooth masonry paint applied by roller will collect in the voids between the aggregate without forming a continuous film over the surface, giving a patchy and rapidly deteriorating result. A flexible textured masonry coating such as Dulux Trade Weathershield Textured Coating, Sandtex Trade Textured Masonry or K Rend TC15 applied by roller or brush gives a continuous film over the surface, bridges fine cracks and provides much better durability.

Coverage on pebbledash is significantly lower than on smooth render -- typically 4 to 6 square metres per litre -- and the additional material cost should be factored into any quotation. On a standard inter-war semi, this product application is a significant material cost compared with smooth masonry paint.

Half-Timbering in the Gable

Many inter-war semis have half-timbering in the gable -- decorative applied timbers, usually softwood, fixed to a render or brick backing to suggest a Tudor structural frame. These timbers are almost universally painted black, and the panels between them are painted cream, white or occasionally a light colour.

The timbers require careful preparation: check for any softness, rot or failed caulk at the junction with the render panels. Any signs of rot must be treated with an appropriate wood hardener and filler before painting. The junction between timber and render should be caulked with a flexible exterior sealant before painting to prevent water tracking behind the timbers and causing rot from the rear face.

Oil-based exterior gloss in black remains the traditional and most durable choice for the timbers. Water-based black satins are available and perform adequately, but oil-based gives a harder-wearing result on a surface that sees weather exposure from multiple angles.

Crittall and Steel-Framed Windows

Crittall Windows -- the Essex company whose steel casement windows were ubiquitous in inter-war housing -- are a defining feature of the 1930s semi and are now valued both architecturally and environmentally. Original Crittall windows in sound condition are worth preserving rather than replacing.

Painting original Crittall windows is specialist work. The steel frames corrode where the paint film has failed, and the narrow profiles make preparation and painting fiddly. The correct approach is:

First, assess the condition of the steel. Where corrosion is present, it must be treated. Light surface rust can be treated with a rust converter before priming. Significant corrosion may require mechanical removal and a zinc-rich primer.

For sound, previously painted Crittall frames, wire brush any loose or flaking paint, sand to a key, spot prime any bare metal with a zinc phosphate primer and apply two coats of oil-based gloss or metal paint. Teknos Nordica Aqua is widely used by professional decorators on metal windows as a durable water-based alternative.

Colour for original Crittall windows on an inter-war semi is almost invariably white or, occasionally, black. Period-accurate Crittall frames were supplied in a range of factory colours but white became standard in most residential applications.

Replacement windows described as Crittall-style are available in aluminium, uPVC and genuine Crittall steel, and their painting requirements differ. Consult the window supplier or a professional decorator for the correct primer system for the specific frame material.

Rendering Over Pebbledash

Some owners of inter-war semis choose to re-render over the existing pebbledash to achieve a smooth, contemporary finish. This is a significant undertaking that involves either applying a thin coat of smooth render over the existing surface or, in some cases, removing the pebbledash entirely and re-rendering from scratch.

Over-rendering pebbledash is technically feasible but requires that the existing pebbledash is sound and properly bonded. If sections of pebbledash are blown or poorly adhered, they must be removed and replaced before the new render is applied. The new smooth render should be a sand-cement or polymer-based product appropriate to the substrate.

Once re-rendered, the surface requires four to six weeks to cure before painting. A stabilising primer or alkali-resisting primer is applied, followed by two coats of smooth exterior masonry paint. On an inter-war semi, this transformation from textured to smooth creates a much more contemporary appearance and significantly changes the property's visual character.

In conservation areas, changing the external appearance of an inter-war semi in this way may require planning consent. Check before committing to the work.

Colour Schemes for 1920s and 1930s London Semis

The inter-war semi is more forgiving of colour variation than Georgian or Victorian properties, and London's outer suburbs do not generally impose the same conservation restrictions as the inner city. This gives owners more freedom.

Period-appropriate choices for rendered elevations include cream, white, light stone and warm buff. The panel sections of half-timbered gables are almost always light -- white or cream -- to contrast with the dark timbers. Front doors in the 1930s were often in deep reds, greens, blues or black.

For a contemporary approach that respects the period, warm greys such as Farrow & Ball's Purbeck Stone or Elephant's Breath on the rendered panels, black on the timbers and a feature colour on the front door give an updated but coherent result.