Trade Tips: Changing from Light to Dark Colours on Exterior Doors

Here on The Chromologistpainting front doors is one of our favourite subjects. It’s a project that delivers high impact with comparatively low amounts of time and effort, can be completed in all manner of colour and style variations, and gives any property an instant facelift.

But if there’s one unexpected thing that could derail your front door project, it’s the potential side effects of a dramatic colour change. “Changing the shade of exterior woodwork from light to dark will greatly increase the amount of heat the surface is able to absorb from the sun,” says our in-house technical expert, Wayne Armstrong.

“In some cases, this additional heat may cause resin and gases to be released by the wood, particularly from any knots. This can result in peeling and blistering, which may not have occurred when painting the same surface with a lighter shade.”

To minimise the risk of this happening, and to achieve a long-lasting finish, Wayne has a few tried-and-tested tips to offer. “We recommend removing as much of the previous coating as possible to expose and prepare any knots before treating with our Wood Knot & Resin Blocking Primer.

“This should be followed with a coat of Farrow & Ball Exterior Wood Primer & Undercoat in the recommended tone for your new paint colour, followed by two coats of your chosen top coat.

“As professional tradespeople, we often consider additional information while striving to follow best practice,” he continues. “With this in mind, we include a section of guidance from the British Standards BS6150 Painting of buildings which adds some very useful points”:

Note 1

“The potential for extractives to cause problems should be considered during the preparation of wood for coating.

Extractives confer desirable properties such as durability and colour to wood, and are manifested both as resins and in the form of soluble staining chemicals such as tannin which can disrupt or discolour surface coatings.

Knots often contain a disproportionally high percentage of resin and extractives, which can cause localised discoloration and physical disruption of paint. These problems should be alleviated through the application of a knotting solution or use of a purpose-designed stain-blocking primer.

Some woods contain a high resin content and can give rise to exudation problems. High levels of tannins can also cause discoloration. These woods should be washed down with methylated spirits immediately before priming or varnishing.”

Photos: @cakeatthecottage and @jpslifeandloves

Note 2

“However, these woods can usually be painted satisfactorily if an aluminium primer or stain blocking primer is used. Some species of hardwood and softwood contain a relatively high level of tannins distributed throughout the wood.

When finishing using a water-borne paint, a primer possessing stain-blocking properties should be used. Wood species containing high levels of tannins react with iron to produce strong blue-black discolouration. Non-ferrous fixings should be used, and steel wool should not be used for high tannin woods.

Moisture content: Wood with a low level of moisture movement should be selected as this will improve the coating's durability. An electrical moisture meter with long probes should be used so that readings can be taken at a depth not so readily affected by surface drying. Wood should be painted or varnished when its moisture content matches that of the substrate.”

Photos: @hannahharrietdotcom and @ivy_cottage_country_living