Finishes for external timber

Finishes for external timber

Date Published

17 August 2022

Document Type




Member-Only Resource
Access is restricted to members (log-in here). Learn about joining or contact us for more info.


Timber that has no protective finish will often weather to an attractive appearance. However, in many situations, it is necessary to specify a protective finish. Appearance is often the main reason for specifying a finish, but other characteristics are important too.

The technology behind protective finishes moves rapidly and the range of generic types and manufacturers’ variants is bewildering. Deciding whether to specify preservative, paint, varnish or stain is just the start.

This Wood Information Sheet (WIS) outlines the need for finishes, the different types of finishes as well as the performance of the various finishing types, helping specifiers to select the correct finishing coat for the job.

Key Information

Timber exposed to weather and not protected by some kind of finish will ‘weather’ and quite rapidly become bleached and grey.

There are four basic types of materials suitable for the exterior treatment and finishing of wood: preservatives, paints, varnishes and wood stains.

BS EN 927-1 offers a framework where coatings with specific appearance criteria can be matched to end use without compromising functionality.