Cladding Finishes

In order to deliver the desired service life, any coating applied must be maintained in good condition in accordance with the manufacturer’s guidance.

The ease of access and requirement for maintenance will largely determine what product is selected.

Surface coatings work best on timbers that are dimensionally stable or have a low potential for moisture change movement. Surface texture is also important and coatings generally perform better applied to sawn rather than smooth planed timber. The process of preservative treating or modifying wood has a positive impact on coatings adhesion.

Various types of coatings are suitable for cladding ranging from clear, water repellents to translucent pigmented and solid stains and paints. Products can be applied by brush or spray on site but it is the full factory finishing of cladding with an extended maintenance system that is best for long term performance. 

With site applied coatings, TDCA recommends that at least one coat is applied to all faces including the end grain, prior to installation.  Further coats can then be applied to the visible face.

The use of moisture permeable coatings is highly recommended. These coatings have been specially developed for external timber as they are resistant to cracking, flaking and peeling associated with more brittle varnishes or paints which can trap water under their surface.

The more pigmented a coating the more the substrate is protected against discolouration and damage by the sun. Even in highly pigmented coatings, ultra violet light (UV) can affect the adhesion between the finish and the substrate causing it to separate.

Most modern coatings contain UV inhibitors. These include clear water repellents and translucent stains but the UV protection diminishes more quickly and more frequent maintenance of the surface is required.

Most naturally durable timber species, modified wood and softwoods treated with copper/organic biocide preservatives can be left unfinished to weather naturally. Many architects purposefully require the bleached, weathered look as part of the evolution of the design.

The orientation of the cladding on the building will have a material impact on the rate of weathering. Southerly and western facing walls more exposed to UV and driving rain will weather faster and be more silvery in colour than northerly or eastern facing walls which will be darker in colour and may be prone to dampness and surface moulds. Shade from a canopy, overhanging trees or nearby buildings may also have a localised impact and cause variations in colour on the same elevation. High tannin content species are more prone to this than others.