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When Russwood timber cladding is uncoated, it will weather over time to a beautiful shade of silver-grey, providing a subtle, natural look which blends in to the natural environment.

All external building materials change over time, and wood is no exception. As it is a highly durable building material, cladding boards are expected to last for over 50 years but, during this time, the wood will age or, as it is known in the industry, weather. This weathering process will change the surface appearance of the boards and, potentially, the overall look of the building.

All uncoated timber, irrespective of species, will eventually weather when exposed to its natural environment. As long as this is understood by architects, builders and clients, it can be considered as part of the overall project rationale.

Weathering process

When timber is exposed outdoors without a protective coating the surface undergoes rapid changes to both its appearance and its texture, as a result of exposure to both sunlight and moisture.

The first observable effect is often a temporary brown staining, as extracts in the timber rise to the surface where they oxidise. Sunlight then photo-degrades the wood surface and, along with moisture enables the timber surface to grey. The shade of grey will vary according to the duration and intensity of wetting. In parallel with this, the surface of the timber will roughen, with some check marks likely to appear. These effects, which are the result of sunlight, water, mechanical forces and heat, characterise the process of weathering.

It is important to note that weathering is a normal and healthy process in timber, and should not be confused with the fungal decay, which can sometimes be observed in timber cladding which has not been graded, has been poorly specified or incorrectly installed. Fungal decay is the result of extended periods of wetting, which have allowed fungi to break down the timber.

Timber, when correctly detailed, will weather beautifully, with its appearance varying dependent on the quantity of moisture on the surface (when it is wet, the timber will appear darker in colour.

SILA Select® cladding in RW006 profile | Royal Veterinary College | NORR Consultants Ltd
SILA Select® Cladding in RW006 profile | Royal Veterinary College | NORR Consultants Ltd
SILA A/B® Cladding planed to RW009 profile - private house at Tigh Port na Long, Skye | Dualchas Architects
SILA Select® Cladding planed to RW009 profile

Building location

In areas of high rainfall some timber cladding installations can turn grey in just a few months, whilst in drier areas the process is likely to be slower. Similarly, south-west facing walls weather relatively fast, due to their exposure to sunlight, whereas north facing walls tend to weather more slowly, but uniformly.

Building design

The design of a building also determines how it will weather, as the form and shape influences the impact that wind-driven rain will have on it. For example, buildings without eaves tend to get wettest at the top, particularly at the outer corners, so this may result in these areas weathering more quickly than other parts of the wall. If there are eaves then uneven weathering can occur (unless the eaves shelter the entire wall) as sunlight will be unable to reach the areas under these eaves.

There may also be areas which, due to the design of the building, are subject to splashing during and shortly after rainfall– this can also lead to the timber weathering faster in these areas.

Over time, the entire building (unless completely sheltered from the elements) will weather to the same colour, and will remain the same silver-grey colour for years to come.

SILA Select® Cladding skimmed boards - used in Board on board layout (125 & 100mm) and fixed with L-GoFix® screws | John Puttick Associates
SILA Select® Cladding skimmed boards – used in Board on board layout (125 & 100mm) and fixed with L-GoFix® screws | John Puttick Associates

Factory Coated Accoya® Cladding | Threesixty Architecture | Nigel Rigden Photography
Accoya® Cladding 47×25 and 73×50 (on edge) factory coated with Teknos® FI-024

Timber species

As all Russwood cladding species are naturally durable, they can all be left to weather and will end up as a consistent shade of grey (unless the orientation or design of the façade prevents this). The only exception to this is Accoya® wood; which we would recommend factory coating in all instances. Different species will weather at different rates, and result in slightly different shades, dependent on their durability and density properties.

Prevention of weathering

Timber weathering is often viewed as a very attractive characteristic of timber cladding as it demonstrates that the product is natural and, over time, the silver-grey shade will allow the building to blend into its environment.

The only way to avoid weathering is to apply a clear or coloured coating to the timber, which will require to be re-applied every few years over the life of the timber. Clear coatings will preserve the original colour of the timber, whilst coloured coatings can be applied in a colour of your choosing.

Accoya® RW119 secret fix (192mm wide), factory coated in Teknos® paint
Accoya® RW119 secret fix (192mm wide), factory coated in Teknos® paint
Scotlarch® cladding factory coated in SiOO:X
Scotlarch® cladding factory coated in SiOO:X | Helen Lucas Architects

SiOO:X accelerated weathering

Most timber species can be factory coated in SiOO:X, a breakthrough silicone technology, to provide a genuine silver lustre. In effect, SiOO:X creates a weathered appearance at an accelerated rate.