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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.
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 stain fungi to grow and 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 been 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).
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.
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 – this can also lead to the wood 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
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. For further information about a particular species, please go to the product pages or speak to our technical team.
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.
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