Articles: Restoring the look of discoloured and stained timber cladding

TRADA, The Timber Research and Development Association, have carried out studies into the causes of external cladding discolouration and the best ways to treat it.

Black discolouration was found to be caused by a yeast fungus, Aureobasidium, which grows on both new and old timber and is found to be more prevalent in areas exposed to direct sunlight.

Extractive staining, also known as tannin staining or watermarking, is caused by the movement of water-soluble organic compounds in the wood that occurs due to regular changes in moisture and general conditions that the cladding is exposed to.

Both the black discolouration and watermarking were found to be effectively removed by simply using a standard pressure washer, the same type you might use to clean your car.

To protect the cladding after cleaning, their tests found that applying a resin-based decking protection product kept surface discolouration at bay for more than two years, whereas untreated cladding had the mould growth return within twelve months.