Although the timber used for decking should have been treated to ensure longevity, black mould seems an inevitable problem. David Coton has a few suggestions on how the mould can be prevented or the timber restored.
Decking is very versatile and adaptable, an ideal way to build a recreational or relaxation area on what may be difficult sites.
But it's a fact that all timber exposed to the weather is liable to develop black mould, especially if it's in a damp area with little air circulation or lack of direct sunlight. When water gets into the wood, it forms an inviting damp habitat for mould to proliferate.
Protecting The Timber
To have the best chance of avoiding mould, only good quality timber should be used for decking. Wood used for Forest decking kits for example is kiln dried, structural grade and pressure treated, guaranteed against rot for fifteen years.
Once in place you should apply a decking protector. This will be absorbed into the wood and provide barrier against rainwater.
As an alternative, decking oils or stains will also penetrate into the timber, this time not only waterproofing but also enhancing its appearance.
One of these three types of preventative measures should be applied annually.
When mould becomes apparent, brush or scrap it off along with any other debris and apply a fungicidal wash or cleaner according to their instructions, then scrub with a stiff brush.
If you have allowed the decking to become very weatherbeaten, then use a brush or pressure washer to remove the mould and previously applied protection. Then apply restorer with a brush normal garden broom or brush, working it all over and well into the surface. You then wash the surface with a hose.
Let the surface dry for several days before adding one of the previously mentioned protectors.