Algae (a slimy green film), moss (a fuzzy green plant) and mould (a black-green fungus) thrive in damp, shaded conditions. Unfortunately, they can multiply quickly on wood surfaces.

Not only is their appearance most unwelcome, but the moisture associated with algae, moss and mould on your deck can shorten its lifespan. Mould spores can actually be a health risk, too – and a mossy, algae-ridden deck is actually very slippery.

Keeping your deck as dry as possible, timely cleaning and potentially using a sealant will almost certainly prevent your decking from going green.

How to stop algae and mould building up on your deck

Sweep your deck

Without moisture, algae can’t grow – so try to keep your deck as dry as possible. Regularly sweeping away any pooling water and debris (such as pine needles, leaves and dirt) will allow sunlight to reach the wood and minimise moisture buildup.

Inspect for algae and mould buildup

Give your timber deck a thorough once over occasionally, taking particular care to check areas that are shaded. If you spot algae or mould spots beginning to form, clean them away as soon as you can.

Consider using a cleaning solution consisting of a small amount of dish washing soap dissolved in warm water. If the algae has taken hold particularly strongly, a 1-part white vinegar to 20 parts warm water can also provide decent results. This should be applied with a stiff bristle scrubber brush.

We wouldn’t recommend bleach – it can be toxic to waterways and might also impact the colour of your wood and the integrity of any fixings.

Seal your deck

If your deck is in a shaded area and algae, moss and mould are persistent problems, applying a water-repellent treatment will seal and shield it from most ongoing moisture-related damage.

Some products we’d recommend include Owatrol H4 Wood (a transparent oil), or Owatrol Aquadecks and Owatrol Textrol (both semi-transparent oils, available in a range of colour tints). More detail is available in our timber decking treatment how-to guide.

How to bring a green deck back to life

Firstly, clear any furniture and other miscellaneous items away. Then, using a stiff brush, sweep away debris. You may wish to cover up any nearby plants or grass with a dust sheet.

As we mentioned just earlier, a cleaning solution consisting of a small amount of dish washing soap dissolved in warm water can provide decent results. For more stubborn dirt, mix approximately 1 part white vinegar (or a small amount of dish washing soap) with 20 parts water. 

For particularly heavy duty cleaning or to remove any pre-existing treatments, there are dedicated decking cleaners and restorers available at home improvement and DIY stores. We’d recommend something like Owatrol Net-Trol or a diluted solution of Owatrol Prepdeck. 

The solution should be poured directly onto the decking and scrubbed with a long-handled bristle scrubbing brush – the bristles should be strong, but should not damage the wood fibres. Once the entire deck has been scrubbed, leave for approximately 15 minutes.

Then, rinse. Pressure washers on a low setting can be great for removing any lingering algae or mould – work from one end to the other of each board. Avoid high pressure settings and keep moving to avoid damaging the wood. If you don’t have a pressure washer, then scrubbing with a stiff brush and hosing down works equally well.

If you’re applying any further treatments, then wait for the deck to dry completely (or risk coating failure!). Again, be sure to check out our how-to guide to timber decking restoration.

Upgrading your outdoor space?

We supply a range of solid wood timber decking, fencing and cladding.

All of our products are available in a range of high-performance species – sustainably imported from across the world – and machined to your specification by us. They can also be pre-treated prior to delivery, to ensure exceptional outdoor performance.

Use the button below (or message us through our contact page) to start your project.