Why clean your deck? We invest a lot of money and effort in building beautiful outdoor decking areas but they tend to get neglected. Your deck is like any room in your house but it is exposed to the elements. Sun, rain and dirt blowing onto the boards can create unsightly ugly decks. Your deck is made of weather resistant material but over time it will deteriorate unless it is properly cared for.
Maintaining Your Deck
Basic maintenance
Sweeping your deck is the most basic step you can take. Keeping it free from leaves and twigs will make a big difference long term, not only to its appearance but also to its potential performance. Leaves and twigs can contain tannins which can stain your decking. Piles of leaves can retain moisture and lead to mould or even rot in extreme cases. Use a stiff broom to regularly sweep your deck and try to remove any leaves that are stuck between your deck boards. The more regularly you sweep the easier it will be to maintain your deck.
Intermediate care
Along with regularly sweeping your deck, at least once a year it’s important to give it a thorough clean. In the same way that you regularly mop the floors around your house, you should do the same for your deck. Using just soap and water, give your deck a good scrub and it will make a big difference to the appearance.
Full treatment
Sweep your deck with a stiff broom, give it a wash with soapy water and then treat it with a long acting surfactant. There are a variety of products available and most commercially manufactured products will work to varying degrees. Keep in mind that the effectiveness of any of these products will depend on the environment it is used in. Lots of rain and sun will probably mean your protection will wear out faster. The main thing to remember is if you see something unsightly on your deck, clean it! The longer you leave it the harder it will be to remove later.
Your deck has mould
In most cases mould will appear as spots to begin with and then grow into patches. It will most commonly appear in exposed areas rather than under eves where the rain does not get onto the decking. Shaded areas that might stay damp longer than areas with full exposure to the sun are more likely to suffer from mould. It can appear on any surface given the right conditions; all it needs is a bit of water and warmth and then will quickly establish on your deck. Timber decking is unlike most areas around the house because it sits flat and often gets full exposure to the sun. It is quite likely that at some point a deck will suffer from some mould.
Before treating your deck for mould it is worth testing a patch to ensure you are trying to treat the right problem. Use a little Sodium Hypochlorite (bleach) to test for mould – put a few drops onto a badly affected area and see if the black or green mould disappears. If the bleach test works you can be pretty confident you are dealing with an organic mould or similar.
Decide if you need an instant result or if you’re prepared to take some time to clean away the mould. We recommend a slower approach because the chemicals used in the longer lasting slower acting cleaners are gentler on timber. Use a deck cleaner or other spray on and leave products for outdoor mould treatment. Follow the manufacturers instructions and be patient; re-application might be required for severe mould build-up.
If you need to have an instant result then you can use a bleach based product to get faster results. Commercially available outdoor mould and mildew cleaners will most likely contain an certain level of Sodium Hypochlorite so follow the instructions and don’t be tempted to leave chemicals on too long. Bleach based products will have some affect on wood fibres so the faster you can get them on and off, the better. After applying cleaners use a broom to help break away bad build-ups and allow chemicals to act on the mould.
Your deck has black rings from deck furniture or barbeque
We tend to put a lot of stuff on our decks and sometimes these objects lead to unsightly marks. The most common is a deck chair or barbeque leaving a rusty or black ring on your deck.
What has happened is the metal in contact with decking has oxidized or rusted and left a mark. To test for oxidation get a small amount of Oxalic Acid and apply to the stain. If you have red or black rust on your deck Oxalic Acid will almost instantly reduce the appearance of the mark.
Oxalic Acid is normally sold in a crystalline solid that can be dissolved in water and sprayed onto surfaces. Spraying Oxalic Acid directly onto your stains will remove the stains but it can also leave a lighter patch where the Oxalic Acid has bleached the timber. If you are going to treat your deck with Oxalic Acid then it is better to apply it to the entire area and just repeatedly spray the areas most badly affected by oxidation. Oxalic Acid also acts as a mild bleach and can help in cleaning away marks left by plant pots and other objects left sitting on the deck.
Deck chairs and plant pots are not the only things that can cause black oxidation on decking. Decks can be affected by environmental pollution and other activities. If you cut any metal near decking the iron fillings can rust on your deck and appear like mould but in fact it is a rust issue. Tin roofs can leach iron into rain water if it splashes over the guttering onto decking. Decks near industrial activity can suffer from air pollution raining down and leaving iron pollutants on the timber.
It is quite important to test what you are dealing with before trying to clean your deck. What can appear to be mould will not be cleaned away by anti-mould cleaners if it is iron oxidation. Be aware of this if you have had your roof washed, your house cleaned or had building activity around your deck.
Your deck has rubber scuff marks
This is not quite as common as mould and oxidation but some decks can end up with scuff marks from black gumboots or shoes. First try soapy water and a brush as what you are trying to get rid of is the rubber left clinging to the surface of the deck. If scrubbing with a broom does not work you may need to use a smaller stiffer brush and scrub the affected area longer. If you are really determined to reduce the appearance of boot marks then a fluffy tennis ball rubbed over the affected area is probably the best method to deal with rubber on decks.
Outdoor cleaning chemicals will not do much to help this problem. Elbow grease and a bit of determination will!
Your deck might have both oxidation and mould
If you think your deck has rust/oxidation and mould then you need to test for both and perhaps treat both in one cleaning. Use Oxalic Acid first followed by an anti-mould treatment.
The reason why you should treat the deck with Oxalic Acid first is it will help with the anti-mould treatment you do afterwards. Oxalic acid is, as its name suggests, a mild acid – the application of this acid will break down some of the mould and help clean away dirt to let the anti-mould chemicals to attack the mould more effectively.
Most cleaning product manufacturers will recommend applying products to dry surfaces. This is the most effective method of using these products. However, if you apply the products in this method, most will leave a patchy appearance because you have applied the spray unevenly. Most recommend keeping surfaces wet and this does reduce the patchy appearance but unless you are prepared to use a lot of chemicals you cannot keep bigger decks completely saturated with cleaners.
The most effective work around is to wet the entire deck first and mix your chemicals a little stronger than recommended. Get someone to help you, while one person keeps the decking area wet with a fine spray from a hose the other can spray on the cleaner. Continue this process if it appears to be drying out too fast. Sweeping will help spread the chemicals around evenly and help clean away dirt and mould.
Do not try and clean your deck at the peak of summer on a hot day. Doing it in the morning when it is cooler will make your cleaning more effective and even.