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Monday, March 8, 2010

Deck Maintenance / Mould and Mildew

This is one of the most common topics I am asked about. There is a lot of controversy over so called maintenance free decking...... Hopefully I can clear this up. There is no such thing as "maintenance free decking". However, there are materials that require less maintenance than others.

Wood Decks

Most people are familiar with traditional wood decks such as Pressure Treated and Cedar. I remember back in the early 1980's when the cost of cedar was really not much more than the cost of pressure treated lumber. However people were choosing to build with pressure treated lumber because they thought it was some kind of miracle wood that never had to be painted, stained or sealed. Clients were choosing this with a misunderstanding of what the pressure treating chemical actually did. The chemical was and is only used to help prevent the rot and decay of the lumber. The chemical does nothing to prevent the cupping, twisting, splitting and splintering of the wood. So to help prevent this damage it is necessary to maintain your deck with a stain/sealer. It is also recommended to use a stain/sealer to act as a barrier between your skin and the chemical in the wood.

Cedar on the other hand has natural resins within the wood that help to control the rate that moisture is absorbed and released from the wood. This natural control of moisture helps to reduce the amount of splitting, cupping and splintering in cedar. It is recommended to stain/seal cedar to help maintain its beauty and also to control damage to the wood.Beyond staining and sealing your deck I also recommend regularly washing your deck to help prevent mould and mildew from forming on your decking.

This is where the controversy begins. We are now seeing a wide variety of different materials to choose from for building a deck with. A large percentage of the marketplace is moving towards lower maintenance products. It reminds me a lot of the story I mentioned above regarding pressure treated being a miracle wood. Today many people are becoming frustrated seeing their high-end, low maintenance deck get mouldy. There is a misunderstanding of the materials and their limitations. Basically any material outdoors can and usually will get mould on it if it is not cleaned regularly. I commonly see mould on patio furniture, window sills, deck floors (wood and composite) stone patio's, fences, sheds, concrete etc...

The photo on the right shows the top of a concrete retaining wall that is badly stained with mould. This just shows that mould can and will grow on anything. The presence of organic materials such as wood fiber are not always necessary for mould growth. Once the presence of mould is found, it should be cleaned with the appropriate recommended cleaner.

Black Mould on a Pressure Treated Deck
The photo (above the concrete retaining wall) of the cedar fence has quite a bit of mould starting to form on the cedar. The mould initially shows up as spotting but is fairly quickly absorbed into the wood to become a consistent stain of black mould covering the surface of the deck. You can see this wood deck (to the right) that is just black with mould.

Composite Decks
The main difference between wood and composite decks is that the mould staining on composite decks does not penetrate into the material like it does with natural wood such as cedar. The mould grabs onto the exposed wood fiber in the composite decking and shows up as the same spotting that we see on wood decks . However it does not penetrate any deeper due to the layering and encapsulation of the plastics in the composite decking. Is it unsightly? Yes. Can it be cleaned off? Yes. Generally a deck wash recommended by the manufacturer of the composite decking will remove the staining. Usually a deck around 250 sq ft can be cleaned in about an hour or so. There is very little scrubbing involved with most deck washes. They are usually applied with a pump sprayer then rinsed off with a hose and water. With wood decks the sanding and prep work prior to actually staining your deck is a huge time commitment. So although there is still maintenance involved with a composite deck it is considerably less overall. The disadvantage to cleaning your deck is that it will generally lighten the appearance of the material. So if you have a dark composite deck you can expect that to become lighter after cleaning. I would recommend spot testing your cleaner to make sure you are going to be happy with the results.

Some of the newer products on the market today such as Timbertech XLM, Trex Trancends and Fiberon offer some great benefits. Trex Trancends has a 25 year warranty against fading and staining, Fiberon also offers a 20 year warranty against fade and stain on a few of its products. All three of these products have a protective layer on the surface of the planks. This protective layer has no organic fiber exposed so the chance of mould growth is greatly reduced. Also the cap layer on these products has excellent performance against scratching, denting, scuffing and they are very easy to clean. Most cleanups of these products would just involve soap and water.

I have only touched on a few of the many different products available today. There are pros and cons to each and every material. At the end of the day you need to choose what is going to be best for you and your family's lifestyle. Each and every deck will require some degree of maintenance. Some materials may offer a greater scratch resistance but look more artificial. Some materials may look more natural but offer less protection against mould and mildew. Take your time and speak to professionals such as myself that have experience with the different products on the market. If you have any questions or topics you would like me to discuss further feel free to contact me and let me know.

Thanks for your time

Todd Mounsey

Owner / Designer