Even though composite decking is advertised as being very low maintenance, it is important that you properly clean and seal it to prevent unwanted growths (such as mildew). This is because composite products are actually comprised of a combination of plastic and timber fibre/flour. The wood flour is a food source for mildew to grow on. Without some sort of mildewcide to prevent it, mildew can flourish during times of high temperatures and moisture.
Cleaning & Removing Mildew
The very first thing that you need to do is clean the decking and remove any mildew, dirt or stains that have developed. It is strongly recommended that you use a power washer (instead of the garden hose and a scrubbing brush), as it will help you to get the surface much cleaner than is possible by hand and it will make the whole process faster.
It is recommended that you steer clear of bleach – whilst it kills mildew spores, it doesn’t necessarily remove them from the composite decking plus it kills plants and other vegetation. Instead, it is recommended that you use a specially designed cleaner that is environmentally safe and highly effective. It will not only kill the spores, it will remove them from the surface.
Sealing
Whilst you don’t have to seal the surface once its been cleaned, it’s strongly suggested that you do. Choosing not to seal the decking often results in needing to clean it every year or so. By properly sealing or staining the boards, you can get several years of use out of them before they need to be cleaned again. It is important that you choose the right sealer or stain.
There are several things you should look for when selecting a product. Firstly, you want a water-based one as opposed to a solvent (they are easier to work with and won’t alter the colour of the decking). Secondly, you want a product that contains zinc nano particles if possible (as zinc is a natural combatant of mold growth and will delay the regrowth of mildew).
Brushing
Regardless of how you apply the sealer or stain (rolling or spraying), it must be brushed. If you rolled it on, simply back brush it whilst it’s still wet. The same goes for spraying it on. But why is this so important? When you brush the sealer, it creates friction on the composite decking, breaks the surface tension of the wood and works the product into the pores.
Removing Excess
If you have applied too much sealer or stain, it’s important that you remove the excess. There are a number of reasons for this. Firstly, it’s for the aesthetics of the decking. When you apply too much product, it puddles on the surface and dries, leaving unsightly shiny spots. Secondly, these spots are likely to flake and peel over time (which is equally ugly).
Once you’ve finished cleaning and sealing your composite decking, it’s important that you give it time to cure. Don’t replace your outdoor furniture and keep your pets inside whilst it dries. You’ll be able to put everything back in its place the following day. Now, all you will need to do is maintain the decking timber. At the first sign of mildew growth returning, give the surface a good wash with an appropriate cleaner and scrubbing brush, hose it off and let it dry.