Before we answer this question, keep in mind that composite decking boards are made of composite lumber which contains wood fiber, plastic and binding agents. Composite decking does not require much maintenance compared to traditional wooden decking. That said, it is not necessary to seal composite decking; however, sealing will make periodic cleaning less necessary. Here are the steps to seal your composite decking:

Clean the Composite Decking

The first thing that you need to do is to clean the composite decking boards to get rid of any dirt, stains or mildew that are present on the deck. Some recommend that you use a power washer because using one will make cleaning more efficient and thorough as compared to scrubbing by hand. Just be careful since a high-pressure setting may damage the top layer of the composite decking. Also, keep in mind that once the composite decking is sealed, any dirt left behind will be “sealed” into the decking. For this reason, you must make sure that the composite decking is thoroughly cleaned. Let the composite decking cleaner sit before rinsing thoroughly. Afterwards, let your composite decking dry completely before you apply a sealer. Make sure to choose the right cleaning agent. Most would suggest the use of chlorine bleach, but this is a terrible idea. Bleach is proven to be effective at killing bacteria, viruses and mould on non-porous surfaces. However, composite decking has a porous surface, and it will prevent the chlorine bleach from penetrating the surface to reach any mould growing underneath. To make matters worse, chlorine bleach is corrosive. Continuous use of this product on your composite decking will cause premature fading, chipping, cracking and splintering of your decking boards. Aside from possibly corroding the metal fasteners that hold the boards together, bleach can also damage surrounding plants and vegetation—it will be a nightmare if the chemical compound spilled in your garden. Instead of chlorine bleach, it would be better to use a nature-friendly composite deck cleaner. There are several highly rated, environmentally safe products that are specifically formulated for cleaning composite decking and effectively removing both surface and hidden dirt, mould and mildew.

Choose What Composite Decking Sealer to Use

After cleaning the composite decking, the next step is to start the sealing process. Choosing the best possible composite deck sealer is crucial in making sure that you will be satisfied with your project once it’s complete. Water-based sealers are preferable compared to solvent-based ones. Water-based sealers have two primary advantages: 1) They do not alter the color of the composite decking boards unlike solvent-based products, and 2) They utilise synthetic resins which cannot be used as a food source for algae, mould and mildew.

Tip: Always Read the Instructions

Before you start the sealing process, it is important to make sure that you read and follow the directions on how to properly use both the composite decking cleaner and sealer. Essential information can be seen at the back of the tin, such as drying time, number of coats to apply, time allotted between coats and other critical information.

Apply the Sealer

You can apply the sealer by rolling or spraying, but always remember to back-brush. If you use a roller, back-brush the sealer in right after rolling it on while it’s still wet. If you choose to spray the sealer on, just use a roller to accomplish the back-brushing. You need to back-brush because doing so breaks the surface tension of the wood and it works the sealer into the pores of the boards. The more sealer the wood absorbs, the longer the coat will last. It is also important that you only apply as much sealer as the composite decking can easily absorb. Wipe off any excess product if you applied more sealer than what the composite material can absorb. If you apply too much composite decking sealer without wiping off the excess, the sealer will puddle on the surface and dry, leaving shiny spots on your composite decking and making it look tacky. Furthermore, these spots will tend to flake and peel.

Leave It to Cure

Once you are done applying the composite decking sealer, having followed all the steps and the instructions on the tins, your project should be looking great. Do not mess it up now by not giving your composite decking enough time to dry. Tidy up, leave your project alone for a while and come back the next day. Letting the sealer dry and cure on its own is necessary. It will be worth the wait.

Maintain the Composite Decking

Some people say that composite decking is maintenance-free, but this is untrue. Even when your composite decking is properly sealed, it still needs to be maintained. Composite decking requires low maintenance especially when sealed properly. If you see any signs of mould or mildew returning, you simply wash the surface of the deck with a composite deckinhg cleaner and a scrub brush, hose it off, then let it dry. Once done, just apply a single coat of clear sealer as a maintenance coat. It is that simple. With proper maintenance, your composite decking can last 25 to 30 years.