Homeowners who have installed wooden decking are familiar with the maintenance and the requirements, such as sealing their deck. The reason wood decking should be sealed is due to water absorption. Moisture and fungi play a key role in the rotting and decaying of wooden decking. Sealing the deck is one of the best ways to prolong and reduce these effects of water absorption. This protects wooden decking from moisture and increases its life span; however, sealing must be done annually to ensure you get these benefits.

Many customers ask if composite decking needs to be sealed. The short answer is “no.” Composite decking doesn’t need to be sealed as it has been produced to provide an improved alternative to wood decking. One of the key benefits of composite decking is that it does not need to be painted, sealed or stained. This write-up details why you should or shouldn’t seal your decking.


What Is a Composite Deck?

The difference between composite decking and wood decking is that one is a synthetic material produced with recycled wood and plastics, and the other is a 100% natural product sourced from trees. Composite decking is produced by heating wood and plastic using bonding agents; it is then pushed through a mould and shaped into a board. After this, the composite boards will then cool and be cut into suitable lengths. The advantage of using plastic wood decking is that it will last longer than timber decking, meaning when you install your plastic wood decking outdoors, it will stand the test of time. 

Why Homeowners Seal Their Decking

As stated above, homeowners seal their decking to prevent moisture or excess water from entering the decking board. When you install decking in your garden, it becomes susceptible to rain, snow, and moisture from the natural environment. Rain and moisture will soak into the decking boards and, if left untreated, will eventually cause issues.

This implies that when rain falls, your decking will absorb the water. The disadvantage of that is that your decking will swell and absorb the moisture making the board soft and brittle; over time, this will cause rotting and gradual decay of your decking. To prevent your wood decking from swelling and absorbing excess water and moisture, we recommend sealing your deck.

Does Composite Decking Require Sealing

As mentioned before, composite decking does not necessarily need to be sealed.

Why would you want to seal your decking?

Composite decking will still absorb water and, if left without maintenance, will attract mould and mildew. Now, this can be prevented by regularly cleaning the deck with hot soapy water and a soft brush. Another reason some customers want to seal their composite decking is to lock in the colour for longer.

Composite decking, in particular first-generation composite decking, has a wood fibre surface texture which is more susceptible to absorption. Capped composite decking has a plastic layer meaning this cannot be sealed and never needs to be. As the first generation has a wood-based surface texture, it can be sealed if you want to take extra precautions.

Composite boards in both generations will not take in excess moisture like timber decking. They will swell and expand side to side, but only by 2 to 3mm. The boards are designed and produced to outperform wood in every way, and they simply do not need to be sealed to prolong their life. Choosing to seal composite decking is optional and not imperative.  

What Kind of Sealer Should I Use?

As discussed, choosing to seal your composite decking is completely optional. We have been asked this question many times and have tested and found the best option is a hard wax-based sealant. When applied, this will enhance the colour and almost provide a wet and shiny look to your composite deck. As we are still testing applying this, the advantages of doing this are unknown, and our key goal is to understand what effect or long-lasting benefits this has on its colour and moisture absorption. In theory, sealing your composite decking should prolong its colour and provide a better rate of water absorption, which could further improve its resistance to mould and mildew.

How to Seal My Composite Decking

sealed board

Sealing your composite decking begins with removing everything you put on it. After removing what is on top of your decking, you can then proceed to clean the surface. Note that the sealing process coincides with the process of maintenance. You should seal the deck during the maintenance process once the deck is clean and clear of debris.

Clean the top of your plastic wood composite thoroughly until you have taken all dirt away. If there is an oil or grease stain, you can try scrubbing this with warm soapy water and a soft brush. After scrubbing and cleaning your WPC decking, you can rinse the top with water until you have removed all dirt from the surface.

Then, you should empty the stain or sealant into a bucket and use a roller to apply the stain on the surface of your plastic wood decking. Do this along the grain of your composite boards. When you have finished sealing your plastic wood composite, you can leave it to dry.

Once dry, you will notice the colour has enhanced in appearance, and the boards have almost a wet look to them.


Should I seal my composite decking? You don’t have to seal your composite decking to make it last longer. But if you want to, you can use a wax-based sealant; this is the sealant we used in our current and ongoing testing. The wax-based sealant enhanced the deck’s colour and overall appearance.

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