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Can You Put a Sealer on Composite Decking

Composite decking does not require sealing, as timber decking does, as it is naturally resistant to moisture (not moisture-proof). However, some consumers still choose to seal their composite decking to further protect it from the elements and increase its lifespan even further.

Decking sealing is the process of applying a protective coating to a deck’s surface to enhance the material’s resistance to mother nature’s harsh elements, sealants are primarily used for the protection against moisture. This is a process that is required for timber decking to prevent mould and rot from damaging the boards. You are probably wondering; do I need to do this for composite decking as well?

Generally speaking, composite decking is manufactured to be a low-maintenance building material that does not require staining, sealing or painting. Despite this, there are still some homeowners who consider sealing their composite decking – but why?

First Generation VS Second Generation

To understand why someone may seal their composite decking, we must first look at the different types of composites. There are two main designs of composite decking and 95% of the products you see online will fall into one of these two categories. Composite decking (first generation) is made with recycled plastics and wood fibres, there is also a capped (second generation) composite decking that provides more resistance to moisture. Given that first-generation boards have a wood-fibre surface layer they are more susceptible to moisture absorption that can cause further problems down the line. Despite this, first-generation composite decking boards still absorb much less water than timber decking meaning the process of sealing is not imperative.

Due to this, some people may still consider applying a sealant to their first-generation composite decking. Given that the second generation has a protective capping, the sealant can’t be absorbed making the whole process pointless.

So if you do choose to seal your composite decking this should only be done on a first generation (uncapped composite board). If you do seal your uncapped composite decking you may be thinking what are the advantages and disadvantages to this below we take a look.

Advantages of Applying Sealers

There are many advantages to sealing your deck. One of the best reasons to apply a sealant to your composite decking is to make it easier to maintain. You can also avoid several problems, such as moisture damage and mould growth. Some varieties of seals also protect the decking from fading.

Another reason to put sealer on composite decking is to restore or brighten the colour of the decking. While it does take some time for the colour to fade from constant exposure to the sun’s UV rays, a coating of colour restoration and sealants can make your composite decking look new again.

Below are a list of the advantages to sealing your decking:

  1. · Ease of cleaning: Decks that are sealed are easier to clean and maintain given that the sealed surface resists the absorption of dirt and stains.
  2. · UV Protection: Sealing will provide additional protection against UV rays which results in colour fading, Please check before purchasing as not all sealants have UV protection.
  3. · Moisture Protection: Sealing decking helps create a shield against water and moisture. For timber decks, this is essential to reduce the amount of rotting and decay that can occur over time.

Sealants are primarily clear and used to protect your deck from moisture damage. They apply a protective layer that helps reduce water absorption, most sealants in which are clear, don’t offer UV protection and additional stain resistant benefits, so before purchasing read the label or check to confirm, please note most solvent-based decking oil protect against UV rays and offer up some stain resistant benefits.

Disadvantages of Applying Sealers

While there are more than a few reasons to put sealer on your composite decking, there are drawbacks that you should consider. As mentioned, you will void the warranty of your decking boards if your manufacturers advise against it, and you could potentially waste money by doing so.

Another disadvantage of sealing composite decking is, ironically, the maintenance cost. While it makes the deck easier to clean, you will need to regularly re-seal the decking once you start doing it. While it may not seem like much, the costs can increase over the years.

We have listed some further disadvantages below:

  1. · Challenges with application: Applying a sealant to your decking can be a labour-orientated job in many cases. The process will consist of cleaning and preparing the surface so that it is ready for application.
  2. · Cost: Good sealants can be rather expensive, particularly for larger decking areas. The cost of sealants and labour surrounding the application is something to be considered when estimating costs for your decking project. With that being said, the process of sealing can be costly on the forefront however it will save you money over time.
  3. · Environmental Impact: Several sealants contain volatile organic compounds (VOCs) or other chemicals that can cause damage to the environment, along with surrounding soil and plants. To reduce any environment impact our advise would be to use a water based sealant.

There are pros and cons to applying sealant to your composite decking, in our professional view as long as you clean your composite deck, install correctly and maintain it regularly, you shouldn’t meet any huge issues and there shouldn’t be a reason for sealing.

Depending on the level of care and maintain over the years, we personally would only say its worth it some years down the line to enhance its visual appearance and extend its life span, if you feel its required. If you do below we discuss how to seal your composite deck.

Sealing Composite Decking

  1. Clean your composite decking thoroughly, ensuring to remove any dirt or debris from the decking surface. You can complete this process quickly and conveniently with dishwasher soap and warm water, brushing gently into the deck surface using a soft bristle brush. Avoiding any harsh chemicals when cleaning, such as bleach. To learn more about how to accurately clean and maintain your composite decking, check out our article.
  2. Ensure the product you use is safe for composite decking. Not only do you need to ensure the sealant won’t damage your decking surface, but you will be satisfied with the project once it’s complete. Water-based sealants are preferable compared to solvent-based ones, as they don’t alter the colour of the composite boards.
  3. Always read the instructions on the sealant before attempting to apply it to your decking. You will find essential information such as drying time, the number of coats needed and time allotted between coats in the instructions of your sealant.
  4. You can apply your sealant with a roller, brush or spray. Apply an even layer to your decking surface to avoid darker spots.
  5. It is also important to apply only as much sealant as the composite decking can easily absorb. Wipe off any excess product; if you apply more sealant than the composite material can absorb, it will puddle on the surface and dry, leaving shiny spots on your composite decking. Furthermore, these spots will tend to flake and peel.
  6. Please allow time for sealants to dry when applying additional layers.
  7. Leave it to dry. You must allow the sealant to thoroughly dry once you have finished sealing your decking.


Whilst sealing is needed for timber decking, composite decking often eliminates the need for sealing. First-generation composite boards do absorb more moisture and do fade more when compared to second generation boards. This may in time start your research in ways to improvement or enhance the appearance of your first generation boards. A sealant can be applied to help with this, but please note it will need consistent reapplying and most sealants don’t take well to the surface of composite boards.

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