Composite decks are made from a blend of wood particles, plastic, and various other materials. They are preferred over traditional decks because they require very little maintenance to keep them looking good. However, a lot of people are unclear about just how much upkeep their deck needs.
Manufacturers often use the fact that their decks don’t need sealer as a selling point. But it’s not quite as clear-cut as that. Although new decking is very durable, it is still prone to some wear over time and there are some benefits to using sealer.
This article will tell you everything you need to know about sealing composite decks and help you find the best products for your deck.
Do New Composite Decks Need Sealer?
No, new composite decks do not require sealing. Composite decking is made from a blend of recycled plastics and wood fiber, which gives it the appearance of wood but makes it more durable. The materials used are designed to protect against mold and mildew, as well as stand up to the weather.
If you check the manufacturer’s guidelines, you will see that they do not advise sealing. In fact, some composite decking could even be damaged if you apply sealer, and your warranty will be voided if you do so.
However, if you have had your composite deck for a long time you may want to consider applying a sealer.
Why Do Old Composite Decks Need Sealer?
Old composite decks do need sealer because they wear over time. Although they are designed to be more resistant to mold and mildew, that doesn’t mean they are completely free from staining. UV rays will also cause the color to fade over the years, ruining the appearance of the decking. A new composite deck will not absorb water, but an old one will. Test your deck by putting a few drops of water on it to see whether it soaks in or not. If it does, it’s time to seal your deck.
When you seal your deck, it will prevent mold, mildew, and stains from forming. Some brands of sealer can also stop fading caused by UV rays. Having the protective coating on your deck means that maintenance is easier too because you don’t need to clean your decking as often.
So, even though manufacturers claim that their decking never needs to be sealed, it is good practice to use a sealer on old composite decking to keep it in good condition and extend its lifespan.
How Do You Seal a Composite Deck?
Following the correct procedure is key when sealing your composite deck. These are the steps you must follow:
1. Clean the Old Composite Decking
Before you can apply a sealer to your composite decking, the surface needs to be clean. All mold, mildew, and stains need to be removed before the product is applied or they will be trapped under the protective seal and will continue to grow on the wood.
You can use a simple diluted laundry bleach solution, an environmentally-friendly all-purpose cleaner, or a specifically formulated deck cleaner. There are a lot of great products on the market, like the DEFY Composite Deck Cleaner. This oxygen bleach-based cleaner will soak deep into the wood and lift stains instead of just removing the surface layer.
2. Let the Composite Deck Completely Dry
Once you are happy that the deck is completely clean and free from any mold or mildew, you need to let it dry. It’s important that you let the decking dry fully so that the sealer can do its job properly. If there is still moisture present, the sealer may not apply properly. It can also increase the chances of mold and mildew in the future because that moisture is locked in. So, give it at least 24 hours for the surface to dry out before sealing your composite decking.
3. Apply the Sealer
Once the deck is clean and dry, you can apply the sealer by either brushing it on, rolling it, or spraying it. There are different types of sealer available so check the manufacturer’s guidelines to find out which option is best for your product.
It’s important that you follow the manufacturer’s instructions carefully when sealing your composite decking because they all have different requirements, like how many coats should be applied, how thick to apply the product, etc. If any steps are missed or if there isn’t enough product applied then it may not protect your deck properly.
5 Best Sealers For Composite Decking
Finding suitable products for your decking will ensure that it is not damaged and it is protected for as long as possible. These are the 5 best sealers for composite decking on the market right now.
1. DEFY Crystal Clear Composite Deck Waterproofing Sealer 
DEFY Crystal Clear Composite Deck Waterproofing Sealer is a water-based sealer that is completely clear, so it will protect your deck without changing its appearance. It’s extremely durable and prevents black stains from mold and mildew from coming back once your deck is cleaned. It also offers amazing protection from the sun due to the zinc nanoparticle technology. Similar nanoparticle technology is used in sunscreen and the same concept applies in this deck stain; the tiny particles reflect the UV rays so they cannot penetrate the deck and cause fading.
You only need to apply one coat of this sealer for full protection and a gallon will cover 200-300 square feet of decking.
2. Olympic Stain Smartguard Concentrated Multi-Surface Sealant
Olympic Stain Smartguard is a water-based sealer that comes in a concentrated form so all you need to do is add the pouch to 2 gallons of water and mix thoroughly. Each pouch will cover 500 square feet of decking with a clear sealer.
It’s suitable for all exterior surfaces so can be used on decks, fencing, siding, roofs, and more. It also offers 50% more protection from UV rays than other seals. You don’t even need to scrub the decking before using this product; just spray it on and allow it to dry. It penetrates deeply into the wood to protect from within too. You can even apply it directly after rain or cleaning and it dries in an hour, so you can use the deck on the same day.
Although the application process is incredibly simple, you still get great protection against water damage, mold, and mildew.
3. Resist Mist Deck Armor Sealer 
The Resist Mist sealer is designed to create a ‘never scrub again’ surface on your decking. The first time, you need to dilute the concentrated sealer, spray it on, and then leave it 5 minutes before you scrub and rinse off. After the first application, you can simply clean the deck, let it dry, and spray more sealer on every 3 years to boost the protection.
It’s a non-toxic, water-based product that can easily lift green and black stains and oil-based stains from things like suntan lotion. The concentrated formula, mixed with 2 gallons of water, will cover roughly 600 square meters of decking with a clear seal. However, it may not go as far with older decking because more product is required to give a good coating.
4. Rust-oleum Composite Deck Refresh 
Rust-oleum Composite Deck Refresh seal is perfect for restoring the color to old, faded composite decks. It’s a simple one-coat application that will cover up to 300 square feet. This is less than other sealers, but it has a strong redwood color instead of a clear seal, so you need to apply a thicker coat.
Once dried, it provides excellent water-repellent qualities and protects against UV rays and mold, and mildew growth. Although it may not restore the exact color of your old decking, it will breathe new life into old, faded composite decks so you don’t need to replace them.
5. Messmers Composite Deck Finish 
Messmers GAL Russet Deck Stain is a tough, durable deck finish that can restore color and protect decking. It is available in a range of colors, including Cedar, Russet, Navajo Red, Cape Cod Gray, Natural (green), and Oxford Brown. Although these colors might not match the exact tone of your deck, you can find something very close.
It provides excellent mildew resistance and stain prevention once applied, and it protects against UV rays too. Each gallon will cover 100-250 square feet and should be applied every 1 to 2 years, depending on how harsh the weather conditions in your area are.
These are all excellent sealers to bring your old composite deck to life and protect it from damage.
See some of my related composite decking guides here:
- Can You Screw into Composite Decking?
- Can You Paint Composite Decking? (All You Need to Know)
- How to Finish the Ends of Composite Decking?
- Is Composite Decking Fire Resistant?
- Pros and Cons of Composite Decking
- Can You Use Ice Melt on Composite Decking?
- How Wide Are Composite Deck Boards? (Profile & Size Guide)
- 10 Best Composite Deck Cleaners For Mold and Mildew
- 7 Best Composite Decking Brands
- How to Keep Composite Decking Cool Enough to Walk On
- Is Composite Decking Slippery When Wet?
Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.