Hi, I’m Scott Paul, a licensed exterior restoration contractor with over 30 years of experience and 10,000+ deck restorations. This review of composite deck sealers and stains is based on my own hands-on field testing, not manufacturer claims. See my full credentials and testing stats here.
A composite deck sealer can bring an old, faded composite deck back to life and protect it from mold, mildew, and graying. Composite boards are a mix of plastic and wood fibers, so they are prone to many of the same problems as a wood deck. The catch is that only some composite will absorb a sealer, and choosing the wrong type of product leads to peeling. This page covers what to look for, which composite decks can be sealed, and the product I used on a very old Trex deck.
- Composite decks are prone to mold, mildew, fading, and graying caused by sun and water damage, making sealing essential.
- Look for a composite deck sealer that is durable, UV-resistant, and protects against mold and mildew.
- Sealers containing zinc particles naturally deter black mold, mildew, algae, and fungi while reflecting harmful UV rays.
- Avoid film-forming or solid sealers as they sit on the surface and are prone to peeling, flaking, and cracking.
- Quality composite sealers should penetrate the surface for maximum protection rather than forming a film on top.
- TWP Semi-Solid Pro-Series in Mount Rushmore was applied to an old Trex deck with outstanding results at about 200 sq ft per gallon.
Before sealing, the deck has to be fully clean. I use DEFY composite deck cleaner, and my guide on how to clean composite decking covers the full process.
In this review:
- Does a Composite Deck Need to Be Sealed?
- Which Composite Decks Can Be Sealed or Stained?
- What to Look for in a Composite Deck Sealer
- Clear Sealer vs. Semi Solid Stain on Composite
- My Trex Composite Test: TWP Semi Solid
- How to Seal or Stain a Composite Deck
- Composite Sealer FAQ
- Composite Deck Stain Photos
Does a Composite Deck Need to Be Sealed?
A composite deck does not need to be sealed when it is new, but older composite often benefits from it. Composite is not as vulnerable to the weather as wood, but it is still prone to mold, mildew, fading, and graying from sun and water. On older boards, a composite deck sealer slows all four and restores some of the original color.
Which Composite Decks Can Be Sealed or Stained?
Whether you can seal composite decking depends on whether the boards are capped. Most composite sold today is capped, meaning the core is wrapped in a protective plastic shell. Capped boards do not absorb sealer or stain, so anything you apply sits on the surface and peels. They only need regular cleaning.
Older, first generation composite is uncapped, so the wood fibers in the board are exposed. These boards absorb water, grow mold more readily, and fade over time, and they are the ones that benefit from a penetrating sealer or stain.
Simple test: Sprinkle water on a few clean, dry boards. If it soaks in, the composite will accept a penetrating product. If it beads up, do not seal or stain it.
What to Look for in a Composite Deck Sealer
- Penetrating, not film forming: A quality composite sealer soaks into the surface. Film forming and solid sealers sit on top and are prone to peeling, flaking, and cracking.
- UV protection: Sun fades most unprotected composite. Pigment or UV blockers help the deck hold its color longer.
- Mold and mildew resistance: Composite in shade or near trees grows black mold and algae, so a mildew resistant formula matters.
- Zinc particles: Products with zinc particles are a plus. Zinc is a natural deterrent to black mold, mildew, algae, and fungi, and it also helps reflect UV rays, acting like sunscreen for the composite surface.
Clear Sealer vs. Semi Solid Stain on Composite
| Clear Composite Sealer | Semi Solid Stain | |
|---|---|---|
| Color | Keeps the existing color | Adds new, even color |
| Hides fading and blotches | No | Yes |
| UV protection | Depends on formula | Strong, from heavy pigment |
| Best for | Uncapped composite that still looks good | Old, faded, or blotchy uncapped composite |
My Trex Composite Test: TWP Semi Solid
I prepped and stained a very old, dirty Trex deck in the spring of 2021 with the penetrating TWP Semi Solid Pro Series, and it turned out outstanding. The deck looked brand new, and the TWP soaked deep into the composite with no issues. If you want to add color to old composite decking, TWP Semi Solid is the product I recommend.
TWP Semi Solid Pro Series on Composite
- Deck: Very old, uncapped Trex composite, heavily soiled
- Prep materials: Restore A Deck Cleaner Kits
- Color used: TWP Semi Solid Mount Rushmore
- Coverage: 1 coat, 4.5 gallons used, about 200 sq. ft. per gallon
- Full review: TWP Semi Solid Pro Series Review
How to Seal or Stain a Composite Deck
- Clean the composite. Clean with an oxygen bleach composite deck cleaner to remove dirt, mold, and algae, then rinse thoroughly. Anything left on the surface blocks absorption.
- Let it dry. Allow at least 48 hours of dry weather so the boards are fully dry.
- Test for absorption. Sprinkle water on a few boards. If it soaks in, the composite will absorb a penetrating product. If it beads up, the boards are capped or sealed and should not be stained.
- Apply one thin coat. Apply one coat of penetrating composite sealer or semi solid stain with a brush, pad, or pump sprayer, a few boards at a time. Composite absorbs less than wood, so one coat is usually enough.
- Back brush the excess. Work the product into the surface and remove anything that pools or does not soak in. Excess left on composite will stay tacky and peel.
- Let it cure. Keep foot traffic off for 24 to 48 hours.
Composite Sealer FAQ
Can you seal composite decking?
Yes, if the boards are older uncapped composite that absorbs water. A penetrating composite sealer protects against fading, mold, and mildew. Newer capped composite does not absorb sealer and usually only needs cleaning.
Can you stain composite decking?
Yes, on older uncapped composite. I applied TWP Semi Solid to a very old Trex deck and it soaked in and looked new. Capped composite should not be stained because the product sits on the surface and peels.
What is the best sealer for composite decking?
A penetrating product rather than a film forming one. For adding color, I recommend TWP Semi Solid. Film forming and solid sealers tend to peel, flake, and crack on composite.
Do I need to clean composite decking before sealing?
Yes. Dirt, mold, and algae left on the surface block absorption. Clean with an oxygen bleach composite deck cleaner, rinse, and let the deck dry for 48 hours first.
Composite Deck Stain Photos
Have you sealed or stained a composite deck? Share your results, or ask a question with a photo of your boards in the comments below. I answer most questions within a day.
I spent alot of money installing a trex deck and three years later I am getting white spots and what looks like a white film. What can I do about it? Can I stain it? And How can I prevent it from continuing where it has started. How can I prevent this from starting on boards that are still in good condition?
Without knowing what it is and what is causing the white spots, there is no way to answer how to remove it or prevent it. Have you contacted Trex support for assistance? Pictures would help as well.
Hi. I’m looking to buy a clear composite deck sealer but struggling to find one, can you recommend please. Thanks
Defy Composite Sealer: https://www.deckstain.com/defy-composite-deck-sealer.html
What brand of composite deck sealer is the best?
Defy Composite Sealer.
Thanks for that however, I see this is over £100 for a 5ltr tin which seems a bit expensive and was wondering if there was a good alternative. Thanks
Nope.
I have an older Trex composite material deck .. it’s a real gray color. Is there a refinish product with a similar gray color? I purchased a Rust-Oleum composite refresher called Gray Tone. But it’s actually a taupe color.
Not that we know of.
What is the best caulk/filler for screw holes in old composite decking?
We recently purchased a house built in 1999 with a nearly 2000 sq ft elevated deck made of first generation light grey Trex decking. The Trex is actually in pretty good shape except for some staining (not mold related), but the support beams were rotted to the point that screws no longer held in place. We removed the Trex and replaced the beams. To save money and resources, we chose to clean and stain the Trex (solid color stain) and replace it. Lumber being what it is, some of the old screw holes did not exactly line up with the new beams, so there are a good number of empty screw holes I would like to fill in. What should I use? I tried some DAP Platinum and it cracked and bulged, and turned to a flakey powder. I need something that can be sanded or will maintain shape after being placed and can take a solid stain.
Thanks!
Try this. Gulf Synthetics PermaFill.
What brand of sealer is recommended for MoistureShield composite decking?
Defy Composite Sealer.
I unwittingly power washed my Trek Deck and if you can imagine stripped the top layer off. Now when it rains, tiny particles are released from the deck to the area below. The deck is brown and about 12 years old. Short of replacing the deck, any recommendations on how to fix this? Any advice would be greatly appreciated.
Sorry, but it cannot be fixed.
any decking restore should work ,some are sold at Home Depot
Itis the same decking restore used on wood that from a composite look and can have multiple coats to build it up
Those products will peel on composite.
Hello. I applied extreme composit sealer on my deck after I power washer it. Now I have white spots everywhere the water beaded up on the composit decking.
Post a picture.
Photo of white spots where the water beaded up. I applied defy extreme composit sealer yesterday. It rained this morning
That looks like mineral deposits from the rainwater. Try wiping it off with a wet rag.
You repeatedly say to use Defy sealer, however this question is asked more than once, what is the next brand to use for a sealer on a Trek deck?
There isn’t any that we know of. Defy makes the only decent composite sealer.
Our Timbertech is only a year old, but we are seeing many scuff marks from the patio furniture, as well as a light haze in some areas. Do you have any recommendations for hiding the scuff marks, and removing the haze? Any products that can darken the material (similar to what Armor All does for plastic)?
Sorry but no, that is not possible.
We have a Trex deck that is starting to really look bad along the edges that get more snow and rain. Also we have a couple of boards up the middle where it is covered looking bad. It is 14 years old. Trex even admitted that that old was not up to par. It’s a big deck we can’t afford to replace it. I read that Safe-T-Deck would make it permanent if we first used Super Primer then the seal coat. Do you know if this is accurate? What is your recommendation?
I am sorry but we do not have any experience with Safe-T-Deck. I do not it would be permanent but should help.
I had a composit deck for 14 yrs. It used to be light gray but looks kinda light blue now. I’m wanting to know if I can put a solid colored dark slate colored stain on it. What do you think?
Thank you
I do not think it will work. Most likely peel, but we have never tried.
I stained mine about 5 yrs ago it hasnt pealed yet
can I use valspar solid color deck stain on my composite deck?
No, I do not think so.
is defy the best composite sealer
Yes.
Does DEFY carry a stain for composite wood stain, not a sealer
No, just a sealer.
Will this sealer renew the color?
No it does not change or enhance the appearance.
what are the best sealers for a 1st generation trex deck
Try Defy Composite Sealers.
My composite deck is about 7-8 years old. It has lots of discoloration on it. About 3 years ago I cleaned it which got rid of the natural (mildew and/or algae I guess) stains and discoloration. I did not protect the deck with anything after the cleanup. Shortly after the cleaning I had my roof replaced. One of the shingles was dropped on the deck and stayed on it for some time. Now, 3 years later I have a very dirty deck again except for the spot where the shingle was. This spot is relatively nice and clean – I see the “imprint”, so to speak, of the shingle. Whatever material was coming out of the shingle ended up protecting the deck really well. Shingles are mostly petroleum and asphalt. Also, whatever it was, there was not a lot of it as at first I could neither see nor feel anything at that spot and only after a while the area where the shingle was started to stand out from the rest of the deck as being cleaner and not stained.
What do you think it could be? Whatever it was I suspect it would be (a) very cheap and (b) lasting (3 years in my case so far). With this experience I do not feel like buying a relatively expensive (~$200 – $300 for my somewhat bigger deck) sealer and reapply it (hours of work) each year or every two years as recommended by most of the manufacturers. What do you think about this? Thank you.
It has no discoloration or dirt because it covered the wood. No other reason we can think of. Oils will not prevent this nor would a shingle leach out oils.
What do you mean by saying: “It has no discoloration or dirt because it covered the wood.”? The shingle was there for a few hours, maybe a day and beyond that nothing was covering this area. It was a new shingle (not an old one) and they are oily when you touch them. Later on I will include a picture or two of this area.
Sorry you never said hours. I assumed “some time” meant a long time as in months or years.
Here are two pictures showing the spot where the shingle was. It happened in the fall 2014.
Whatever it did, it repelled the mildew from growing there. No idea why.
Any idea who may know, whom to ask? I asked the deck manufacturer and the shingle manufacturer but did not get anything from them. Whatever it is, it is cheap and effective so, I believe, it is worth figuring it out.
Sorry but no idea.
If it was a high end shingle, copper or zinc is used in manufacturing, and they both inhibit moss, algae, mold.
The answer to this is actually quite simple… modern shingles have zinc particles embedded to avoid mold and mildew growth – the sealer with zinc particles should have the same effect
Thank you for your comment!
Yes exactly! Didn’t see your post before my reply. Both, zinc or copper are in high quality shingles now days.
The shingle material laying on your deck, did not have any protection in it. The reason there was a clean spot is that the black algae (gleo capsa magma) need sunlight to thrive. Same thing on concrete and pool decks. When you take the pool cover off there is a clean spot underneath. No sunlight. no Black Algae.
I disagree with not using bleach on a deck. If you do not kill the black algae spore then you are wasting your time. We clean decks without power washing with our softwashing system with no damage or wear and tear from a pressure washer. Pressure washing a deck is like cutting the lawn, the algae will grow back stronger and darker.
It’s discouraging as I don’t see any sealer recommendations that are actually great products or worth their cost.
Anyone have any experience with Resist Mist Sealer? They claim it will prevent mold/mildew returning for as much as 3 years? Pricy but could be worth it if it actually does what it claims.
On cleaners diluted bleach is best.
No BLEACH NEVER! Use oxolic acid cleaners as recommended by Trex© Do some research on this stuff, as it has long been used in architectural restoration. Just make sure to thoroughly rinse, leave no puddles for residue to gather.
Which sealer do you highly recommend to use on my composite deck and please let know me know where I could purchase it.
Try the Defy Composite Sealer.
I have a composite deck that is only 6 years old and is really faded. I would like to make it pop again with luster like my picture below. what can I use?
Composite sealers will not “enhance” the grain. Nothing we know of will do this.
Is there anything that I can put in my trex deck to help be less slippery?
Sorry but we do not know of anything.
As a former OSHA© Compliance Officer, I recommend a few stategically placed peel-n-stuck anti-skid strips, you can get some nearly transparent ones. Just realize for the sake of safety, these are not covered under warranties, and to remove later, use only Trex© recommended Magic Eraser© (dry erase) never use any solvent-based product. I hesitate but do suggest using outdoor runners (with non-marring gripper rug pads underneath). Runners can be the culprit in ‘Slips-Trips&Falls’ though so please keep properly flat, discontinue use if corners start to curl up!
Also-when using any rugs/runners, ALWAYS lift and dryout after rain, slightly repositioning area each time to prevent sun-fade, & mildew, as most products are “mildew- resistant not mildew-proof!
Trying to find a sealer that might give a no slip action to the boards. My dogs slid all over it. Anyone have one they have used?
Thanks,
Lisa
A sealer will not do this. Sorry.
So what composite deck sealers do you recommend?
Defy composite sealer.
Do you know of anything that can be applied to make the decking appear darker, more of a “wet” appearance?
No, never seen a sealer that will enhance like a wet look.
I accidentally dropped some thompsons water seal on my composite deck and it has left that “wet look” that you mention, been about a week and darket than the rest of my deck
That will go away soon.
I already cleaned my composit deck with Behr deck cleaner at one time there was a Behr Sealer
where can I purchase just the sealaer Home Depot don’t carry it?
We have an old composite deck, light gray in color, on our cabin in the mountains. It is approximately 20 years old. Do not know brand or what it is actually made of. It leaves chalky mess on shoes and clothing when rubbing up against it. Can we seal it, and if so with what? We need to remedy this problem without having to replace the whole deck. It is very large.
I do not think sealing this would stop the white chalky. Sealers are not designed for this.
How is that Defy clear composite sealer I want to give it a try but have seen some bad reviews on it that it doesn’t work as advertised I’m asking because like anything people have different opinions of products as I have seen by reviews some love it and swear by it where others just didn’t like the product at all stuck between is it good or is it bad because at $50 for a gallon its kind of on the expensive side is there any other composite deck sealers out there what do the Professionals use?
We have used it about a dozen times in the last few years. Never had an issue with it. Prep is key, meaning all the mold needs so tbe removed or killed first. ff you decide to use it, please post your results here.
What is the best way to remove the mold and mildew. I’m cleaning my composite with Simple Green and it seems to be doing a good job. Is there a better product?
A deck cleaner like the Restore A Deck Cleaner. If really deep mildew stains, bleach will work. Water is down 1 part to 4 parts water.
WASH SAFE great product, l purchased two gallons on Amazon. I have a 16’x20’ size deck with 10 steps . I followed the instructions of 4 parts water to one gallon. Make sure to use hot water. I’ve been using Simple Green. There is no comparison, WASH SAFE really made my deck look great ( like new) you need to follow the instructions which are easy and simple. I rinsed using my pressure washer. Per the instructions it’s recommended that’s a sealer should be used to complete the job. I washed my deck yesterday 10-23-2017. My problem is finding a Recommened good sealer and where to purchase it. The Home Depot and Lowe’s don’t sale composite deck sealers. I checked with my Benjamin Moore neighborhood store they carry a sealer which cost $73.00 ! They would need to order it. I need it like now. I don’t want to waste my time and money on Dufy compsite sealer to many bad reviews. Any recommendations?
Great Site!…Live in Seattle area. Built a 10 x 12 deck using mainly cedar. Utilized 4×4 PT Fence Posts for better strength. Used 'Flood' CWF-UV (translucient-Cedar Tone). I discovered your site AFTER using 'Flood' CWF-UV deck stain.
A friend gave me about 300 lf of gray ChoiceDek after I already built my deck with cedar. (ChoiceDek was sitting side of his house for about 5 yrs)…figured I would use Choicefek to build 2 benches (utilizing Dekmate Bench Brackets) stairs and as much of the railing as I could.
My challenge of course, is incorporating the gray ChoiceDek into my newly built cedar…which I'm thinking I will need to paint, most likely a solid color…which if I understand correctly, is the opposite of what your site recommends.
I'm trying to be as cost effective as possible so would really like to incorporate the ChoiceDek (as opposed to purchasing more cedar)…assuming I can solve the issue of painting the ChoiceDek to somewhat match the deck's current color.
Recommendations/Suggestions?
Thanks in advance,
Scott
Issaquah, WA
Sorry but not sure if you can paint the ChoiceDek or not. I would contact them for suggestions.
need product name for good composite deck sealer
Try the Defy brand.
My composite deck has faded and seems somewhat beaten by the upstate NY weather. Indeed, there is not such a thing as a maintenance free deck! I'd like to rejuvenate it with some sort of penetrating stain. I've seen advertised that some wood stains will also go on composite. Is this correct or is there something out there specific for the job? Any recommendation would be appreciated.
Some stains will work on composite decking. We have used them in the past but rarely in the last 8 years. We tried the Messmers Composite sealer with some success.
We are in need of a color stain for our Trex deck in saddle match?
Any brands and color names???