This post was updated on April 4, 2025
Why Did Deck Stain Turned Black
Stain Turned Black
We appreciate you visiting Deckstainhelp.com as we continue to be your go-to source for the latest in deck restoration news and trending topics through 2026. Below, we talk about Why Deck Stains Turn Black. Feel free to leave a comment below with any pictures you may have.
Why Did My Deck Stain Darken or Turn Black?
There has always been some concern for deck owners as to why a deck stain can darken or turn black in color after a couple of years. There typically are a few reasons why this may occur for any brand of deck stain.
Improper Curing of Deck Stain
When a deck stain does not cure or dry properly it can remain tacky for longer than it should. This can result in embedded dirt, grime, and/or tree pollen. These trapped contaminants can have an increased effect on mold and mildew growth darkening the deck stain. Improper curing usually happens from over applying the stain.
Mold/Mildew Prone Climates
In very hot and humid climate types, mold and mildew can actually begin to form on the surface of a deck stain causing it to appear darker. In extreme cases, mold and mildew can grow below or in the stain, further darkening the appearance.
Applying an Inferior Deck Stain
As mentioned, mold and mildew growth can darken a deck stain considerably. Cheaper deck stains lack the formula to fight off mold and mildew. To lower the stain’s cost, some inferior stains contain a “cheap grade” of linseed oil without mildewcide additives to battle mold and mildew growth.
Tips to Avoid Deck Stain Darkening
Most deck stains are prone to darkening if the right circumstances occur. The darkening effect does not seem to be related to just one brand of wood deck stain but certain brands do seem to have issues more so than others.
Correctly prepping the wood prior to a stain application can certainly cut down the chances of stain darkening. Once a deck stain does seem to have darkened, it should be cleaned or removed completely before a new coat of stain is applied.
Be sure to follow the stain manufacturer’s instructions for cleaning the wood and applying stain. Be careful not to over apply the deck stain which can lead to curing issues. Back brush or use a stain rag to wipe any excess stain or puddles.
Use a high-quality deck stain that fights mold and mildew and is less prone to darkening.
Need Help With a Failed Stain that Turned Black? Ask Below.
Did two coats of ready seal cedar stain and deck is basically black. Had used stripper and brightener at least twice before sanding. Any hope of this lightening up at all? Re- stripping is not an option at this point. Thanks
It will fade most likley.
Thanks. Great site.
Top Photo on left shows exactly what the problem with my boards is. This is the only web site that told me what I needed to know. Thanks.
From many years of experience most of the issues in this thread are sourced from over application of oil based or alkyd acrylic toners on decks that haven’t greyed or aged with sun prior to washing and staining. Its understandable as proud owners want their decks to look like a magazine cover but too much product or too frequent oil applications for fear of water is problematic. Strip them gently, let the sun beat down, make sure your gaps are clear, then prep and stain. Its also important to factor sun orientation and shade as this may require different approaches.
Hey all. I stripped my old cedar deck. Stripped by sanding to bear wood in most places. Used Gemini safe stripper in a few areas. All areas were cleaned and brightened following with restor-a-deck. Waited 2 days, on main deck, longer for rails… applied TWP100 rustic. It looked great. It sprinkled 2 nights after staining. Water beaded up. Looks great. Then about 5 days after staining I spilled a bottle of water and notice a grayish black stain formed when the water evaporated. Then it rained and the whole deck turned black. Photos attached. What happened… what to do? This occurred in hours as the heavy rain fell. It can’t be mildew… it seems chemical?
Help
Might be rust. How did you sand it?
Orbital sander. Zirconia sanding disks. Think that given that it is so wide spread, It can’t be rust- could it?
It does indeed look like some form of chemical interaction. Any other thoughts?
If it was rust, how might we get rid of it? What would be options? Could it be bad product?
Rust turns black in wood when it gets wet. We have seen issues where people have steel wooled their entire deck and it turns black. If it is rust, a wood brightener that is citric or oxalic based would help to remove it. It is definitely a weird reaction but not sure what it is. It is reacting with the water once it hits the deck. Definitely not the stain.
You got me thinking. Several days after staining, we cleaned the metal railings you see in the pic with steel wool. We did that using the deck as our work place. So it could be scattered dust from that that wind spread over the whole surface…. wow! If so it should be on the surface, not deep in the wood? So might a brightener bring it all back? If so, is the stain impacted? Will I get shorter life etc? Thanks
If rust it should remove it. Nost sure if it harms the stain, doubt it.
I had some RestorADeck brightener I had mixed up 2= weeks ago. I helped, but didn’t fix. Does brightener age and become less effective? Is there a best brightener to use? Can I buy any brightener or are some stronger and better? This is with about 20 min of dwell time. Thanks for the help…
Left 2 are after. Right is before
Brightener does not age. I think your issue is because you have the wood stained. You may have to strip it all off and then brighten to fix this.
Ugh… what about using cleaner any chance that could help? Followed with brightener? Or will that just open up the wood pores and make it get dirty faster and undermine the stain
Or might something like bleach or oxiclean help?
You could try it but doubt it will help and the bleach will damage the stain.
So if I strip, brighten and restain will it fix it? Or do I need to sand all of this off?
That should fix it.
I used SuperDeck Oil-Based Transparent stain and noticed that it looked good in the beginning but slowly it got dark as you can see in the picture, the skirt of the deck looks okay but the top is just horrible.
I’m able to clean with a stiff brush but when I did this last season it looked like it lifted the stain off.
Do I need to strip this down and start over? Do you recommend sanding before applying the stain? The deck is entering it’s 3rd season.
Super Deck has an issue with darkening or turning black. Best to strip it down and go with a stain that will not do this. Strip and brighten with Restore A Deck Stripper/Brightener Kits. Stain with TWP stains or Restore-A-Deck Semi-Transparent stains.
pls see attached picture as requested, it’s not dirt or mould, thank you for your help.
hello, I treated each deck plank prior to painting them with four coats of grey decking paint before they were fitted to the frame and it looked great – sadly 3 months later there are brown marks all along the decking which I thought was dirt from rain (we haven’t used it much to get it dirty as it’s winter) but when I tried to clean it off with patio cleaner it’s not touched it, also tried a spurt from the jet washer and all that did was start to strip the paint off but the marks are still there and it looks awful. The staining seems to be coming though the paint from the wood below but it can’t be mould as it’s too new, any idea what it is & how to treat it please? I don’t want to re-paint until I know what’s causing it otherwise it’s just covering up the problem. Thank you for your time.
Post a picture.
pls see attached picture as requested, it’s not dirt or mould, thank you for your help.
Not sure what it is but we have never seen anything like this bleed up through a stain or paint. Most likely it is a stain of some sort from the elements.
ok, thank you for your help
How do I remove the black spots?
Depends on what caused the black spots. Not one reason for all scenarios. Pictures help.
What is the best way to cure and prevent future excessive blackening? I also have spots where the stain has come off. Thank you
Remove the current stain and go with a brand that does not turn black. Restore A Deck Wood Stain or Defy Extreme.
Woodstain dark oak went black in 30min in the can. What went wrong?
Sorry, no idea on this one.
The deck “professional” I hired to stain my brand new deck was supposed to sand the new wood before applying stain instead of power washing, which I read was fine if new deck. Unfortunately he did neither and applied the stain over dirt. Now it looks like mold underneath. After power washing, I sanded one of the worst boards to see if it would go away, but still see it. Can’t seem to go deep enough. What do I do? Please help!
It actually does not look like dirt but part of the wood. Just redo next Spring by stripping and brightening to prep.
I followed cleaning and application steps exactly for using Superdeck wood cleaner and Superdeck transparent stain Natural. Wood looked good after cleaning but within 24 hours of applying stain/oil the wood has turned black. I’ve used this exact product and procedure for at least the past 4 years every spring. What can be the cause for the black coloration this year?
Pictures please.
Well, I talked to Customer Service at SuperDeck who were very cordial……………however, their suggestion was to use a stripper to remove all JUST applied oil/stain. then use a brightener before reapplying stain. I’ve done this and it does look better than the black but what a lot of extra work and EXPENSE. I don’t feel there adequate info or instruction on any of the product labels…………and there was no offer of reimbursement for product already purchased and used. I’m not all that happy with SuperDeck The end result may be satisfactory but I think there needs to be better preliminary info. Photo 1 – after stripper, Photo 2, before stripper/after oiled, Photo 3 after wood cleaner, before oil.
Switch brands. The Super Deck has a histroy of turning black.
How do I get the “black stain” off of my deck?
Depends on what the “black stain” is and brand?
HELP! I used Thompson’s water sealer on my NEW deck and now there is dark spots like mold all of the deck!? Applied Thompson’s water sealer 7 days ago, weather has been nice and warm, rained one or two times, but its been 7 days!?!? This is a $7000 deck!!! Why did this happen and what can I do?
Hard to say what caused it. Please post a picture.
My deck was just stained for the first time with an oil based stain. The wood is pressure treated pine. Several boards showed some moderated 'blackening' prior to the staining. I had assumed that the company doing the staining would us a deck cleaning agent prior to staining. Now, after the stain has been applied several boards, including but not limited to those which showed pre stain darkening, are nearly black. In some places, the blackening appears to have drips, which suggest the oil stain itself is the problem. The deck had aged one year prior to staining and had not had any prior post completion treatment. The look of the 'finished' effort is terrible at this point. Is the likely culprit the stain (applied two days ago) or poor wood preparation prior to staining, or something else.
Strip and brighten and start over with a better stain.
Our deck is cedar. It is about 6 years old. We have stained it 3 times in those years. A black mess creeps all over it-not sure if its mildew or not. It is in the sun, no trees around it. Have power-washed and redone it twice. It is a horrible black mess again. [When the black stuff is wet it is slimy and slippery.] Need to re-do it but we don't know what to do. We have gotten lots of suggestions, but still not sure what to do. It has already cost us a lot of time and money! Help!
Strip and brighten for prep and try a stain that does not darken or attract mold. TWP 100 Series or Defy Extreme. One thing you cannot control is general dirt and grime.
Help! My pool deck is about 4 years old, when it was new I water proofed it with Thompsons Water Sealer. Lately the deck was showing signs of mildew and I knew I needed to clean and re-seal it. I used a good wood deck cleaner with wood brightner in it followed with power washing. The deck looked really good. I knew I had to seal it because the wood was stripped of all weather seal now, so I purchased 3 gal. of Thompsons Water Seal Waterproofing Wood Protector Clear. I applied it later in the evening after the shade was over the deck with a paint pad attached to a pole. The application was easy. The wood took the stain as soon as I applied it was soaking into the dry wood. It was dray by the end of the next day since we have had sunny days. I noticed the first day the wood looking darker, but waited another day to see if it would dry more and lighten up, but it hasn't. I really don't like the blackish color that the sealer has brought out. It looks like it has mold throughout the boards? It looks worse than when I first cleaned it? What are my options now to cover this mess?. Can I apply a colored stain over it, or should I clean and power wash it again? This deck gets a lot of sun all day.
You should strip it and start over. You cannot fix the issue by adding product on top.
I used RAD stripper and brightener. Now have a lot of black when wet assume it will be that way if stained with the TWP STAIN 1530 I bought. So how do I get he black out that has now appeared? It did a great job on railings but deck looks awful when wet. When if was dry yesterday looked fine raining now and a lot of black again? Will is look like that if I apply the stain once dry again? I ask this once before but did not see a response. maybe I am not looking at the right place . Please help. THANKS
Dee, it will probably show when stained. Might want to re brighten the wood and see if that helps to remove some of the darkening.
Ok will try that was wondering if I am going to need to sand it . ???? Thanks for you help
brightened a second time and cannot tell a lot of difference . Other suggestions
Thanks
Dee, try a watered down bleach solution?
I tried a double strength of brightener 16oz/gal (all the brightener I had left)very little improvement if any. Seems now stripped if ever gets dried out with our weather I may have to live with the blackening after the stripping..something I had not expected but need to stain ASAP or so I think . I suppose it will protect the wood regardless of color that was left behind from the stripping. Also tried a diluted beach solution and that yielded no positive results either. It is an older deck and has looked really good until now with caring for every couple of years.The last time using a stain with pigment and needed to strip this time The new treated wood does not seem to have near the life expectancy of this older wood so doing my best to care for it.
Thanks a bunch for your help!
I have a southwest-facing deck in Minnesota, cedar. Two years ago sanded entire deck to remove a peeling semi-solid water based stain (Sherwin Williams?) previous owner had applied. That was a lot of work. With a clean bare wood applied Penofin Red Rosewood Oil (Redwood color)….Deck was beautiful year 1. Year 2, deck was looking as if needed reapplication (wear in higher traffic areas). Reapplied Penofin Red Rosewood Oil, with correct wiping technique, but deck remained very tacky for many days after application, then began to turn black. Now deck has some black mildew growing. Want to try TWP 100 or 1500, but not sure about old Penofin product, does it need to be completely removed (stripped?) or sanded, don't want to go through that again if it can be avoided…..What prep work would need to be done to either 1) fix the Penofin finish or 2) prep for a TWP application?
Amy, yes it needs to be removed completely with a stain stripper then brightened. Try the RAD products for this.