This post was updated on May 1, 2024
Why Did my Deck Stain Turn Black?
We appreciate it when people write in and ask for advice when something goes wrong during their deck staining projects. Today we talk about what causes your deck stain to turn black after a year or two and what to do to get rid of the problem. We appreciate your input, so feel free to leave a comment below with pictures of your deck stain projects.
Black Deck Stain
Why Did Your Deck Stain Turn Black?
Many things can happen to a deck stain when it is not applied or maintained properly. The biggest reason for a deck stain turning black is mildew. All wood surfaces need to be cleaned correctly prior to staining. The use of a quality wood cleaner and pressure washer or scrub brush is necessary to remove all the contaminants like dirt, grime, mold, mildew, and graying.
When contaminants are left in the wood pores and stain is applied a whole host of problems can occur. Mildew can begin to grow underneath the deck stain, which causes discoloring. This can also lead to rot and decay because if there is mildew there is also moisture present.
Best Cleaner to Remove Mildew on Deck Stains
The RAD Guard will remove the black mildew and green algae stains from your wood and deck stains and will prevent them from returning for 1-2 years: RAD Guard Mildew and Algae Cleaner and PreventerAnother reason your deck stain turned black can be from using an inferior stain. Cheap quality deck stains do not contain the mildewcides and inhibitors that more quality deck stains have. The mildew or black discoloration can occur on top of poor-quality stains. Some low-quality deck stains can even be the cause of mildew infiltration. Some cheaper deck stains can actually cause mildew to grow in certain conditions.
To cure a deck that has turned black you will need to strip the wood using a quality wood deck stain stripper or wood deck cleaner. Remove all the old existing deck stains along with any graying, mildew, and other contaminants. Wash the deck several times if need be. Once all the wood is clean and allowed to dry for several days, apply a quality deck stain that contains mildewcides and mold/mildew inhibitors so the darkening of the stain does not reoccur. Proper maintenance should include a light wash every couple of years followed by a recoat of the same quality deck stain.
I stained my deck in early July. I cleaned, power washed, sanded…waited more than a week for drying…no rain. Then I used Sherwin-Williams Super Deck Solid Stain. I gave deck two coats. No walking on deck for over a week. Just recently 5 weeks later I noticed some black residue or spotting on several of the boards. They were not there earlier. May I paint over them? And also, what is your opinion in giving the deck another coat after it’s been 5 weeks? Thanks. Robert, West Laurel, MD Here are pics.
That looks like mold. Try this product to clean and prevent it before reapplying more stain.
https://www.deckstainhelp.com/rad-guard-mildew-cleaner-preventer-review/
It may take a few weeks to clean it off after applying it.
We had a deck that was not in great shape re-stained and these black spots showed up. According to the company, they pressure washed it with 2500 PSI, applied deck detergent SW “revive” , and lightly sanded the area for a “smooth and splinter free finish”. They then applied Sikkens/Pro-Luxe “SRD” semi transparent stain. I’m not concerned about the knots and the color variation but it almost looks like permanent dirt is on the boards. If I try I can scratch it with my fingernail and it exposes the wood beneath.
Looks like it was bad prep of not cleaning/stripping correctly and they left wood furring that was not sanded correctly for a “smooth and splinter free finish”. https://www.deckstainhelp.com/wood-fuzzies-furring-on-deck/
If you can live with the appearance then I would not worry about it. You can fix it when you redo in the future.
Have a delay in staining and have a few of those shiny spots left. They have been sanded and what is left is rough. Will stain stick to these spots? If I use some paint stripper on those spots will I need to brighten again? Is there a good way to clean if I utilize a paint stripper?
Post pics and it varies based on the stain brand and type you are using.
Here are a couple of pics. One sent before sanding and two after sanding. I will be using TWP 100. Thanks
In the first pic, we would sand ot strip that. The rest is pretty minor and should be okay if you have a similar color so it blends.
Deck is stripped and I did some light sanding. Used brightener after both steps and the wood is dry. I have a window where the stain will have 24 hours to set before a possibility of rain appears. Is this long enough to prevent any damage to the surface? I will be using TWP 100.
Yes.
Thanks for your help but need more guidance. Stripped and brightened most of the deck but it looks like it needs sanding or more stripping. I am sending pics. If I need to sanding I anticipate using a belt sander on the deck. What is the best grit to use if sanding is the solution? Also, I am sending pics of some areas where some of the old stain is not coming off. It has a sheen. Should I give the stripper one more shot or will some sanding on it make it receptive to stain? Some white residue appears on posts. Try removing it with power sprayer and some came off. It looks as if it may be a non issue when stained. If not let me know
It looks shiny like a varnish. Either sand:
https://www.deckstainhelp.com/how-to-sand-your-wood-deck/
Or use the RAD Paint Strip for these areas:
https://www.deckstainhelp.com/rad-paintstrip-paint-solid-stain-stripping-gel-review/
I will be using pump sprayers for both brightener and stripper. Do both stay active if sit in the tank for a couple of hours
Yes for the stripper and the brightener. Not the Cleaner.
I am getting ready to redo my redwood deck. I will be using the RAD stripper and brightener to prep. Deck is right next to the house which is stucco. Concerned that the stripper may affect the stucco or the stain removed will stick to it when power washing. I will be attempting to use a board to keep as much off as possible. Tape wont stick to stucco so masking it off is useless. Do you have any experience with this?
You will need to keep it off the stucco. Try large 4×8 sheets of plywood to block.
Hi,
I’m working on a weathered deck that had been previously stained/sealed with Armstrong-Clark stain/sealer. I power washed cleaned the deck using 30 sec cleaner and once dried followed with sanding down boards using 80 grit paper. I vacuumed and I let stand for ~ 2-4 weeks. When I applied the stain on sma small section this is how my test section turned out. I included a before section of the deck and after. Any advice would be helpful..thanks!
The darkening is internal. Did you brighten after sanding?
Thanks for the prompt reply..Just sanded. I have a wood brightner (Defy). Would the recommendation at this point (given the darkening) be to just brighten the unstained boards and then stain when dry, or to first use a cleaner then brighten before staining. I’ll probably have to strip and redo the test section again, correct?
Yes, you would have to strip and then brighten all. No need for Cleaner. Does the internal darkening show when just wet with water?
I just applied the stain yesterday and it was pretty noticeable immediately following applying the stain. I don’t imagine it would change throughout the day..would there be a difference on how to approach. I was just afraid there was more mildew from letting it sit. Thanks again for your help!
It is not mildew but internal discoloration from the 30 second cleaner or sanding. Brightener typically fixes it.
I’ll get on it today. Thank you again for the help; I really appreciate it!
Applied the brightner and even after rinsing I’m noticing these darker patches persist. Shoud
I be worried? Will these result in that patchiness when the stain is put on?
Thanks again.
Yes, that is internal, so it will be darker when stained. If the brightener did not remove it, then nothing will. It is part of your wood grain.
What kind or brand of brightener did you use?
Defy Brightner mixed as instructed. It does say for heavier weathered or soiled areas that the concentrate not diluted could be used. Is there another brand that you would recommend?
Not sure if a different brightener would matter.
I should mention my major concern was it was a problem with how I prepped the deck, either inadequate sanding, cleaning etc. This is really the first exterior deck I’ve worked on to restore, so just don’t have experience with the expected result.
if it’s part of the grain and in your opinion acceptable, then I am content with the result. Maybe a different stain would be a better option? Went with the one the previous home owner had selected just for continuity purposes.
Thanks again for the advice and help!
It could be that when you sanded, you “burned” the wood by getting too close. This will not come out with a brightener. Using a darker brown color would hide this imperfection compared to a reddish color.
The last 2 years I have been staining my 350 sqft PT deck with Armstrong Clark Stain (Natural Tone) and I cannot say I am very impressed with it. After 3-4 months following the application of the stain it turns black and looks absolutely terrible. I am always thorough with the prep and follow the instructions diligently. I use the Restore a Deck Cleaner and Restore a Deck Brightener as recommended on this website which works great resulting in a very clean deck.
These are the steps I take:
1) Sand (if required) clean edges, gaps and vaccum throughly
2) Wet deck, Spray on Cleaner and let stand for 15-20mins keeping it wet; Scrub with Deck brush and pressure wash off. Do this until water run off is clear.
3) Apply RAD Brightener thoroughly let stand for 10 mins keeping it wet. Pressure wash off and do this until water run off is clear.
4) After 48 hours, apply the deck stain using a sprayer and back brush it into the planks with a deck brush. Brush the stain on the railings using a deck brush.
5) Check for tackiness after 8 hours and wipe as required with lint free cloth
6) Let dry for 24 hours before walking on deck
I am completely baffled as to what I may be doing wrong as this deck is less then 6 years old and prior to contacting AC I would like to hear any feedback on what could possibly be wrong? Below are photos of the deck I stained in July 2023 and what it looks like now (September 2023). I have also attached a pic of what the stain looks like under my recycling boxes compared to the other.
It could be dirt stuck to the stain from your area or mildew. Redo the prep and stain and then try the RAD Guard after the stain dries.
HI, Is it possible that splatter from a bluestone stoop is causing staining on a douglas fir porch? The deck was treated with penofin. The splatter marks come after heavy rain. The porch is covered.
Sorry but no idea but definitely coming from something else.
Hi I just stained my new deck waited one year before doing so, I used the cleaner and brightener first then one coat of stain, then it did rain hours later which was not suppose to, but a small part of my deck is a little darker than the rest, should I put another coat on the part that is lighter so it will match? It really did turn out good but now I’m not happy with the look since one part is little darker.
More is not better and it may not take another coat so leave as is.
We just had a fir tongue in groove porch floor installed. It was stained & sealed with Ready Seal and looked good for 2 weeks. It rained on Thursday night and the deck is black (see attached picture). Our poor builder is ready to rip the floor off and start over. Thank you for any help you can provide.
That looks like rust. Someone got metal in the wood. Could have been from cutting with a metal blade or steel wool, etc. Strip and brighten for prep with Restore A Deck Kits.
Hello, Scott. Thank you for giving us this forum. We are in the process of re-staining our deck. We just finished sanding it using an orbital sander and detail sander. Then we power-washed it and dried it with clean rags, using a bit of pressure while wiping to remove any remaining dirt. Would you recommend that we proceed to stain or should we wash the deck with a deck cleaner then follow with a wood brightener? This is our first time doing this so we want to do get it right. I’ve attached a couple of pictures for you. Thanks in advance for your input! We really appreciate it!!!
The wood looks very smooth. What grit of paper did you sand with? Does water bead on the surface or soak in right away?
We used 80 grit. I just poured a drop of water and it beaded on the surface.
The stain will not take then. You may have to let it sit for 1-2 months and then clean and brighten for the prep.
Thanks, Scott. I tried staining in an inconspicuous area and it looks like it took the stain provided that I applied with a brush (back and forth motion) then wiped off the excess with a clean cloth. Do you think I should still wait a couple of months? Can I try staining it now and if it doesn’t last, clean and brighten in a few months then re-apply the stain? Thanks again for your input. This forum is really helpful.
The easiest thing to do is just wait until Fall, prep, then stain with one coat. We would not do it now.
Thanks, Scott! I will do that. Have a good rest of your week.
Thanks!
Hi, I found your site too late it seems. I heavily pressure washed my deck to strip off the old stain. In the process I damaged the surface slightly in few places. I belt sanding most of the rough spots. It seems to me my deck is very clean now and most boards look bright, but I have a few darker boards standing out. These have move cracks and have a slight bulge. Can you tell from my photos whats up with these dark boards ? I plan to put Flood solid stain (light color). Since I heavily pressure washed my deck, do I still need to use a cleaning solution and/or a brightener ? Thank you so much and thanks for your informative site.
If using a solid stain you do not have to worry about the boards being darker or lighter in spots.
I see you recommend a brightener. Do i need a brightener in my case of ‘over’ pressure washing ?
No need when using a solid stain in this case.
Thank You!
I used Penofin Step#2 and pressure washed our Tigerwood deck and oiled with Penofin Hardware Oil Natural. After seeing my deck turn black I am thinking I need to completely re-clean and start over, but obviously not using Penofin products. I will state that not all of my wood had original color prior to oiling so maybe I needed to use more cleaner? However, even on the wood that was very clean and dry turned dark. Can you please provide me steps I need to take and best product to use? I wish I would have found this site prior to starting. Thank you! Not sure my photos attached.
You need to strip and brighten for prep. Once removed, try Restore A Deck Stain in Light Walnut color. Use the Restore A Deck Stripper/Brightener kits for the prep:
https://www.deckstainhelp.com/restore-a-deck-injectable-deck-stain-stripper-review/
Why is my decking looking this is. I have now used red label to strip the Ron seal deck stain off. It was put down last year and just looks dirty all the time.
Post some pictures.
We have Penofin red label on our deck for 3 years. It has darkened the most where exposed to the sun. We don’t want another coating of the Penofin. What can we use instead?
Thank you!
PS We don’t want to sand the deck.
Strip and brighten for prep with Restore a Deck Kits and then stain with Restore A Deck Stain or TWP stains.
Help! I have this big mark on the deck next to the wheel… The rest is grease marks from a bbq, not sure if this is the same or something more suspect?
It will not fully come out, too deep in the wood.
Do you think that all of it is grease stain?
Mostly grease, possibly some burn.
Can the moisture causing the blacking of the deck be underneath the deck? Lack of air flow under it?
Doubt it but if really bad and it is rotting from the bottom up, then yes you could have an internal darkening from the rotting damage. Rarely have we seen this though.
I have installed red cedar clap boards with the rough side exposed some 15 years ago on my house. I applied Penofin Ultimate Premium Western Red Cedar oil stain shortly after installation and reapplied the stain over time. The cedar clap boards did turn black. I prefer not to go through the process of the stripping process before reapplying more stain. Can I use TWP (oil) 1500 Redwood to the already Penofin stained clapboards to lighten the color? I am also concerned that the two products are not compatible. Thank you
No, you have no choice to remove the Penofin by stripping before using any other semi-transparent stain. Use the RAD stripper kits: https://www.deckstainhelp.com/restore-a-deck-injectable-deck-stain-stripper-review/
Hi i was reading up Penofin stain. So you guys dont recommend them anymore? I lice in Canada and TWP, AC and Defy do not have a dealer here. We do however have Penofin. If you dont recommend Penofin, what orher products can we use aside from above mentioned product. I understand we will most likely need to re-do the sealing more often. Thanks.
We stopped using Penofin the early 90s due to their issues with the stain darkening and turning black. Plus it smells really bad. Ordering the TWP or AC from the states is your best option if you cannot find them locally.
older redwood deck use oil or water base stain
Does not matter as long as you prep correctly and use a quality stain: https://www.deckstainhelp.com/the-5-best-deck-stain-reviews-and-ratings/
I had my pressure treated wood deck repaired, cleaned, and stained a few months ago. Now many areas are black. Did the company I hired do something wrong? Anything we can do?
Thanks!
No, it is not their fault. Looks like leaf stains, dirt, mildew, etc.
Thanks! Normal for stains and mildew so soon after staining? How can we remove without harming the deck?
Is it normal for stains, mildew, etc so soon after staining? What is best option for cleaning without damaging wood or stain? Thanks!
You cannot prevent stains from leaves decomposing unless you remove the leaves right away. Mildew can happen no matter what if in a wet environment. You cannot just remove the dirt, stains, etc, and not harm the deck stain finish at the same time.
I have black dots over half of a brand new cedar floating dock for I built for our pond … it’s been in my garage since Mother’s Day I just pushed it out Friday July 17th, it rained on it Sunday, Monday morning black specks all over half the deck… it has not been stained or treated with anything….is it mildew?? I tried power washing it out with no luck it sanded out a little but not easily. What can I use to remove the specks??
Thanks Michael M
It is mildew or rust. Bleach removes mildew. A wood brightener removes rust.
I thought I was doing everything right restaining a cedar sided house. It’s originally stained with Penofin Transparent Cedar red label and I am applying the same thing.
The house was last stained probably 5 years ago, working on the south facing side, the cedar has lots of black or dark patches at the bottom of the vertical cedar siding. The upper 2/3rds is in relatively nice shape still.
My prep-
Using Penofin Cleaner – dissolving in water and applying with a pump sprayer, letting it activate for about 20 minutes and then scrubbing the surfaces, doing a second application on the lower areas that have the blackest staining. Hosing off with garden hose
Using Penofin Brightener – dissolving in water and applying with a pump sprayer, letting it activate for about 20 minutes and then doing a second application on the lower areas that have the blackest staining. I can visually see the dark areas lightening during application. Hosing very thoroughly with power sprayer, making sure not to damage the wood, but enough that some mushy wood fibers are showing up and being washed off during the spraying.
Letting dry 24 hours.
The surfaces look great, much lighter, black staining gone, cedar looks almost brand new.
Reapplying 2 coats of Penofin red label. However, this is where I am having the problem, as soon as I apply the first coat, the darkness at the bottom if the cedar, very ugly seems to reappear. The nice bright even surface is dark again at the bottom as if I never did any prep.
I stopped, only covered a small section with one coat, I don’t want to go any further until I know what steps to take, or is it possible the wood is so old it’s just beyond coming back to like new?
Picture below -shows before, after cleaning, after restaining
Looks internals water stains near the bottom causing the darkening. Nothing you can do about this as far as prep or a different stain brand.
Hi thankjs for the quick reply. I’m confused, what are “internal water stains”?
THanks
Water damage in wood turns black in color and cannot come out. Most likely moisture wicked up from the froof and started to degrade the wood cell structure. It is a permanent discoloration.
Hi,
Sept. 2019, I contacted Rustoleum to report the Deck Restore product, with a limited lifetime warranty that I purchased through Lowe’s, was all peeling off. They first tried to offer an inferior stain to repair the surface. I finally got to David Summers the product manager for Rustoleum. His final offer, after working this issue for months with Rustoleum was to refund the purchase of the product, purchased 8 years ago, if I have the receipts, or they provide a product replacement with no future warranty. I cannot get all the old product off with a pressure washer, and it was too late to apply, as the temperatures are too cold for the product to set. My only option is to replace the deck floor. I asked for Rustoleum to cover material only, and he indicated a limited warranty only covers the Restore Product costs. I am still working this with Rustoleum and wish there was a current class action suit. All I wanted was for them to provide their current similar product for me to cover the deck and extend the warranty for lifetime. They refused.
That does not surprise us. These “extended” warranties are BS and the companies do not back them up.
Hi there. Had brand new deck installed 7 months ago ( treated wood). Read multiple articles on your site and prepared wood with Restore-A- Deck products and then ordered recommended good quality Armstrong Clark wood stain. 3-4 months later noted black residue on the surface of the deck, currently so bad it almost leaves marks on the soles of my feet when walking barefoot. Not even full year and deck has completely different color even though good products were used and followed all instructions to prep and stain. Located in NJ.
I was planning on cleaning the deck in the summer and restaining with TWP instead? Not sure what happened but it looks bad.
If the mildew is on top of the AC stain then it is impossible to prevent. Stains can prevent or stop growth in the stain but no stain can stop or prevent mildew growth on top of the stain. Mildew can grow on any surface. It also could be an issue with pollen. Pollen is a known mildew promoter and that could have fed the growth on top of the AC. It wouldn’t hurt though to switch brands and see if you have fewer issues since you will need to redo anyhow. Try the TWP 1500 Series or Restore-A-Deck Stains.
Hi there. Thanks for all the great advice on this thread. I’ve just had my deck sanded and re-oiled. It was last oiled about a year ago and was definitely ready. They sanded and applied three coats in one day, and now checking it the next day there are lots of black marks in the wood. Could you advise on what this is from and how to fix it? The wood is Ipe. Thank you!
It looks like burn marks in the wood from the sanding. Not any easy fix. You would have to strip and then resand all property. Brighten the wood after.
Brand new cedar deck has all these black leopard print like splodges all over it. It appeared after the first rain. No metal sanding as been done anywhere near it. No railings even installed yet! Almost looks burnt in places. This is a professional install.
Any suggestions?!
Definitely, something in the rainwater caused this but not sure what. Hopefully, a good cleaning and brightener will fix this/ See here about new wood: https://www.deckstainhelp.com/staining-a-new-deck/