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Deck Stain Turned Black

Stain Turned Black

Stain Turned Black

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 all 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 then 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 on 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.

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14 responses to “Deck Stain Turned Black”

  1. Amy says:

    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?

  2. Dee says:

    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.

      • Dee says:

        Ok will try that was wondering if I am going to need to sand it . ???? Thanks for you help

      • Dee says:

        brightened a second time and cannot tell a lot of difference . Other suggestions

      • Dee says:

        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!

  3. SMac says:

    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.

  4. Rhonda says:

    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.

  5. Sue says:

    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.

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*This is first and foremost a help site from our experience as wood restoration contractors. All stain and prepping manufacturer directions were followed with our reviews and ratings. We offer no guarantee of similar results. Take inconsideration that wood and deck stain results may differ due to prepping procedures, different wood types, exposure to UV radiation, natural weathering, etc.