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My Deck Stain Turned Black

Moldy Deck

BlackĀ  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.
Another 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 stain 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.

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4 responses to “My Deck Stain Turned Black”

  1. RJH says:

    have vertical pine vegas on exterior of southwestern home now have black streaks tried dilute clorox with some improvement. what should I do before re staining. should I use the deck cleaners mentioned?

  2. SCM says:

    I had a deck renewed last year. All verticals were in OK shape and were re-stained with a solid stain. All horizontals were replaced with new cedar and stained right away with Flood semi-transparent. A year later the horizontals were black in areas that were exposed to the elements, but still OK under chairs, etc. We tried scrubbing the horizontals with bleach and plastic brushes, which removed the black but also most of the stain (not all). Now it has been mostly unstained for about 3 months waiting for a break in the local rain. A contractor’s suggestion is to sand the horizontals and apply new stain. I’m cautious about using a stripper because I don’t want to remove the solid stain from the verticals, since it still looks great. What combination of sanding, stripping, and/or cleaning do you recommend before applying a new stain to the horizontals? Also, after this process, I’m thinking of using either TWP 100 or Armstrong Clark. Do you prefer one over the other in this case? I’m in central Texas, and the deck gets plenty of sun.

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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.