How I got Rid of Leaf and Pine Needle Stains on a Deck

This picture shows the hieroglyphic-like stains on the deck, together with a part of the deck where TSP and some scrubbing had removed some of the deck stain along with the black stains.

You may recall that I have a brother who comes up with some very unusual finish problems. This one’s a beauty.

As with many people, my brother has a deck attached to his house. The house is located in the Northwest, and last winter the snow remained on the ground for three months. When it had melted off, the deck, which had been finished with a deck stain, was decorated with black stains in the shapes of leaves and pine needles. How to remove the stains without also having to remove, and then replace, the deck stain itself?

Someone told my brother to use TSP, which he tried but found that he had to do a lot of scrubbing and the scrubbing removed a lot of the deck stain along with the unwanted stains.

I suggested that he ask around at paint stores for a solution because it was unlikely that he was the only person in the area with this problem. Lots of people have decks and the winter was equally severe for everyone. He couldn’t find anyone who had experienced the same problem. Really strange.

I have no explanation for his deck being the only one, or for it being so difficult to remove the stains. Neither makes any sense. It’s like the particular deck stain used was somehow involved, that it was somehow unique. (It had been applied before he bought the house.)

Anyway, I’ve found over the years that there are lots of finish problems that seem to have no explanation. The only thing to do in these situations is try to correct the problem – in this case, figure out a way to remove the unwanted stains without worrying about what caused them. And to do this with the least amount of work, which, in this case meant not removing the existing deck stain itself.

As it happened, I was planning a visit this summer so I would have the opportunity to see the unwanted stains myself.

When I walked out onto the deck, I was surprised. The bad stains were not ugly at all. When looking at the entire deck, I thought the stains were beautiful. It was like someone had gone to a lot of pains to paint hieroglyphics all over the deck. Others agreed with me. Leave the stains alone. They were unique.

But my brother was still bothered by them. So we wanted to try something to remove them besides TSP, which hadn’t worked well. We hypothesized that the cause of the stains was mold from the leaves and pine needles being kept damp for three months under the snow. Many deck cleaners contain chlorine bleach, which removes these stains.

We bought a chlorine (sodium-hypochlorite) based deck cleaner, which, in fact, claimed to remove mold and mildew, and to my surprise, it worked almost perfectly without removing the deck stain underneath. That had been my concern, that it would remove the deck stain.

We chose a small out-of-the-way area to experiment with the deck cleaner. It worked well on the right side of this picture.

So problem solved. The issue was now for my brother to decide whether to leave the hieroglyphics or remove them.

– Bob Flexner

2 thoughts on “How I got Rid of Leaf and Pine Needle Stains on a Deck

  1. Sullivans Papa

    Here is Chicagoland, Illinois we can’t buy the real TSP, we can buy TSP substitutes
    re: TSP is still sold and used as a cleaning agent but since the late 1960s its use has diminished in the United States and many other parts of the world because, like many phosphate-based cleaners, it is known to cause extensive eutrophication of lakes and rivers once it enters a water system.[8] Substitutes are generally not as effective.[9]
    Credit: Wikipedia.

    1. Bob FlexnerBob Flexner Post author

      I agree. But my experience has been that the substitutes are still marketed as TSP. Sometimes even labeled TSP or something similar when they are not.

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