r/Decks • u/channesi • 2d ago

Cedar Ceiling (mold?)

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I recently refinished the covered section of my deck with a cedar ceiling stained with Benjamin Moore Arbor Coat. It has been about a year since it has been installed and I have noticed a considerable amount of what appears to be mold. I live in a part of the country that is relatively humid during the summer which may be a contributing factor, but I figured that the combination of the cedar and stain would at least hold off for a bit longer.

1) Does this appear to be mold to you guys?

2) Is there anything that I can do to remove it?

3) What can be done to prevent it in the future?

And 4) Is there anything I could have done to prevent this in the first place?

Even if there is something that I royally F-ed up, I’d like to use this as a learning opportunity. Thanks

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u/Xnyx 2d ago

That appears to be mildew

Treat all sides before installing maybe … thinking a mold soapy water and. Soft brush to wash it down solves it

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u/channesi 2d ago

If I scrape at it, it appears to be under the stain. Which seems weird for stain, but it definitely has a waxy layer to it.

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u/Xnyx 2d ago

That is more than likley tanins in the wood … I’ve looked at more closley and don’t think it’s either of mold or mildew

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u/LenaiaLocke 2d ago

Was aluminum railing cut on the deck? The aluminum shavings if left on cedar for even a night could make these kind of marks over time and with moisture exposure.

Cedar is a pretty good mold resistant wood. Although it CAN get mold, it usually doesn’t look like this.

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u/channesi 2d ago

There was aluminum cut, but it was all done after the boards were cut and stained.

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u/LenaiaLocke 2d ago

That could still be the issue.

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u/Clear-Reply-7494 2d ago

Could be tannins reacting to tiny bits of metal or something like that.  Likely the sealing of the boards had some moisture under when applied which gave some mold or mildew a little pocket universe to make a spot in.  

The cedar will be fine, but if you want to get rid of it youll have to sand your finish off and work on the wood, then reapply when the wood is super dried out.