Why is my new pine fence turning black? Can I stain right over it without creating a bigger future headache?

Question

We put in a new pine fence about 2-3 months ago.
(Southern Yellow Pine, from Lowes. They called it “Severe Weather Pressure Treated Pine”)
I have been trying to stain/seal it for the past month and a half but we have had one of the wettest summers on record. And when it’s not raining, it’s 100 degrees and 30000% humidity.
Over the past 2 weeks the panels have rapidly started turning grey/black. I don’t think the sun ever directly hits this side of the fence so I assumed it is mold..?

Based on the picture and info, is my assumption correct?

If so, do I now have to remediate the mold by doing the whole bleach scrub and dry process?

If I don’t do the bleach scrub and just stain right over it, will I be creating a recipe for disaster or just end up with a sub-par looking stain job?

Ed Beal · Answer

That is natural aging , the most rot resistant wood redwood turns gray within 5 years , cedar within 3 and that’s in Oregon.
If you stain it a color or paint it it will hide the aging but this is normal with most any wool product, pressure treating keeps it from rotting not aging.

greengecko · Answer

I was thinking it could be algae, but the discoloration looks relatively uniform across specific boards so it's likely natural aging as mentioned. Rooves get dark streaks from algae like the second picture in that link.

Answered by greengecko on February 6, 2021

Why is my new pine fence turning black? Can I stain right over it without creating a bigger future headache?

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