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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..?

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

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

  3. 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?

enter image description here

  • You used the pressure-treated tag, why ? What kind of wood are the posts? Curious as to why Pine and not a more weather resistant wood, cedar, redwood etc.? – Alaska Man Aug 14 at 19:51
  • They’re Southern Yellow Pine. It was all we could afford unfortunately. They were only $50 per section from Lowes. They called it “Severe Weather Pressure Treated Pine” – user2831690 Aug 14 at 20:04
  • Thanks, “Severe Weather Pressure Treated Pine” - All of the wood or just the posts? I added the pertinent info to your question, You can use the edit button to add or modify as necessary. – Alaska Man Aug 14 at 20:14
  • pine doesn't stain well and neither does PT, it generally looks splotchy and amateurish even under the best conditions. You don't want to seal the fence either, that's more to resist standing water like on a deck, but used vertical, it can slow the natural wetting and drying out of the wood, causing splitting, rotting, and un-even gaps. – dandavis Aug 14 at 20:55
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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.

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  • Awesome thank you so much. Initially I assumed it was simply aging as it was kind of my indicator that it had officially ‘dried out’. I started getting worried because in the last 3 days the color went from 1-3 discolored panels to 20+ panels And we had just received after receiving 4” of rain and tropical humidity so we were drenched for days and I started to fear mold. Glad that is not the case. Looks like I’ll start staining/sealing tomorrow FINALLY . Thanks again! – user2831690 Aug 14 at 22:54
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    I remember having this happen to my first deck years and years ago. All the sealers that guaranteed to keep the deck looking new never stopped the gray.+1 – JACK Sep 16 at 12:00
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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.

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  • What does a link to roofing have to do with a fence? If there's a specific image that you want to have referenced, please edit your post then click the "sun-and-mountain" icon and paste in the link to the specific image you're after (include the URL in the text of your answer as an image source - that's expected here). The system has flagged this answer as potential spam, and I'm finding it hard to disagree. – FreeMan Sep 16 at 16:23

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