Black Spots Suddenly Appearing All Over Ipe Deck! - General DIY Discussions - DIY Chatroom Home Improvement Forum

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Old 08-11-2012, 02:36 PM   #1
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Black spots suddenly appearing all over ipe deck!

We had an ipe deck installed last month. It's on the south side of our home and in bright sun for most of the day - in fact, the color has already faded considerably (we haven't oiled/stained it yet).

Currently, our contractor is building a pergola over the deck. The pergola framing is all pressure-treated pine. Two days ago, there was a lot of trimming of the PT going on, and PT sawdust blew all over our deck. Yesterday, we had a lot of rainfall. Today, there are black spots ALL over the deck - and one particular area is especially bad - just under one of our 4x4 PT posts that had been trimmed.

Here's a close-up photo of the ipe decking with black spots:

Mild washing nor sanding seems to remove the spots. I can't imagine that mold/mildew could appear so suddenly over such a large area. Is it possible that the chemical sawdust from the pressure-treated wood + rainfall created a corrosive situation for my unfinished ipe decking? Any ideas on how to remove the staining? Also, our contractor was trimmed off the extra-long metal lags on our doubled 2x12 PT beams over the deck - is it possible that there was some sort of dust produced by this, that may have stained our deck?



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Old 08-11-2012, 02:59 PM   #2
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Artillery fungus?


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Old 08-11-2012, 03:33 PM   #3
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I googled images of artillery fungus - I don't think it's that, but thanks for the suggestion.

Here are some more photos. It's just so strange that it seemed to have happened overnight, and just after a lot of construction work above the deck.

In this photo, just under the water table, you can see a particularly bad area and also a streak right next to a 4x4 PT post (upper right corner of image):

The PT post and a streak of mystery black stain on the ipe:

A close-up - you can see how much our boards are checking, too:

And here's what the whole deck looks like with the pergola (to be trimmed out in Azek) under construction:

I'm going to see if some oxalic acid wash helps - I'll test it on an inconspicuous spot. I'd really love to know what is causing this - mold/mildew, something inside the wood, or some reaction to PT sawdust.

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Old 08-11-2012, 03:48 PM   #4
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I built an ipe deck very similar to yours, maybe a bit larger. I believe the spots you are looking at are intrinsic to ipe, since my deck has some boards with similar discoloration. Ipe is quite oily, and my guess is that the oil oxidizes to a darker color over time. When I first built the deck, I used special oil on it to keep the reddish color, but after a year I decided it was not worth it to keep oiling it, and it has begun to go silver on me, which hides most of the dark spots and lines. You may want to consider a similar approach, as no amount of oiling is going to make the darker lines in the ipe get redder like the original wood. As to the use of oxalic acid to bleach the spots, let me know how that works, I am curious.
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Old 08-11-2012, 05:58 PM   #5
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I and others have posted on this topic and situation before. Any chance you fertilized the yard recently? Could be spots from metal in the fertilizer. Things like iron sulfate will stain badly.

Even in other formulations, people do not realize the fertilizer companies can stick a large percentage of just about anything in fertilizer sacks under inert ingredient labeling laws without having to disclose it. High tech waste metal like chrome, cobalt and iron can get in and ultimate into your piece of the environment.

Or you could be picking up tiny metal fragments from elsewhere in your environment. Metal fragments from shot nails or deck screws? Saw blades or abrasives? In the posts on the topic there were some other obvious sources of metal fragments that I cannot remember. Try searching this site.

Last edited by user1007; 08-11-2012 at 06:01 PM.
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Old 08-11-2012, 06:31 PM   #6
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He used 4 X 4's for the post, oh boy.

If it happened over night then I'd bet it it is iron from the cutting of the bolts.
Chips left on the deck over night will surely rust.
I know for a fact just leaving a nail or paint can sitting on a deck can cause stains.


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