Hi all,

I have a new deck/pergola built over the last fortnight before the rain came in over the weekend. The deck is tallowood with treated pine stumps and pergola with laserlight covering, and the builder gave it one coat of oil all round before putting it in. Before you know it the black marks/spots appear within a day or two of rain.

Seems to be worst where it was most exposed. Any idea what this may be - mould, sap etc etc ?? And does anyone have any suggestion on how to fix it?

Photos attached of the worst section plus an "emerging" section.

Thanks.

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Oh dear.
I have never used oil on my deck (Spa&Deck for me) but from all reports a single application of oil probably isn't enough. I was under the impression that oil was put down until the wood could no long absorb it and the oil would pool a little on top.

It sure looks like a mould break out. Try some Powerlift or Napisan with a good stiff scrubbing brush.

The link below is from another thread where UteMad had something to say about tallow wood.
http://www.renovateforum.com/f77/cle...tml#post770285

Ummm....Did you do any grinding of metal on or near the deck? Cause that looks like tanin staining from angle grinder metal dust.

If it is, Good luck on getting it off.

__________________
Hooroo.
Regards, Trevor
Grafton

Thanks, I'll give the napisan scrub a go in a week or so when the weather dries up.

Glock40sw: closes thing to it is that we have steel ballustrades put in, but no grinding as far as I now. Will that cause staining?

I had the same problem with a treated pine deck recently.
Was fine until it rained and the whole deck broke out in mold.
I used neat bleach with a mop and it vanished within half an hour.
The treated pine place told be to clean with bleach before oiling,
I think you may have trouble penetrating the oil. let us know how you go.
It might pay to get some professional advice first.

Trever from Grafton might be right, if you left the shavings on the deck and then oiled
the oil may have started the rusting process,a lot of decking oil is water soluble.

I'm with Glock40sw. It looks like metal staining.

Mould would not come up that quickly, and certainly not in such an even pattern, over adjacent boards.


Is it black, and streaking with the grain? If so it will be metal When they cut the metal balusters did they use a grinder? If so all the cuts turn into sparks and dust and rusted with the rain. choice of oil based or water based decking oil makes no real diff, and there in no real solution, other than sanding.

Get the builder back and let him explain.

__________________
Brian

I once used a file to sharpen a steel scraper blade whilst scraping down a wooden boat deck. The next day, after overnight dew, the deck looked exactly the same as that. Rust from the iron filings. Tried oxalic acid, no good. Had no choice but to scrape the whole lot again. I just love working with wood.

Have also seen furniture intentionally stained black using steel wool and vinegar. It looks very similar to your deck, just not as patchy.