Help!! What is that on my new deck?

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.

Attached Thumbnails http://www.renovateforum.com/attachm...deck-deck1.jpg http://www.renovateforum.com/attachm...deck-deck2.jpg http://www.renovateforum.com/attachm...deck-deck3.jpg



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