Black marks on the new outdoor setting

[nabs]

Thanks for the advice on finishing the deck Have ordered Spa'n Deck Next weeks job to do the finishing!!!
We bought a lovely hardwood setting to use on the the deck, and it has been delivered. It has been on the deck for three weeks and is getting some horrible black marks .It is made locally from locally milled timber - not sure what the timber is, and we have asked the manufacturer to return and fix it but are wondering what causes these black marks.
The setting was oiled with Wattyl deck oil prior to delivery so it was bought ready to use. It hasn't had anything spilt on it. There are no trees adjacent to the setting.

[nabs]

Footnote - the decking also has the black marks on them.

[ozwinner]

By the looks of it, it wasnt seasoned timber thats why it is cracking, the black is the tannin being released from the green timber.

Al

[Larry McCully]

This is caused by a electrolysis reaction between Tannin acid and metal. During the sanding process, small deposits of metal grit get lodged in the open grain. In a short period of time ,the tannin acid reacts with and metal and stains that infected area. It is common when new decks are built and iron fillings from roof works are on the deck. It is more common with eucalypti spices. The piece needs to be washed with a deck cleaner that contains oxalic acid.