New decking mould/mildew

[Iain741]

Hi all,

I built decking in my back garden last summer and just over the last couple of months I’ve noticed a bit of a mould/mildew appearing on some of it.

The boards were all pressure treated and I used cut end protector on anything I cut. The main deck itself has a decent run on it and doesn’t suffer standing water at all. The affected areas get sun in the afternoon (if there's any to be had!), so it's like it's in a damp & dingy spot.

I've attached a few photos.

Does anyone have an idea what could be up there? And what, if anything, I could do to treat it?

Cheers!

 

[JohnD]

they don't look like they have been treated with a water-repellent stain or oil.

 

[Iain741]

Hi, no they haven't been oiled/stained.

I thought pressure treated timber shouldn't required it, for the first few years at least (unless for appearance sake). Maybe that's not the case?