Decking grain still green after cleaning

[ChrisZx]

Bit of an odd question really but I'm not sure what to do!

We build the siberian larch deck a couple of years ago - last year we cleaned it with ronseal decking cleaner and reviver and it looked brand new again. This year however quite a few of the boards have stubbornly remained green. It's not like it's algae sitting on the surface - it looks to me like the grain itself is stained green.

Larch decking above - I need to give it another go as I was in a rush and didn't scrub as much as I should have (stuff on the right) - but right now I don't think any amount of scrubbing will get the stuff on the left off.

The tanalised softwood planters around the edge are showing the same thing - we gave them a good scrub the other day with the same ronseal decking cleaner and reviver and overall that look brand new again - except the green stains (clearly we missed a bit at the very bottom of this picture! But you can see it in the boards higher up)

I actually quite like it in a way - but I worry its damaging the wood if it is actually mould/algae. I was planning on oiling the decking for the first time this year, but obviously want to make sure its properly clean first.

Is the green colour after cleaning perfectly normal and expected? Is there anything else I should be doing? Or do I just need to stop whining and scrub harder?

Thanks!

 

[freddiemercurystwin]

I would say scrub harder, whilst I'm not recomending it (though have done it myself in the past), I daresay a pressure washer would have it back to bare wood in no time, just pointing out that it needs a more vigorous cleaning regime.

 

[ChrisZx]

I would say scrub harder, whilst I'm not recomending it (though have done it myself in the past), I daresay a pressure washer would have it back to bare wood in no time, just pointing out that it needs a more vigorous cleaning regime.

I was using a pressure washer but only really for washing off, didn't have it on a powerful nozzle setting - will give it a go, thanks

 

[freddiemercurystwin]

It's not recomended but I think that's more for if the timber is in poor condition and there is a danger of blasting it to bits, just hold the nozzle close enough to remove the dirt but no closer.

 

[big-all]

could be wrong but to me they look like deep grained possibly blue mold so not on the surface butt as i say could be wrong ??

 

[ChrisZx]

could be wrong but to me they look like deep grained possibly blue mold so not on the surface butt as i say could be wrong ??

It certainly seems to me like it's not sitting on the surface but is ingrained - will have to look up what blue mould is!

They say larch doesn't need treating with a preservative but wonder if I should try anyway to see if it helps kill this...not sure if that would help or not though

 

[Mike13]

oxalic acid might kill the mould? caution though, it is quite toxic for people and pets