Do I need to use any chemical when pressure-washing slimy concrete yard?

[d000hg]

I've now got my Nilfisk pressure washer (thanks to the forum for the recommendations). One job I have is to clean my medium-sized concrete yard. It's dirty and stained but in some places is outright dangerous when damp... it's like black ice and I've nearly fallen several times.

I expect the high pressure jet to scour the slime away - I should use the jet not the special patio attachment right?

Is it worth getting any chemical to stick in the bottle - cleaner or poison - or not for this task?

 

[Burnerman]

Use the full power pressure nozzle first......that should clear the crap away, and keep it like that for a few months. If it's a non ventilated area, the moss will return in due course.
John

 

[d000hg]

Yeah... mostly it's quite open with a few problem spots. Looks like it hasn't been done for a while and has built up - plus under some large trees so while it's ventilated there is constant leaf drop and so on, which will compost if not kept tidy.

Thanks.

 

[ellal]

Hope you are enjoying your Nilfisk d000hg!

As regards the 'problem spots', can I recommend this cleaner: https://www.toolstation.com/shop/p84539?table=no

Pressure wash the worst off and allow to dry before application.

Did a trial on a very stubborn oil stain on block paving (brush on), and it says leave it on for a maximum of 5 minutes before washing off.

Thought I'd leave it on for 10 minutes as I had previously had no luck shifting the stain - it took the blocks right back to original which now look too good for the rest of the drive!

I then used it on dirty concrete and patio slabs (but only left it on for a few minutes) before pressure washing and it came up a treat.

More tricky to use than an 'add in' as you can only do a small area at a time (brush or roller on), but in my experience a much better result.

As I found out though, make sure you do test a small area first.