[stuartb]

Hi folks,
I'm cleaning a patio which is covered in random small black dots. The patios made from square slabs which are pretty smooth and I think concrete. Should I treat them with SODIUM HYPOCHLORITE to remove the black spotless?  It's about 300 metres so how much SH would I need?
Cheers
Stu

[chris scott]

I use hippo...you only need a bit cause most of it is underwater.

[stuartb]

Mmm...so how much is that?

[Andy_MK]

Ignore Chris, it's not his fault.

I mix 3:1. Apply with a watering can leave for 20 mins then rinse away. Does the job.

If it's stubborn mix it a bit stronger but be very very careful around plants, grass, ponds, streams etc.

Wear gloves, mask and goggles.

[chris scott]

15% NaClO used 1:4  h20. Increasing 1:3 if not working . Clean the surface first with high pressure. Mix with wallpaper paste  or bubbles  (to prevent run off) and apply. Dwell time of around 30 mins. Apply with soft brush . Repeat till you are ecstatic with the results.
Don't spray it ..you will end up damaging something. Keep away from metallic objects ...it's corrosive.

[chris scott]

Sorry I was on the wrong forum  https://www.facebook.com/groups/pressurewashinguk/882687241744469/?notif_t=group_comment_reply   

[stuartb]

Thanks guys. How many metres will a 25th drum clean?

[chris scott]

Hard to say really every job has a different amount of soiling.... Just order yourself  4/5 drums and keep it in the shed for when you need it.... Even "if " you give a £1 per litre of ebay that will make 3 litres of solution ...it's cheap enough.