[Mike Halliday]

Did this job yesturday and although the customer was happy they were concerned with the brown staining that they didn't know was under the dirt, I explained I believed it was staining  from ferrous sulphate  used in moss killer which they had applied to their lawn. Do you agree? Can it be removed?

[Smurf]

Mike why did you not treat it with hypo as those chepo concreate slabs still looks dirty to me?

[Mike Halliday]

[the king]

i have to also agree there they dont look clean  i wound be disappointed with that result if that was me yeaaaaahaa 

[robbo333]

I had a window cleaning customer who had exactly the same. He said the gardener had put weedkiller down and spilt some on his slabs. The slabs were immaculate. Just for the hell of it, I tried a fairly weak hypo and wire brush, didn't even touch it.

[chris scott]

Yep...its staining from moss killer. Do you want me to quote for removeing it?

[chris scott]

The Singer will leave marks too....its cast iron.

[Mike Halliday]

Yep...its staining from moss killer. Do you want me to quote for removeing it?

No need I'm going to order some Monty solution and use that or I could use an acidic solution.

But in reality   they are not too bothered and are overall very pleased with the clean so will leave it, I just was asking out of professional interest

[Smurf]

https://www.owatroldirect.co.uk/product/net-trol/
Not just for wood either https://www.youtube.com/watch?v=n2_RrLTGeBY

[Kev Martin]

If your satisfied with half a job leave it!  If not Pre wet it with water then apply Miracle Heavy Duty Cleaner (Acid Substitute) Scrub it in with a Mono Rotary and extract, possibly add some Honing powder if required, rinse and it's done!