On recommendation from some "geezers" who I had in last year to sort out the back patio etc, I used an acid on the front slabs earlier this year. I used a garden sprayer to apply it and hosed it off an hour or so later (may have been longer, I don't remember).
It was OK but in the end I pressure washed it too. Maybe not required if I'd left it longer...
I got the stuff (actually 14% sodium hypochlorite) from eBay and the containers are those black fairly rigid ones - bought 2 x 5l - with hazard warnings all over and a warning not to let the stuff into the water course. I did dilute it quite a bit (6:1 IIRC) as per internet guidance. I suppose thinking about it, it will have ended up in the water course, but extremely diluted by the time I'd hosed it off.
I'll probably finish using it next year but wil lbe back to e the pressure washer after that.
PS Are you trying to keep them in or out? :-)
|
Cleaner for a dwarf wall. 
Cleaner for a dwarf wall. 