[drive surgeon]

hi , cold water pressure does not shift some of this black lichen dots, it seems to be in the concrete, on flags especially,   a few customers saythey  use bleach to get rid of them, which is ok on white or grey coloured flags but on coloured flags i just wondered if i used a dilutted mixture of bleach and water would this shift them?   i know they sell some chemicals somwhere for this.  the cold pressure washer does a fantastic job and the customers are always happy but on flags there are usually the black dots left which is a shame,

[Ged]

have you tried a turbo lance on 'em ?

[drive surgeon]

yep!!  it semms to be soaked into the flags!  need chemical i think.

[Rob_Mac]

Drive Surgeon

What is the PSI of the machine you are using and the LPM because we use a diesel pressure washer at 3000psi - 15 lpm and a petrol 4000psi at 12lpm both fitted with turbo nozzles and my slab work is spotless

Rob