Clean a lovely Cotswold retirement village.  All is well, newly built when i started 5 years ago.  Lovley pvc windows and beautiful stone sills.  5 years on and the sills are as the picture shows, a car crash.  Moss, mould, black spot, lichen etc etc.  its 3 stories high and they have asked if i can clean the sills.  Don’t want to say no as I don’t want to say no.  Just been on FWC ISOH health and safety course as a necessity to comply and come off safe contractor scheme.  This has slowed my recklessness down.  Anyone been asked to complete a similar stone sill job.  Thinking, hypo, jet wash, biocide, but any experience of such a sill clean will be appreciated