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