How do you clean stone window sills.?

[Eddie dragon]

First request for this so clueless. After ideas best chemicals and an idea of how mutch to charge. Big white stone sills. I don't do soft washing, mentioned it to the customer as possibility. They don't won't the brick work cleaning just the sills. 

How would I best stop drips from top sills in particular. Walls are realy realy dirty brick so any run will stand out a mile. 

Should have got photos I know. Sills are pitted chiped over painted concrete.

Isue is yellow lichens. And Alge in the deeper pits and cracks. 15 of them from 3-8 feet long. 

No idea what to charge as don't know how long it will take. 

 

[Cristian]

For this job you need Meta Clear, you brush this stuff on then wash it off.