01
Correct the conditions first
Shade, overhanging vegetation, poor drainage and persistent dampness encourage growth. Trim vegetation where appropriate and keep gutters and valleys clear.
02
Avoid destructive cleaning
High-pressure washing can drive water beneath laps and erode or break slate. Wire brushing and unapproved chemicals may damage stone, metals, masonry and landscaping.
03
Use a conservation-minded plan
Determine whether cleaning is necessary for performance or mainly cosmetic. Test the least aggressive compatible method in a small area and use safe roof access.