Solid stone – surface damage or deterioration

Cause

Air-borne pollution, dust or dirt combined with rain causing acid attack on the stone – particularly susceptible are limestone and Oamaru stone

Repair

  • if damage is severe or the appearance is unacceptable, contact the stone supplier for advice. Restoration of acid-damaged stone surfaces is possible but is best done by experts
  • be aware that many stones are porous, and preventing damage or staining in the first place is a better idea than trying to clean or repair it after it has happened
  • house and gutter design and maintenance must ensure that there are no localised high-level flows of rainwater being chanelled down any stone surface. Over time this can result in damage or staining that can be impossible to clean away
  • stone walls should be washed once a year with water and mild detergent using a sponge or soft-bristled brush. A low-pressure garden hose can remove any detergent residue. Don't use chemicals, abrasive cleaners, hard brushes or high-pressure water blasters as they can potentially damage the stone surface

Cause

Oxidation of impurities in the stone

Repair

  • as for the first repair above