Causes of deterioration of stone

Deterioration of stone is the loss of its strength, shape and appearance with time. Its main causes are:

1. Rain and moisture: water enters pores, dissolves minerals and causes frost damage and weakening of the stone.
2. Atmospheric gases: CO₂, SO₂ and acid fumes in polluted air form carbonic and sulphuric acids that attack limestone and sandstone (acid rain).
3. Temperature variation: daily and seasonal expansion and contraction cause cracks, particularly in stones made up of different minerals.
4. Frost action: water freezing in the pores expands by about 9% and splits the stone.
5. Wind and abrasion: wind-borne particles wear the surface.
6. Crystallisation of salts: soluble salts in the stone or in the ground water crystallise on the surface and spall the stone.
7. Chemical action: sulphates and chlorides from soil, sea water or mortar react with the stone.
8. Vegetation and organisms: roots, moss, lichens and fungi hold moisture and produce acids that corrode the stone.
9. Poor selection and workmanship: wrong bedding, porous stone, poor dressing or weak mortar.
10. Fire and earthquakes may also crack stone.