Even stone can deteriorate. Stone and other similar construction material is subject to the same harmful effects of weather and other environment concerns that can compromise wood and alternative composite building materials. While we expect wood to degrade/decay over time there is most often the false sense that stone will last forever. Obviously stone is far more durable than other siding and construction materials, however, regular maintenance is still required. Stone facades are especially vulnerable to the elements. Although moderate exposure to rainwater is clearly unavoidable and is beneficial in cleaning the exterior surface of the stone it is responsible for the majority of stone damage and most often attributable to cycles of heavy saturation and drying. Reasons for these cycles vary from home to home but are usually seasonal weather factors, leaking or insufficient gutter systems, ineffective cornices, blocked drains and clinging vegetation.
The most common causes of stone deterioration include:
The freeze and thaw cycle. This cycle is very well known to us here in New Hampshire and Maine. Through capillary action water is drawn deep into the stone. This process causes a mechanical stress on the porous walls upon freezing. Cracking and separation are the readily apparent signs of damage.
Salt crystallization. Soluble salts are drawn in the pore network with water where the form crystals within those pores. Since the salt crystals take up more space than when in solution their expansion causes structural damage to the internal structure of the stone. The telltale sign in this case would be the formation of efflorescence (salt deposits) on the materials surface.
Acidic action. The more common method of transferring an acid to the surface of the stone is through acid rain. Acids that are deposited on the stone will, over time, dissolve the stone. The result is a roughening of the surface or in the case of some stone, an actual separation of its component layers.
Vegetation. Excessive vegetation in close proximity to the stone as well as moss and vines trap moisture in the stone and severely restrict the process of evaporation. The heaviest damage is caused by the root structures of the vegetation that over time and through mechanical action dislodge mortar and open joints between the stonework.
Structural movement. In cases of moderate to radical settling or upheaval even sound stone can be compromised under the additional stresses. Those areas most often affected are lintels, sills, doorways and windows. When this occurrence is combined with any of the above conditions the affect of the movement can be dramatically increased.
Unlike death and taxes, stone is not forever!