Outdoor | stoneconservation

Outdoor Agents

It is difficult to protect stone kept, stored, or exhibited outdoors from agents of deterioration. Still susceptible to the indoor dangers, outdoor stone requires additional conservation considerations to limit the effects of weather and other natural agents of deterioration.

Water is the biggest threat to the integrity of outdoor stone objects. Penetrating between layers of stone, water can physically separate sedimentary rock profiles. Occasionally it is not the water, but what the water contains that is most damaging, salt will crystalize as water evaporates damaging surfaces and internal structures. Winter temperatures can freeze water, causing it to expand. Ice expansion can cause spalling, splitting, and cracking. Other times, water will damage composite objects, or those made of more than one raw material. Water can cause metal corrosion that will stain and destroy some stone types. Corrosive metals expand, and like ice, will damage the structural integrity of stone. Some metal cleaning materials will also stain stone.

Atmospheric pollutants are another significant factor for outside stone. Various acids can be created in the atmosphere and will damage stone. As water in the atmosphere reacts with carbon dioxide, nitrates, and sulfur it creates pollutant agents that can dissolve certain types of stone. Due to high rates of calcium carbonate, limestone and marble are highly reactive to atmospheric pollutants. Discoloring can also occur from industrial pollution. Wind carrying abrasive particles like sand will slowly wear away stone, impacting surface detail and structural integrity of stone objects.

Biological agents also impact stone deterioration. Bacteria, alga, mosses, and fungi all grow on stone surfaces and cracks. These growths push cracks further apart and retain water, contributing to additional water and atmospheric pollutant damage. Some biological agents will discolor stone, while others like biological waste can actually dissolve some types of stone.