Deterioration and Restoration of Plaster, Concrete and Mortar

This paper discusses plaster, concrete and mortar in terms of their chemical composition, reviews the deterioration of these materials and suggests possible conservation treatments for them. In terms of chemical components, plaster is considered in this paper as being formed primarily of calcium carbonate or calcium sulfate dihydrate (or a mixture of the two); concrete as primarily a mixture of calcium silicates and aluminates; and most mortar as a mixture of calcium carbonate and concrete. It should be remembered that minor constituents and impurities, whether introduced in the original preparation of a material or added in some later treatment, can significantly affect the deterioration process. In addition, the physical structure of a material significantly influences its resistance to deterioration. A notable example of this type of influence is the effect of air-filled voids in concrete, which can either increase or decrease the concrete's resistance to frost damage, depending on their nature and distribution.