The restoration, rehabilitation, and adaptive reuse of existing structures increasingly are dominating the construction industry. The Secretary of the Interior's Standards for Rehabilitation of Historic Buildings and many local historic preservation codes require that when exterior restoration work is being planned, original pointing and construction mortars be tested to determine their original constituent materials, both for the purpose of performance specification and for the purpose of matching the original appearance of the mortars. Even without the regulatory impetus, it is wise practice to test existing mortars to determine their properties and behavioral characteristics. Currently, no ASTM standard exists for testing historic mortars.
Developing a standard is not without some difficulty. Current standards for concrete testing, often applied to the testing of historic mortars, are based on the assumption that the material to be tested is cementitious and has a limited range of components. Historic mortars have far greater range and may or may not include river bed or clayey sands, natural or synthetic hydraulic cements, and prehydrated or site-slaked limes. More exotic additives include coal dust, brick dust, ground calcareous stone, and animal blood. The paper explores a number of approaches to analyzing historic mortars, including quantitative and qualitative physical and chemical testing, empirical observation, and the importance of historical data in evaluating historic mortars.