The characterization, analysis and interpretation of historic mortars ("mortar analysis") constitutes a tool which is useful both in understanding how a building has been constructed and also in making recommendations for repointing.
Mortar analysis can be completed with a variety of test procedures. Test protocols, ranging from the simple and inexact to the precise and complex include:
For projects within which the primary objective is to gain an understanding about the types of materials which may have been used to point a building and to make recommendations for repointing, the calcimeter test protocol is used. Mortar samples are procured by an experienced conservator who can make observations about the type and condition of the surrounding masonry. Samples are then analyzed, and basic compositional characteristics determined by an assessment of reactive properties (measuring the amount of gas produced during reaction with hudrochloric acid). Color, relative hardness and porosity - all of which are markers for different tyoes of binders - are also assessed. Replication mortars are then produced.
It is not always necessary or advisable to exactly match the composition of an historic mortar. As such, our conservators sometimes recommend alternate mixes which match important visual characteristics such as color and texture, but which will also perform adequately within the larger context of the surrounding masonry system.
For projects which require a higher level of study, Keystone partners with colleagues to provide petrographic analysis, and with independent testing laboratories to complete elemental and microstructural analysis.