Highbridge

The arrows indicate fine-grained crushed limestone used as a plasticizer in this masonry cement mortar. The job specification calls for a cement-lime mortar mixed by proportion and the examined mortar is determined to be noncompliant. It is important to identify components such as these before performing a chemical analysis. It would not be possible to estimate the original proportions without knowing to which component each chemical element is attributed.

A Highbridge chemist vacuum filters several dissolved mortar samples. Through a series of chemical digestions, the binder components are brought into solution leaving the aggregate retained in the Buchner funnels. These solutions are then brought to volume and aliquots taken so that each major element may be measured independently through atomic absorption spectroscopy. These measured elements are then mathematically partitioned into each binder component identified petrographically in order to reverse engineer the original mortar or stucco design.

Mortar and Stucco Analysis

Unlike concrete, compressive strength is generally a less critical property of masonry mortar or exterior stucco. Workability, water retention, elasticity, and bonding performance are significantly more important and are usually governed by the appropriate proportioning of constituents and qualities of sand gradations. Mortar or stucco analysis is performed through a combination of petrographic and chemical analysis with the goal to estimate the original mix proportions and assess the qualitative characteristics of the final product. Petrography is used to identify the various individual components and can easily distinguish between cement-lime blends and masonry cements as an example. Through thin section analysis, characteristics of the hardened binder such as degree of hydration and relative original water contents may be investigated. Quantification of the mix follows through a chemical analysis using atomic absorption spectroscopy along with several wet chemical methods. The techniques used are in accordance with ASTM C 1324.

Highbridge is perhaps best known for its work on historic mortar and binders. For more information on our application of petrography and chemistry to preservation projects, please visit our Historic Preservation section where you will also find a discussion on historic mortar analysis.