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Basic Mortar Analysis
HP 306 Lab Assignments

Goals:

The goals of this procedure are to determine three common components of an historic mortar: (1) the binder (typically acid-soluble calcium carbonate CaCo3), (2) the fines (pigments and impurities such as clays and aluminates); and (3) the sand or aggregate. This procedure uses acid digestion, filtration and microscopic analysis of the fines and aggregate.

Intent and limitations:

While this procedure may work reasonable well for characterizing mortars for much preservation work, there are two major limitations. First, this is not suitable for calcareous mortars that use limestone, shell, or coral sands, as these aggregates will dissolve in the acid. Second, the procedure is not suitable for determining the amount of cement that may be in a mortar. Thus for hard cement mortars that cannot be easily crumbled with fingers, a calcimeter analysis would be necessary to determine the amounts of soluble silicates present.

Equipment: analytical balance (0.01g precision), mortar and pestle, 250 ml beakers, 250 ml Erlenmeyer flasks, funnels, filter paper (417 coarse & 413 fine), 14% muriatic acid (or 15% HCl, or if lime mortar, 5% distilled white vinegar), water, drying oven / microwave oven, microscope, sieve set with U.S. Standard sieve numbers: 4, 8, 16, 30, 50, 100, 200.

Procedure:

1. Sampling

2. Sample preparation

3. Acid digestion

4. Microscopic analysis

5. Sieving

6. Report

Copyright. Prof. Thomas Visser, University of Vermont Historic Preservation Program