Comprehensive ASTM C1324 Mortar Analysis & Historic Masonry Testing Services

Material Testing & Analysis Services

Please refer to our Specifier’s Guide to Mortar Testing for information about specifying the most useful mortar analysis procedures

We have partnered with a nationally renowned testing lab to provide a comprehensive range of advanced masonry mortar testing services, which we supplement with our analysis and replacement recommendations. 

Once the lab has completed the tests and provided a report, we review and analyze the data to identify the original material and make scientifically-based restoration recommendations. In order to make the most accurate restoration recommendations, we’ve run ASTM C-1324 tests on our entire line of historic mortars so we can compare performance characteristics of the original with replacement products and identify the most suitable option.

With the exception of ASTM C-1324, these tests generally have to be performed in some combination in order to yield useful information. We will be happy to work with you to develop the test matrix that best suits your project.

Please allow 3-4 weeks for for most mortar analysis procedures. The lead time may be longer during times of peak demand.

ASTM C-1324 "Analysis of Hardened Masonry Mortar"

One of our most commonly requested tests is ASTM C-1324, which is a comprehensive test of historic masonry mortar. This test calculates the cement to hydrated lime ratios as well as sand to cementitious ratios. The lab test results include a written, photodocumented report with limited interpretation. We will review the test results and analyze them to identify the original material and make restoration recommendations for mortar blending and material matching.

 

ASTM C-1324 Testing

 

This test includes two primary procedures:

Petrographic examination: will be performed on split portions of the sample in accordance with Section 8 of ASTM C1324 to document the mineralogical and physical characteristics of the mortar and describe the mineralogical constituents used in the mortar mixture. Mineralogical constituents usually include aggregate and mineral-based, hydraulic and non-hydraulic constituents of the cementitious binder. The petrographic examination will include the production and examination of petrographic thin sections of representative pieces of provided mortar. Findings of the petrographic examination will provide information that will be referenced and used in the chemical analysis, including mineralogical features in the mortar that may pose potential interferences with the chemical analysis methods, such as acid soluble components in the aggregate that may go into solution upon the chemical digestion of the sample(s).

 

Chemical Analysis: Chemical analysis will be performed on split portions in accordance with procedures and guidance provided in ASTM C1324. Representative portions of each mortar will be ground and chemically digested, then analyzed to determine the concentrations of certain soluble and insoluble constituents. From these findings, and information provided by the petrographic examination, the volume proportions of these constituents are calculated.

X-Ray Diffraction

Phases are identified by mineral names and chemical formulas. Abundance of phases is estimated as “major,” “minor,” or “trace.” Narrative report includes a table of observed phases. XRD on acid insoluble fraction further characterizes the “sand.”

Acid Digestion

Digests the binder away from the sand to determine sand content. If the mortar is very hard and tested by ASTM C-1324, the sand particles may not be able to be kept intact for digestion, thus sand gradation may not be determinable.  Additional digestion of other, larger pieces of the mortar will be necessary to obtain enough intact sand for a sieve analysis. If carbonate sand is present, the sand volume and sieve analysis will be biased. Thin section analysis will be able to assess the approximate percentage of carbonate.

Brief Microscopial Work

Brief microscopial work to examine the aggregates.

Thin Section Analysis

Thin section analysis uses optical microscopy to determine the general composition of the mortar, binder type, and sand types. This analysis will not determine the actual sand gradation or cement to hydrated lime ratios. The lab results include a written, photodocumented report with limited interpretation which we supplement with our recommendations.

X-Ray Fluorescence (XRF)

XRF yields a one-page report listing the percentages of chemical elements expressed as oxides, SiO2, Al2O3, Fe2O3, CaO, MgO, SO3, Na2O, K2O, TiO2, P2O5, SrO, Mn2O3, ZnO, and Cr2O3. Thermogravimetric analysis is used to calculate hydrated lime and carbonation.

This test is useful for mix reconstruction and mortar matching.

Historic Mortar Analysis

Scanning Electron Microscopy (SEM)

This test can assist in the small-scale determination of the composition of individual particles in the original binder that cannot be detected in bulk analysis or by microscopy. Historical mortars can contain unusual ingredients which may or may not be important in the analysis.

Initial Rate of Absorption (set of 5)

This test can assist in the small-scale determination of the composition of individual particles in the original binder that cannot be detected in bulk analysis or by microscopy. Historical mortars can contain unusual ingredients which may or may not be important in the analysis.

Compressive Testing (Set of 5)

ASTM C-67: This test determines the average compressive strength of a clay brick masonry unit based on 5 samples.

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When should I use ASTM C1324 for mortar analysis?

Before specifying mortar testing it’s essential to carefully determine what information you want to obtain from mortar analysis and how you plan to apply it. Testing options vary widely as to cost, lead time, and resulting data so establishing the test goal is important to clarify early in the project. The most common reasons specifiers contact us for mortar testing are:

  • To identify the original for restoration.
  • To determine if a replacement mortar is contributing to building deterioration.
  • To provide documentation to support restoration plans for a historic preservation commission or other oversight group.

 

ASTM C1324 vs. ASTM C270: What are the differences?

ASTM C1324 is a test method used to identify the composition, characteristics and volumetric proportions of a hardened masonry mortar. 

ASTM C270 is the specification for masonry mortar to be used in masonry unit construction. It allows for four types of mortar (Types M, S, N, and O) to be produced using either the property or proportion method. 

 

What does an ASTM C1324 analysis report look like?

An ASTM C1324 report contains a narrative description of the petrographer’s findings describing the mortar, along with thin-section micrographs showing general characteristics and microscopic features, including mineralogy, shaped, and distribution of aggregate.  Images are magnified and taken using plane-polarized light and partially crossed polarized light. The report also includes the chemical analysis findings and supporting data. 

How accurate is ASTM C1324 in determining material proportions?

The chemistry portion is generally very accurate when combined with the thin-section or petrographic analysis. The petrographer’s analysis is used to adjust for any interferences, such as calcareous aggregates, which may skew the results. For this reason, chemistry should only be performed in conjunction with petrography. 

 

How do I test for compressive strength in ASTM C-1324?

There is no ASTM standard test to determine the compressive strength of an extracted sample. The standard test for compressive strength is ASTM C-109 “Standard Test Method for Compressive Strength of Hydraulic Cement Mortars” which involves compression testing a set of 2 inch cubes. Obviously, this procedure doesn’t translate to smaller, irregular samples pulled from a wall. Some testing facilities offer compressive strength testing for historic mortars but such proprietary tests rely on undisclosed methods, meaning that the results can’t be independently verified or analyzed and it’s impossible to determine how sound the methodology is.

However, we can use the ASTM C1324 results to judge the characteristics, composition, and proportions of the original mortar and with that information we can identify the most sympathetic replacement materials. 

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