Under the auspices of ASTM Committee C-01, an inter-laboratory study (ILS) was conducted to determine precision and bias for bond-wrench testing carried out under the requirements of ASTM C 1329-98 (“Standard Specification for Mortar Cement”) and ASTM C 1357-98a (“Standard Test Methods for Evaluating Masonry Bond Strength”). The study involved 3 mortars, 15 laboratories and 17 sets of data. Using the statistical analysis procedures of ASTM E 691-99 (“Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method”) and the computer software developed to carry out those procedures, values of intra-laboratory repeatability, r, and inter-laboratory reproducibility, R, were developed. Normalized repeatability decreases from about 30% of the mean tensile bond strength with the least restricted data subsets, to about 20% of the mean tensile bond strength with the most restricted data subsets. Normalized reproducibility decreases from about 60% of the mean tensile bond strength with the least restricted data subsets, to about 40% of the mean tensile bond strength with the most restricted data subsets. Potential factors contributing to repeatability and reproducibility are discussed.