Masonry Materials, Units, Mortar, and Grout Sampling
Units, mortar, and grout
Masonry field testing begins with knowing what is being sampled. Clay brick is specified under ASTM C216, concrete brick under C55, and concrete masonry units under C90; C140 provides the sampling and test procedures for concrete masonry units. Mortar is specified by ASTM C270 by type (M, S, N, O, and K), while grout for masonry is specified by ASTM C476. A candidate must distinguish preconstruction evaluation from construction evaluation and must know which standard governs each material: C780 for mortar, C1019 for grout, and C140 for concrete masonry units.
Sampling is a chain-of-custody operation. Obtain a representative sample, but do not substitute convenience for randomness: record the lot or batch, location, mixer, time, and weather. Mortar should be sampled before it stiffens, from several points in the batch or at the point of use, placed in a clean, nonabsorbent container, and remixed gently before testing. Grout is sampled similarly and molded promptly. Never retemper a sample to make it workable; that changes the water content and invalidates strength results.
Trap: questions often imply that one grab sample represents an entire day's production, or that a sample may be taken after the mortar has begun to set. Another trap is confusing unit standards (C90, C216) with test standards (C140). Rule of thumb: if the sample cannot be tested within the standard's time limit, discard it and take a fresh one; do not "fix" it with water.