Masonry Sand - When is it Too Fine?

A plethora of very fine (particle size) masonry sands are being used on the masonry portion of construction projects, especially throughout the Mid-Atlantic region of the United States. These fine masonry sands do not comply with the code according to ASTM C 144. ASTM C144, “Standard Specification for Aggregate for Masonry Mortar,” is the standard that governs whether a masonry sand gradation complies with the building code or not. When is the gradation of masonry sand too fine for masonry mortar production? Although not simple, the answer is straightforward but difficult to explain from a building code standpoint.

ASTM C144 is adopted by the masonry code (TMS 602), which means that ASTM C144 is code, and masonry sands must comply with ASTM C144 requirements. Please note the Section 4.4 narrative of ASTM C 144 in the image highlight box below. Although many natural masonry sands are finer in particle size than allowed by ASTM C144, Section 4.4 allows these noncompliant sands to be used to produce mortar if the resultant mortar from the noncompliant sands complies with Table 1 “Property Specification Requirements” of ASTM C 270. In other words, if the masonry contractor has a masonry mortar mix prepared by a laboratory (using a noncompliant masonry sand that is too fine) and if the resultant mortar properties comply with Table ASTM C270, Table 1, the contractor can use noncompliant sand on the project.

There are additional code compliance criteria other than ASTM C144 grading requirements, of course. Those requirements include maximum allowable criteria for deleterious materials, aggregate quality soundness test criteria, etc. All masonry sand project submittals or “certificates of compliance” should include a statement verifying compliance with ASTM C144. Suppose such a statement is missing from the submittal. In that case, the submittal should include a laboratory mortar mix design that verifies the mortar produced from the masonry sand (that is noncompliant with ASTMC144) complies with the requirements of Table 1 of ASTM C270. This is the process required by the verbiage of Section 4.4 of ASTM C144.

ASTM C144 Section 4.4 When an aggregate fails the gradation limits specified in 4.1 and 4.2, its use is permitted provided the mortar can be prepared to comply with the aggregate ratio, water retention, air content, and compressive strength requirements of the property specifications of ASTM C270, “Standard Specification for Mortar for Unit Masonry.”

For more information or further enthusiastic discourse on topics of CODE, please contact Alan Tuck at: [email protected] or 540.344.7939.