Modern Masonry Using Pre-blended Mortar

Blending and certification in the factory overcomes field mix uncertainties
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Sponsored by Echelon™ Masonry by Oldcastle
By Peter J. Arsenault, FAIA, NCARB, LEED AP
This test is no longer available for credit

Specifying Pre-Blended Mortar

In general, it should be clear by now that mortar is critical to a masonry wall’s structural integrity and aesthetic value. Therefore, specifications for it must be based on good information, and quality assurance tests must be applied correctly. Architects writing specifications for mortar need to be aware of the differences and specific capabilities of the different mortar types, making good spec writing critically important. Under the MasterFormat specification standard, masonry mortar is normally including in Section 04 05 13 or related sections.

Under Part 1: General of a standard three-part specification, the performance standards should be listed, including ASTM C270 and ASTM C1714, for the mortar and whether property specifications need to be followed or if proportion specifications will be acceptable. Also list the relevant standards for each ingredient and any relevant details related to them. This is a case where it makes sense to always request a complete submittal package so the materials, colors, and any admixtures can be fully inspected and confirmed. It also makes sense to request that a sample or test panel be constructed to see the product on the site before it is incorporated fully into the project. Be sure to call for it to be washed and cured for seven days on-site before being evaluated. As part of the quality assurance of the mortar, distinguish between on-site testing and material testing in a laboratory and request laboratory-certified test results. Verify that the same materials used in the test panel are the ones that were specified and tested.

Under Part 2: Products, there should be reference to a masonry schedule or other information on the drawings if multiple types of masonry construction and mortar are being used so the locations are clear. The specification should then go on to provide the details of each of the scheduled or identified products. If pre-blended mortar is being specified, then it should be clearly stated along with any restrictions against site-mixed mortar. Either way, identify each type of mortar needed (M, S, N, O) and where each is called for. If colored mortars are being used, then the specific colors need to be identified. Overall, specify consistent mortar materials, pigments, and mixing procedures.

In terms of Part 3: Installation Requirements, proper handling of all mortar materials on-site, whether pre-blended or otherwise, needs to be emphasized. If the mortar is pre-blended, then no instructions need to be given related to mixing other than the means of adding water. Final placing, protecting, and cleaning in a manner consistent with PCA and other approved standards or methodology will round out the specification.

The back side of CMU and mortar treated with an admixture to improve water repellency is shown on the left compared to CMU and mortar without the admixture on the right.

The back side of CMU and mortar treated with an admixture to improve water repellency is shown on the left compared to CMU and mortar without the admixture on the right. Both were sprayed with water on the front side, and after a short time, the difference in water repellency was clearly evident.


With an understanding of the importance of masonry mortar and the clear advantages of pre-blended mortar, the final question isn’t why would you use it on your projects, but rather, why wouldn’t you specify pre-blended mortar? The structural integrity of the mortar is easier to assure, and the aesthetic values are more controllable. Pre-blending provides better quality control and consistency with full technical support available from manufacturers. Further, it produces less waste and can improve job-site safety for workers.

Peter J. Arsenault, FAIA, NCARB, LEED AP, is a practicing architect, green building consultant, continuing education presenter, and prolific author engaged nationwide in advancing building performance through better design.

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Originally published in Architectural Record
Originally published in April 2017