Aggregate sizes for masonry grouts do not typically match the acceptable gradations for concrete. Aggregates for concrete are typically coarser and harsher compared to aggregates for masonry grout. Most aggregate suppliers will therefore carry ‘mortar sand’ or ‘masonry sand’ to allow for the batching of CSA-compliant masonry grouts. Additionally, the aggregate gradations are also different between fine and course grouts. Gradation requirements for aggregates in masonry grouts are found in Table 1 of CSA A179-14 Mortar and grout for unit masonry.

Both grout types are suitable for masonry construction, but each has its own advantages. A coarse grout will require less cement per volume, and it is generally a less expensive alternative to fine grout, while fine grout is required in heavily reinforced or otherwise congested masonry. For instance, when both vertical and horizontal reinforcement are present, especially at lap splice locations, a fine grout can better facilitate a complete bond between the grout, reinforcement, and masonry units, while reducing the probability of voids.

Depending on the unit size and reinforcement configuration, fine grout may be required to satisfy minimum reinforcement clearances within the masonry unit cell, as covered within CSA A371-14 Masonry construction:

This is one case where the CSA standards call for one particular grout type. So long as a grout meets all other provisions within CSA A179 through either compliance pathway, the masonry contractor can opt to use either fine or coarse and expect satisfactory results.

There are no minimum strength requirements for proportion specified grouts, because they have a proven record of performance through past experience and decades of research.

Masonry assemblage design strengths found in CSA S304-14, Table 4 are based on proportion specified grouts. Proportion specified grouts will typically test to a minimum compressive strength of 10 to 12 MPa at 28 days when cast in non-absorbent cylinder molds. However, once again, there is no minimum strength required if the grout is mixed to the correct proportion specification.

The minimum 28-day compressive strengths for property specified grouts are 10 MPa and 12.5 MPa, for fine and coarse grout, respectively. Designers familiar with concrete construction, or with grout products in general, may think that this strength is low. However, the compressive strength of grout used in masonry construction is affected by its consistency at the time of pouring, by the size of the voids it will need to fill, and by the level of absorption of the masonry units in contact with the grout.

The following key properties differentiate masonry grouts from traditional concrete:

Masonry grouts meeting the proportion specification of CSA A179, using conventional materials and procedures, have a proven record of performance. They have the properties required for grout in new masonry construction.

However, some have believed that non-shrink or expansive grout can improve the properties of masonry construction and as a result, certain manufacturers have therefore taken to producing pre-blended property specified grouts with expansive agents to decrease shrinkage. Although it is possible for grouts which comply with the performance specification requirements of CSA A179-14 to contain an expansive agent, the manufacturer of such a product must still demonstrate that it meets all requirements of the standard. No benefit to the masonry assemblage, from the use of non-shrink or expansive grout, should be assumed without verification through assemblage testing, provided by the manufacturer, and approved to the satisfaction of the designer. Designers are reminded, that the testing performed for the determination of the strength and durability properties of masonry assemblages as part of the development of CSA standards has been conducted using a conventional proportion-specified grout (without any additives, plasticizers, or expansive agents).

While each manufacture’s product will differ, caution is required when specifying a proprietary non-shink grout mix and it is critical that the specified mix be intended for use in masonry construction. Certain types of non-shrink grouts, not intended for masonry, are mixed to a very low or no slump, have very low water-to-cement ratios, and do not meet the requirements of CSA A179. Non-shrink grout products are often used for highly localized applications, such as under bearing surfaces such as base plates. Any proprietary product intended for a specialized application, and for which each manufacturer provides guidelines through their own specification, should be understood by the designer and the contractor prior to its use.