Masonry grout is a flowable concrete material used in masonry cavities and cavity walls to stiffen the wall and strengthen the wall’s steel reinforcement system.  Grout may also add mass to a wall system for the purpose of thermal improvement or sound transmission reduction. Grout is made from cement, smaller coarse aggregates, fine aggregates (often sand), and water. Water content in grout is important as the balance between flowability and proper water/cement ratio must be considered. Also, water is absorbed into the masonry units once it is poured into the wall which must be accounted for in the mix.There are two types of masonry grout, fine and coarse.

Fine grout uses aggregates smaller than 3/8″, is often the same compressive strength of course grout, but flows better in tight spaces. Also fine aggregates are more difficult to segregate making them more popular when dropping from high distances.

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Aggregate Gradation for Fine Grout Mix

Course grout will include aggregates that are up to 1/2″ in diameter and will often be a less expensive mix due to the lower cost of larger aggregates.

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Masonry grout is typically mixed by hand, in a mortar mixer, or other powered mixer on site for small quantities. Similar to mortar, some projects may warrant a small site-built batch plant or silo which will release grout into the mixing unit, simplifying the dry mix process and increasing overall productivity.

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For large quantities, grout is produced at a concrete batch plant and delivered in a ready-mix concrete truck.

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As grout for masonry work is most commonly placed within the wall cavity or within CMU block voids, the chute on a ready mix truck often cannot reach the top of the masonry wall for grout placement. In this case, a concrete hopper or grout pump may be utilized. A concrete hopper is a metal hopper unit with a opening/closing hatch which can be lifted into place with a backhoe/excavator or forklift.

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Grout pump receiving material from Ready-Mix truck

A grout pump (or grout hog) is a hopper unit coupled with a gas-powered pump which discharges fine or course grout through a closing/opening hatch and through a hose into the masonry wall or cavity. A grout pump can also be lifted to higher elevations with a backhoe/excavator or forklift.

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