Masonry Magazine July 1974 Page. 22
vibrated in place with a 1 in. by 2 in. wood pole or a flexible cable vibrator. The principal advantage of "low-lift" grouting is that cleanout or inspection openings are not required since adequate inspection can be made from the top of the construction.
In high-lift grouting, the grouting operation is delayed until the masonry wall is laid up to story height. This grouting method offers several advantages. A larger volume of grout can be placed at one time, thereby permitting the economical use of more expensive equipment, such as the grout pump; vertical steel can be easily picked without splices and the location of steel can be readily checked by the inspector prior to grouting. Proper preparation of the grout spaces before grouting is very important. All mortar droppings and other foreign debris should be removed through the cleanout openings which should be not less than about 3 by 4 in. Cleanout openings should be made in the face shells of units before the units are placed in the first course at the bottom of the wall. A specially scored unit is used occasionally to permit easy removal of part of the face shell. When both sides of a block are to be exposed to view, it may be necessary to omit the entire face shell to provide the necessary cleanout opening (Figure 2).
After the grout spaces are checked for cleanliness and reinforcement positioned, the cleanouts are then closed by inserting face shells of masonry units, mortaring in units that were left out, or by forming over the openings
to allow grouting to the plane of the wall. Face shell plugs or mortared units should then be adequately braced to resist the pressure of fluid grout. In hollow unit masonry, the mortar should be permitted to cure 24 hours before grouting. When filling the cavity space between two wythes of masonry, a period of not less than 3 days is recommended to allow the mortar to gain the necessary strength.
In high-lift grouting, the grout is generally placed in 4 ft. lifts and is puddled or vibrated immediately following placement (Figure 3). After waiting about 15 to 60 minutes to allow for grout settlement and absorption of excess water into the masonry, the next 4 ft. grout lift can be placed. The waiting period depends on weather conditions and absorption rates of the masonry. If the timing is suitable, reconsolidation of the previous pour and consolidation of the succeeding pour may be done in the same operation. The full height of any section of the wall should be completed in one day.
As soon as possible after the grouting is completed, all exposed block faces which may have been streaked or spotted with grout should be washed down thoroughly with water. Ungrouted walls should be adequately braced to prevent damage by wind or other forces.
NATIONAL CONCRETE MASONRY ASSOCIATION
P.O. Box 9185, Rosslyn Station, Arlington, Virginia 22209