Masonry Magazine February 1989 Page. 26
Low-Lift Grouting
Masonry should be placed above the bond beam to permit grouting the bond beam in one operation. The grout pour should then stop approximately ½ inch above the bond beam course.
Place vertical reinforcement where required, insuring that cavities containing reinforcement have a continuous unobstructed cross sectional area of at least 8 square inches with a minimum dimension of 2 inches. (Uniform Building Code requires a 2 inch by 3 inch clear opening.)
Place grout of fluid consistency in those cavities which contain properly positioned reinforcing bars and all other cavities required to be grouted.
Consolidate the grout with a vibrator or puddling stick.
Repeat the operation at the next higher level.
Low-lift grouting requires no special concrete block shapes or special equipment. The vertical steel reinforcing bars are relatively short in length, and may be spliced by overlapping a distance of 30 bar diameters for Grade 40 bars and 36 bar diameters for Grade 60 bars. This overlap insures sufficient transfer of stress at the splice. Two methods of grout placement are acceptable, hand bucketing or pumping, whichever is most advantageous to the contractor. Complete consolidation of the grout is required by puddling with a 1"x2" wood pole or vibrating with a flexible cable vibrator. The grout lift should not terminate at a mortar bed joint nor where horizontal reinforcing bars are placed. A groût key between lifts at least ½" below the mortar joint insures adequate shear transfer. One layer or course may be laid above the lift height to obtain proper grout coverage of horizontal reinforcing and the grout is poured to a height approximately ½" above the bed joint. The final lift is poured to the top of the wall. Typical reinforced hollow unit concrete masonry construction using low-lift grouting is shown in Figure 1:
High-Lift Grouting
On larger projects, grouting may be delayed until the wall has been laid up story height or to the full height of the wall. Grout is then placed into the wall in several succeeding 4 foot maximum lifts. This procedure is termed "high-lift" grouting and requires the use of a grout pump (Figure 2). The advantages of high-lift grouting on larger projects are obvious. Placement of the vertical steel can be done after the wall is erected; its location can be checked by the inspector; and the grout can be transit-mixed and placed by grout pump within a relatively short time.
Cleanout holes of sufficient size for the removal of mortar droppings and other debris should be provided at the bottom of all vertical cavities containing reinforcement. The grout space must be clean prior to grouting.
FIGURE 1-TYPICAL REINFORCED CONCRETE MASONRY CONSTRUCTION USING THE LOW-LIFT GROUTING TECHNIQUE
Place metal lath under bond beam to confine grout.
Steel in bond beams is set in place as wall is laid up. Lap minimum of 30 bar diameters (grade 40), 36 bar diameters (grade 60) at splices.
Vertical steel-Lap minimum of 30 bar diameters at splices (36 for grade 60): hold in position top and bottom and at intervals of 192 diameters.
Stop grout lift from top.
Consolidate each lift with vibrator or puddling stick.
Floor Slab
Footing.
Unless wall is fully ground, place mortar on cross webs adjacent to cells which will be grouted to prevent leakage.
Cells containing steel are filled solidly with grout, vertical cells should provide a continuous cavity, free of mortar droppings, and at least 2x3 Inches in size.
FIGURE 2-High-lift grouting using a grout pump.
FIGURE 3-OPEN-END CONCRETE BLOCK
"H" Shaped Mortarless Head Joint Unit
"A" Shaped Unit