Grout Lift Height in a 14-ft Fully Grouted Wall
A masonry subcontractor is building a 14-ft-tall, 8-in. nominal CMU wall for a single-story gymnasium. All cells are grouted, with No. 5 vertical bars at 24 in. on center and a bond beam at the 8-ft elevation. The wall has been laid for nine days. The subcontractor proposes to place the entire 14 ft in one continuous grout pour from the top, using a 4,000-psi coarse grout with a measured slump of 10 in., consolidating by lowering a 1-in. poker through the grout at 4-ft intervals along the wall. No cleanouts are planned. The special inspector also observes that mortar fins project about 3/4 in. into several cells at the bond beam and that the grout space at one corner is partly blocked by a mortar dropping. The contractor argues that the wall has been up nine days, so the mortar is strong enough to take the pressure of a single pour.
1. Can the one-pour grouting plan be approved? Explain the controlling limit and how the wall should be sequenced.
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No. The controlling provision is the grout-lift limit in TMS 602, not the age of the masonry. A grout lift is limited to 5 ft 4 in., so a 14-ft wall requires three lifts, for example 5 ft 4 in., 5 ft 4 in., and 3 ft 4 in., with each lift consolidated before initial set and the next lift placed while the previous lift is still green enough to bond. A single 14-ft pour is a high-lift operation: it requires an approved procedure, cleanouts at the base of the pour so the grout space can be inspected and cleared, and normally a self-consolidating grout verified by slump flow rather than a conventional slump. The nine-day mortar age only means the mortar has gained strength. It does not make the cells clean, does not let a vibrator reach the bottom of a 14-ft lift, and does not eliminate the pressure that can blow out face shells. The likely result of the proposed pour is voids, honeycomb, and unconsolidated grout at the base and under the bond beam. Require a lift-by-lift grouting plan and inspection before any grout is placed.
2. Evaluate the 10-in. slump and the proposed consolidation method.
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The 10-in. slump is within the 8-to-11-in. range that ASTM C476 permits for coarse grout, measured by ASTM C143, so slump alone is not a reason to reject the mix. But slump is only a consistency check; it does not make a 14-ft lift placeable. The proposed consolidation is the problem. Lowering a 1-in. poker at 4-ft intervals from the top of a 14-ft pour cannot reliably reach the lower part of the lift, and the vibrator must penetrate the full depth of the lift and slightly into the lift below to knit the grout. With proper 5-ft-4-in. lifts, a vibrator can be worked along the wall at close spacing; puddling is appropriate only for fine grout. The inspector should also verify that the grout is reconsolidated before initial set and that the contractor does not add water at the pump to restore slump.
3. What should be done about the 3/4-in. mortar fins and the partly blocked cell before grouting?
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Remove them. TMS 602 limits mortar projections into the grout space to 1/2 in.; a 3/4-in. fin is an obstruction that can block grout flow, create a void, and reduce bond and cover around the vertical bar. The partly blocked corner cell is more serious because grout cannot fill around the bar, leaving the reinforcement unbonded. Before grouting, the cells should be opened, the fins chipped off, and the grout space and bar position verified. The inspector should document the condition and require the contractor to change the troweling practice, striking mortar flat and keeping mortar out of the cells, before the next lift. If the blockage cannot be cleared through the top, a cleanout is needed.