Why Grout CMU Cores?
**Grout filling** the cores of a Concrete Masonry Unit (CMU) wall is essential for structural integrity, particularly in load-bearing walls, tall walls, or in areas with high wind or seismic activity. The grout locks the reinforcing steel (rebar) into the blockwork, transforming the wall from a simple stack of blocks into a unified, reinforced concrete structure.
Grout Volume Calculation Principle
The volume of grout is calculated based on the area of the wall and a constant derived from the internal volume of the block cores. $$\text{Volume per Sq. Ft. of 8" Wall} \approx 0.014 \text{ ft}^3$$ $$\text{Volume (ft}^3) = \text{Wall Area (ft}^2) \times 0.014 \times \frac{\text{Fill Height (in)}}{8 \text{ (in)}}$$ $$\text{Volume (yd}^3) = \frac{\text{Volume (ft}^3)}{\text{27}}$$ The constant **0.014 ft$^3$/sq. ft.** is the standard consumption rate for fully filling the cores of a standard 8-inch CMU. This calculator scales that volume based on the required fill height.
Key Grouting Considerations
Grout Material and Mix
- **Fluidity:** Grout must be highly fluid (high slump) to flow around the rebar and fill all voids completely.
- **Aggregate Size:** Fine grout (small aggregate) is used for narrow cores; coarse grout (larger aggregate) for wider cores.
- **Lift Height:** Grout is typically poured in "lifts" of no more than 4-5 feet at a time to prevent blowouts and ensure proper consolidation.
Cleanouts and Inspection
- **Cleanouts:** The bottom block of each grouted cell must have a cleanout opening to remove debris before the final pour.
- **Reinforcement:** All grouted cores must contain **vertical rebar** (steel reinforcement) as specified by the engineer.
- **Consolidation:** The grout must be consolidated (vibrated) after pouring to eliminate air pockets and ensure a dense fill.
Engineer's Instruction is Paramount:
Never assume which cores need to be grouted. Your project's structural drawings will specify if cores should be **fully grouted** (all cores filled), **partially grouted** (specific cells filled, usually those with rebar), or left empty. Always follow the engineer's plan.