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Calculate grout, concrete, or foam insulation needed to fill concrete masonry units (CMU). Determine material quantities, rebar requirements, and project costs for your block wall construction.
0.00 cubic feet
80lb grout bags (0.5 cu ft yield each)
8" block: 0.5 cu ft per block
12" block: 0.8 cu ft per block
Bags: Volume ÷ 0.5 cu ft/bag
Cu Yards: Volume ÷ 27
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Filling concrete masonry units (CMU) with grout, concrete, or foam insulation serves several critical purposes in construction:
Building codes typically require filling blocks that contain rebar, bond beams, and structural cores. Retaining walls, foundation walls, and load-bearing walls often need full or partial grout fill for strength.
Grout typically costs $8-15 per 80lb bag. Full fill significantly increases material costs, so engineers often specify partial fill patterns (every other core) when possible.
| Feature | Grout | Concrete |
|---|---|---|
| Aggregate size | Fine aggregate, flows easily | Larger aggregate, may jam |
| Consistency | Flowable, pourable (7-11" slump) | Stiffer mix (3-5" slump) |
| Best for | Narrow cores, vertical pours, rebar | Large cavities, horizontal pours |
| Strength | 2500-3000 psi typical | 3000-4000+ psi |
| Cost | $8-15 per 80lb bag | $125-150 per cu yd (cheaper bulk) |
| Code compliance | Specified by most codes for CMU | May require approval |
Recommendation: Use grout for standard block wall construction. It's specifically designed for CMU work and meets building code requirements. Use concrete only for large cavities or when specified by an engineer.
| Block Size | Dimensions | Volume per Block | Bags per Block |
|---|---|---|---|
| 8×8×16 Standard | 8" × 8" × 16" | 0.5 cu ft (both cores) | 1 bag (80lb) |
| 12×8×16 | 12" × 8" × 16" | 0.8 cu ft | 1.6 bags |
| 6×8×16 | 6" × 8" × 16" | 0.3 cu ft | 0.6 bags |
| 10×8×16 | 10" × 8" × 16" | 0.65 cu ft | 1.3 bags |
Note: Volumes assume filling all cores completely. Actual usage may vary by ±10% depending on block manufacturer, mix consistency, and waste.
Filling block cores with foam insulation dramatically improves thermal performance while maintaining structural strength when combined with partial grout fill at required locations.
Unfilled 8" CMU wall: R-2 to R-3
Foam-filled 8" CMU wall: R-12 to R-15
This represents a 400-500% improvement in thermal resistance, significantly reducing heating and cooling costs.
Structural cores must still be filled with grout where rebar is present. Foam insulation is used in non-structural cores only. Always follow structural engineer's specifications.
Vertical rebar should be placed before block laying begins. Horizontal bond beam rebar is placed in special U-block or knockout blocks. Ensure minimum 3/4" cover on all sides.
For a typical 8" block wall with full grout fill, expect $8-15 per block in material costs (grout only). A 100-block wall would cost $800-1,500 in grout. Labor adds $3-6 per block, so total installed cost is typically $11-21 per block.
No. Only structural cores, bond beams, and cores containing rebar require filling. Non-load-bearing partition walls and above-grade walls in low-wind areas may not require fill. Always follow building codes and structural plans.
Fine grout uses sand aggregates up to 3/8" and is required for grout spaces less than 2" wide. Coarse grout can use up to 1/2" aggregate and is for spaces 2" or wider. Most block cores require fine grout due to narrow spacing.
Grout reaches handling strength in 24-48 hours and design strength in 28 days. Don't apply loads to grouted walls for at least 3 days. In cold weather (<40°F), protect grout and allow extra cure time.
It's not recommended. Regular concrete has larger aggregate that can jam in narrow cores and may not flow properly around rebar. Grout is specifically designed for masonry work with finer aggregates and higher slump. Some jurisdictions prohibit using concrete in CMU.
For 8×8×16 blocks: Multiply wall length (ft) by height (ft), then multiply by 1.125 blocks per square foot. Example: 20' × 8' = 160 sq ft × 1.125 = 180 blocks. Add 5-10% for waste and cuts.
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