Concrete Block Wall
CMU count and mortar bags for a wall — standard 8×16 block.
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The engineering
Assumptions, stated plainly: a nominal 8×16-in CMU laid with 3/8-in mortar joints covers exactly 8/9 ft² of wall, giving the classic 112.5 blocks per 100 ft² — the 1.125 factor here. Mortar is figured at one 80-lb bag of premixed Type N/S per ~28 blocks, a common manufacturer yield; actual usage swings with joint tooling, waste, and whether cores get grouted (grout is NOT included here).
The block count is rounded up but carries no breakage allowance — masons typically add 5%. Subtract door and window openings with the third field; for anything structural, cell grouting, vertical rebar spacing, and bond-beam courses come from the engineered drawings, not from this card.
Where this math comes from
The hollow concrete block is a 1900 invention: Harmon S. Palmer patented a cast-iron machine that molded blocks one at a time, and within a decade thousands of backyard block plants were running — Sears, Roebuck sold the machines by mail order. The Besser company's automated machinery in the following decades turned the block into the cheapest wall in America.
Standardization did the rest: ASTM C90, first issued in 1931, fixed the dimensions and strengths so that a block from any plant lays up the same wall — which is why one multiplier can estimate every CMU wall in the country.
- 1900Harmon S. PalmerPatents the hollow-block molding machine — the CMU is born.
- 1904Herman BesserBlock-making machinery industrializes; blocks become a commodity.
- 1931ASTMC90 standardizes load-bearing CMU dimensions and strength.
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