Block Wall Takeoff
CMU count with openings and breakage, mortar bags from joint volume, vertical and horizontal rebar, grout for solid-grouted walls, lintels, and weep holes.
A nominal 8x8x16 face block covers 1.125 per sq ft with a 3/8 in joint, and breakage on a cut wall runs 5%. Grouted solid takes about 1 bag of grout per 10 sq ft of wall.
How the math works
- Blocks: wall sq ft × 1.125 blocks per sq ft (a nominal 8x8x16 with a 3/8 in joint nets 137 sq in of face), minus openings, plus 5% breakage. 1,320 sq ft of wall = 1,485 blocks.
- Mortar: joint volume per block = 9.1 sq in × 3.75 in depth = 0.0198 cu ft; an 80 lb bag yields about 0.63 cu ft, which is the source of the 1 bag per 30 blocks rule of thumb.
- Rebar: vertical bars at the design spacing, each cut to wall height plus a 4 ft lap; two continuous #4 bars run in the horizontal joints at 16 in o.c. (2 × wall length). #4 = 0.668 lb per ft, #3 = 0.376.
- Grout: solid-grouted wall takes about 1 bag of 50 lb grout per 10 sq ft of wall, grouted cells at 16 in o.c. about 1 bag per 22 sq ft. Grout after the rebar is set and the wall is clean, and above the highest weep.
- Lintel & weeps: lintel length = span + 8 in bearing each end (a 10 ft lintel per opening is the standard cut), weeps at 24 in o.c. in the highest course above the finished grade, cavity filled with clean stone to within 24 in of the top in drainage cavities.
How many blocks for a 40x8 wall?
320 sq ft of wall, 360 blocks with breakage at 1.125 per sq ft. Subtract the openings, then order 5% more than the arithmetic: block breakage on a cut wall is real and unopened bundles are returnable.
How many bags of mortar per 100 blocks?
About 3.3 bags of 80 lb per 100 face blocks, computed from joint volume (0.0198 cu ft per block against a 0.63 cu ft yield). Grout is separate: 1 bag of 50 lb per 10 sq ft of solid-grouted wall.
How many weep holes in a block wall?
One every 24 in of wall length in the highest course above the finished grade, over the cavity, with the weep clear of mortar squeeze-out. A 40 ft wall takes 20 weeps and 40 ft of cavity drainage stone.