Count the wall, then order for it. Mortar is split by the product you actually buy, because masonry cement and premixed mortar are off by a factor of three.
Height rounds up to whole courses at 8″ each — a wall is only ever a whole number of courses tall.
Doors and windows, in inches. Deducted by area — order the lintels separately.
Vertical bars follow the grouted cells. Lap splices figured at 48 bar diameters.
Every masonry supply estimating guide prints the same figure: three bags of mortar per hundred block. That number is correct, and it will also put you three times short if you buy the wrong bag.
The guides mean a 70 lb bag of masonry cement, which you mix on site with roughly two and a half parts sand — about sixteen shovels a bag. One ton of mortar sand covers about seven bags, or about 250 block.
Premixed mortar such as Type S mason mix already has the sand in it. An 80 lb bag lays somewhere around twelve block, so a hundred block takes eight bags rather than three, and no sand at all. Same wall, same joints, completely different order.
Yields drift by brand, and a fat joint eats mortar fast — going from a ⅜″ joint to ½″ adds roughly half again. Check the bag and adjust the yield above.
An 8×8×16 block laid with ⅜″ joints occupies an 8″ by 16″ module, which is 0.889 sq ft, so a wall takes 1.125 blocks per square foot. That holds for every width in the table below — a 12″ block covers the same wall face as an 8″ one.
Running bond needs a half block at alternate course ends. That is one half block per two courses per end, and most yards will sell them cut.
| Block | Void each | Blocks per yard |
|---|---|---|
| 4″ | 0.10 ft³ | 270 |
| 6″ | 0.17 ft³ | 159 |
| 8″ | 0.24 ft³ | 112 |
| 10″ | 0.31 ft³ | 87 |
| 12″ | 0.38 ft³ | 71 |
Solid grouting is rarely what a drawing calls for. Partial grouting fills only the cells that carry steel, typically at 32″ or 48″ on center, which is a third to a quarter of the concrete. Follow the engineer's cell spacing rather than the default here.
Grout is not concrete. It is a high-slump mix, usually 8″ to 11″, designed to flow into a cell without segregating. Ordering structural concrete and adding water on site defeats the mix design.
1.125 with standard ⅜″ joints.
Only with masonry cement. Premix has it. About a ton per seven bags, or a ton per 250 block.
Four to five courses before the mortar in the bottom joints starts squeezing under the weight. Blowouts on grouted walls are a lift-height problem, not a mortar problem — grout in lifts and let it set.