How much mortar do you need?

How much mortar do I need?

It depends on what you are laying. For modular brick with ⅜ inch joints, the Brick Industry Association gives 5.5 cubic feet of mortar per 100 square feet of wall; with 25% extra and 80 lb bags that each yield about 0.54 cubic feet, 100 square feet takes 13 bags. For 8 × 8 × 16 inch concrete block, Quikrete's figure of 13 blocks per 80 lb bag means about 9 bags for 100 square feet.

How many bricks does a bag of mortar lay?

Quikrete says an 80 lb bag of Mortar Mix lays up to 37 standard bricks, or 13 standard concrete blocks. Modular brick uses less mortar per brick than standard, and ½ inch joints use about a quarter more than ⅜ inch joints.

Which mortar type should I use?

Type N is the general-purpose mortar for above-grade walls, chimneys and veneer. Type S is stronger, for below-grade work, retaining walls and patios. Pre-mixed bags such as Mortar Mix are Type N unless the bag says otherwise.

Why add extra mortar?

Mortar drops off the trowel, gets left in the mixer and stiffens before it is used. The Brick Industry Association recommends adding 15 to 25% for waste; the calculator uses 25% for brick.

Can I mix my own mortar instead?

Yes — Type N mortar is roughly 1 part masonry cement to 3 parts sand. Bagged mix costs more but is consistent from batch to batch, which keeps the color of the joints even. Compare the prices of the bag sizes in the table.

What is the difference between mortar and grout?

Mortar bonds the units and fills the bed and head joints between bricks or blocks. Grout is a thinner, wetter mix poured into the hollow cores of concrete block (usually where reinforcing bar sits) or into wide spaces. This calculator counts mortar for the joints only; for filled cores use the grout calculator.

How much does a bag of mortar yield in cubic feet?

The calculator uses 0.54 cubic feet per 80 lb bag, taken from the manufacturer's statement that a bag lays up to 37 standard bricks and from the Brick Industry Association's mortar quantity of 14.5 cubic feet per 1,000 standard bricks (37 × 14.5 ÷ 1,000). The 60 and 40 lb bags are counted in proportion to their weight.

Does the type of brick change the amount?

Yes. A bigger brick has fewer joints per square foot of wall. In the Brick Industry Association figures used here, a 100 square foot wall of modular brick with ⅜ inch joints takes 5.5 cubic feet of mortar, utility brick 3.7 and standard brick 9.5, before the 25% allowance for waste.

How the calculation works

For brick, the calculator multiplies the wall area by the mortar volume per square foot for the chosen brick and joint (Brick Industry Association, Technical Note 10), adds 25% for waste, and divides by the volume of a bag. For concrete block it uses the manufacturer's coverage of 13 blocks of 8 × 8 × 16 inches per 80 lb bag and about 1.125 blocks per square foot of wall face. Doors and windows are subtracted from the wall area first, and the bag count is rounded up to whole bags.

Worked example: a brick wall with a door and a window

A wall 20 ft long and 8 ft high has 160 square feet. A door (21 square feet) and a window (15 square feet) come off, leaving 124 square feet. In modular brick with ⅜ inch joints that is about 837 bricks at 6.75 per square foot, and 8.5 cubic feet of mortar including the 25% allowance (124 × 5.5 ÷ 100 × 1.25). One 80 lb bag covers 7.8 square feet of this wall, so 124 ÷ 7.8 = 15.9 rounds up to 16 bags.

With ½ inch joints one bag covers 6.2 square feet and the same wall needs 20 bags. If the wall were 8 × 8 × 16 inch concrete block instead, one bag covers 11.6 square feet and the wall needs 11 bags.

Common mistakes

Estimating from the number of bricks per bag alone ignores joint width, and the wider the joint the more mortar the same wall takes. Forgetting that the 25% allowance is already included for brick, then adding another 25% on top, piles one margin on another; the Extra on top note explains when a small additional allowance makes sense. Block cores filled with grout are not part of this count. Finally, bags of different weights hold different amounts, so compare the price per bag size by the cost per square foot of wall, not per bag.

Sources: Brick Industry Association, Technical Note 10 (mortar quantities per 100 square feet); Quikrete Mortar Mix coverage (37 bricks or 13 blocks per 80 lb bag). Related: brick calculator, concrete block calculator, grout calculator, stone wall calculator.