How Many Bags of Mortar per 100 Blocks? Rule of Thumb

How many bags of mortar per 100 blocks depends on which product you buy. Standard 8x8x16 inch concrete blocks laid with 3/8 inch joints use roughly 8 to 8.5 cubic feet of mortar per 100 blocks. An 80-pound bag of pre-blended mortar mix makes only about 0.6 to 0.7 cubic feet, so you need about 8 bags per 100 blocks. A 70-pound bag of masonry cement mixed with about 3 cubic feet of sand makes far more mortar, so about 3 bags plus a third of a cubic yard of sand covers 100 blocks. Add 10 to 15 percent for droppings.

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Mortar per 100 blocks

Product	Per 100 blocks (8x8x16, 3/8 in joints)	With ~15% waste
80-lb pre-blended mortar mix	about 8 bags	about 9 to 10 bags
60-lb pre-blended mortar mix	about 10 to 11 bags	about 12 bags
70-lb masonry cement	about 3 bags	about 3.5 bags
Sand for masonry cement	about 9 cu ft (1/3 cu yd)	about 10 to 11 cu ft

These assume face-shell bedding, where mortar goes on the outer shells and the end webs. Full bedding under every web, common on the first course and in some structural walls, uses more.

Why the bag counts are so different

Pre-blended mortar mix already contains the sand, so most of the 80 pounds you carry is sand. Masonry cement is just the binder; you add about three times its volume in sand at the site. For a garden wall of 50 blocks, premix is convenient. For a foundation of 500 blocks, masonry cement and a sand delivery cost far less and save a lot of bag handling.

For brick

Brick walls have many more joints per square foot. Rough planning numbers for standard modular brick with 3/8 inch joints:

Pre-blended 80-lb mortar mix: about 1 bag per 35 to 40 bricks, or roughly 25 to 28 bags per 1,000 bricks.
Masonry cement: about 7 to 8 bags per 1,000 bricks, plus roughly 0.8 to 1 cubic yard of sand.

Check the bag label, since yields vary by brand and joint width.

Example: a 40-foot block wall, 4 feet tall

A wall 40 feet long and 4 feet high has 160 square feet of face. Standard blocks cover 0.89 square feet each, so about 1.125 blocks per square foot, or 180 blocks. Mortar: about 15 bags of 80-pound premix, or about 6 bags of masonry cement with roughly 0.6 cubic yards of sand, before waste. Grout for any filled cores is a separate order; see filling concrete block cores.

Mixing and working time

Mix only what you can use in about 90 minutes to 2 hours. In hot or windy weather, mix smaller batches and keep the board damp. Retemper once with a little water if mortar stiffens from evaporation, and throw it away once it starts to set. Our mortar mix ratio page explains Types N, S, and M.

Bottom line

Plan on about 8 bags of 80-pound premixed mortar per 100 standard blocks, or about 3 bags of masonry cement plus a third of a yard of sand. Add 10 to 15 percent for waste, use more for full bedding, and choose masonry cement with bulk sand for larger walls.

Questions people ask

How many bags of mortar do I need for 100 cinder blocks?

About 8 bags of 80-pound premixed mortar, or about 3 bags of masonry cement with roughly 9 cubic feet of sand.

How many blocks does one bag of mortar lay?

An 80-pound bag of premixed mortar lays about 12 to 13 standard blocks; a bag of masonry cement with sand lays about 30 to 35.

How much sand do I mix with masonry cement?

About 3 parts sand to 1 part masonry cement by volume, roughly 3 cubic feet of sand per 70-pound bag.

How many bags of mortar per 1,000 bricks?

About 7 to 8 bags of masonry cement plus sand, or roughly 25 to 28 bags of 80-pound premix.

Does mortar quantity change with joint size?

Yes. Wider joints use noticeably more mortar, so check the bag yield for your joint width.

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