To work out the correct ratio for mixing quantities of mortar — where it relates to how many cinder blocks one bag of mortar mix will lay — it’s important to realize that the quantities will change significantly depending on the size of brick used. A simple standard, however, would be as follows: 2.5 bags of pure mortar mix and 600 pounds of sand per each 100 blocks you intend to lay. This ratio is based on a standard 8 x 8 x 16 inch concrete block.

These quantities would change significantly for brick, however, since the average brick is so much smaller than a concrete block. You would need many more bricks than blocks in a construction such as a wall. This, of course, would mean a lot more bed joints and more vertical head joints than with larger size bricks or concrete blocks. For standard brick though you need approximately 7 bags of pure mortar mix and 3,000 pounds of sand per one thousand bricks. Therefore a wall consisting of 1,500 bricks would require about 10.5 bags of mortar and 4,500 pounds of sand.

It’s also important to realize that brick and cinder block are set using differing mortar mixes, so it’s important to purchase all mortar and sand for the job at the same time so as to keep mortar color consistent. If you mix different batches of sand and mortar then there will be a good chance that you will end up, unfortunately, with different color mortar once dry.