my Old Workshop

Concrete block walls 2 – ordering mortar

Last time, we calculated the number of blocks you need. Next step: calculate and mix the mortar for your wall.

To mix your own, each block requires about .003 cubic yards of sand and each cubic yard of sand requires 1/3 of a yard (12 bags) of masonry cement. The mix is one part cement, 3 parts sand, and as much water as you can add and still get a workable mix. The blocks will absorb the excess water.

Or, each block requires .162 bag of mortar mix.

The amount required to parge a wall (cover it with mortar) is about equal to the amount required to lay, so if you are laying and parging, double the amount you’ve calculated above.)

In our example last time, we calculated 378 blocks for our wall.

So, we need .003 X 378 = 1.1 cu. yd sand. We also need 12 X 1.1 = 13 bags of masonry.

Assume we are parging most of the way up and at least

half the wall will be below grade. Order a total of 2 cu. yds. sand, 10 bags type S masonry, and 10 bags type N masonry.

Or we could use .162 X 378 X 2 = 122 bags mortar mix.

Some tips:

1) If hand-mixing, save some work. Make a really sloppy mix with all the cement but short on sand, and only mix it a little bit. Leave it for 10 minutes. When you come back, the water will have soaked into the mix, and you can finish mixing it, adding sand to bring it to the right consistency.

2) If using the mortar for pointing (shaping the joint to prevent water damage), temper it by thoroughly mixing it, then letting it sit for half-an-hour, then re-mixing it. This reduces the chance of it shrinking in the joint.

Next, we’ll build it.