How to Install Cinder Block

Dig out and level the area along which your wall will be constructed. If you need to dig a trench, it should be at least a foot deep. Cinder block walls absolutely must be built along completely flat, even surfaces. Smooth the wall's footprint area until it is level and flat. Use an actual long level to make sure that its whole length is on an even grade. For even better accuracy, you can use a string line attached to two posts at either end of the wall site. Verify that the string line is not at an angle with the level, and flatten your wall site so that it is in line with the string.

Build a plywood form that is at least 5 inches wider and a 6 inches longer on each side and each end respectively than your block wall. The form should also be at least 8 inches deep. Fill this form to about three-quarters of its depth with ready-mix concrete that you have mixed with water in a wheelbarrow. You want the concrete to have the consistency of pudding. Make sure the concrete fills the form completely and tamp it flat and level. Allow it to harden.

Lay down your first line of cinder blocks, each flush against the next. Use the string line you have already attached for leveling to make sure they are in a straight line. Pour another 2 to 4 inches of concrete around the bottoms of the blocks and allow it to harden. This will top up the form and give your wall extra strength as the bottom blocks are now fused into the concrete footing. If the blocks at either end of the wall are too long, you can split them in half using a mallet and chisel, aligning the smooth end so that it makes up the edge of the wall.

Drill holes into the concrete footing on the inside of every second hole in the bottom layer of blocks. You'll want to drill a hole that's about 5 to 6 inches deep and 3/4 inch wide. Hammer lengths of 1/2-inch to 3/4-inch rebar into these holes and, if necessary, use concrete adhesive to glue them in place. These lengths of rebar should all reach up at least to two-thirds of your wall's height and all be the same length. Ensure that they stay relatively upright.

Mix a batch of mortar and trowel it onto the top of the first layer of cinder blocks. Having done this, work quickly to lay down the next layer of blocks. Make sure you lay the next layer in such a way that the joints between blocks don't line up with the joints of the blocks in the layer below. This applies for all the layers of blocks you place on the wall.

Add subsequent levels of blocks with the same process as you did with the second level, laying mortar under each new level. Move the rebar around a bit if needed so that it does not get in the way of your work. At this point you should also strip away the plywood that held your form together.

Once you have topped the wall to its desired height, you'll need to fill the deep holes inside it with either fine crushed gravel, pea gravel, sand or concrete. If you want the wall to be truly strong, highly liquid concrete is your best bet, but the other fillers will also create a very strong wall, especially with the rebar inside the holes reinforcing it. Use a long 4-by-4 beam to tamp the filler material periodically as you fill the holes. This will make sure it packs into its space solidly. Fill the holes inside the wall to the top.