Concrete Block: Tips and Tricks

Concrete block. It has been a building staple for many years. But how do you do it yourself? In this article, I will explain the in’s and out’s and do’s and don’ts of concrete block masonry. Concrete blocks come in many styles and shapes. Basic blocks are 8 inches tall and 16 inches long with two hollow cells in the middle. The empty cells create an insulating factor for heat as well as sound. Some other block designs are half highs, (4 inches high and 16 wide) singles, (8×8 inches) and my personal favorite, broken exterior (same size as a regular block, the exception is the exterior block face is broken and is used as the finished product. Think of wal-mart.)

Block is secured together with Portland cement and cells can be filled with steel and concrete for added strength. Usually corners, windows and door openings are filled with solid concrete cells. Depending on the local building code, cells are also filled every four to six feet apart. The entire top of the wall is tied together with steel and tied into the upright cells. It is then filled with concrete. This is called the “lintel”. While concrete block is strong enough on its own for basic walls, anything bearing weight derives its strength from the solid concrete cells and steel.

Start laying block on a foundation. This may be a concrete slab or footer. Do not set concrete block on the ground, it will sink or rise and it will destroy your wall eventually.When beginning a block wall, you will start on a corner first. Build the block wall up a few courses high and move to the next corner and repeat the process. After two corners or ends of the block wall have been established, use a string line and stretch it between the two corners. You can purchase a special tool for this process. It is called a line dog or string dog. It allows the string to be pulled tight between the blocks and hooks onto the edge of the block so it can stay while you work. The string verifies that your block is straight in, out, and up and down. Use mortar to make the block even up and down.

Work your way up to the top of the corner with the middle block. Once you have made the middle as high as the corners, you can begin to build the corners up to their proper height. Continue along filling in the center to finish the block wall.

At this point, you will need a sponge the smooth off the wet concrete that may be sticking out or fill in any voids where there is no mortar mix. If you plan to finish the wall with stucco, then you are done. If you plan to paint the block wall, you will need to “point” the wall. This is a smooth line that is placed into the mortar joints using a special tool called a pointer. As you work your way down the joint with the pointer, wipe off and excess with a wet sponge. Wipe up any excess mortar off of the slab or ground and you are done. Enjoy your new concrete block wall.