Techniques for Building Concrete Blocks

Solid Base

• Any concrete block construction must start with a solid base, footings of poured concrete. In most locales, footings must extend below the frost line, the depth at which the ground freezes. A general guideline is to make footings twice as wide and twice as deep as the thickness of the wall; if you use standard 8-inch blocks, that's 16 inches deep and 16 inches wide.

Square

• Squaring forms built at the corners with 2-by-4-inch boards helps keep blocks in line. These will be set slightly outside the wall line; determine the wall line by stretching mason's twine between the forms to make an exact guideline for the blocks. For either mortar or dry-stack, lay a test course of blocks on the footings to determine how many blocks will be needed, what cuts if any may be required and where end blocks with solid faces will go. Once you've established a base pattern, set those blocks aside.

Mortar First

• The first course or row of blocks must always be set in mortar, whether the wall is to be mortared or dry-stacked. This is essential to bond the block wall to the concrete footing.The difference is that a mortared wall has mortar on the ends of the blocks to make a connection; dry-stacked blocks are simply laid with ends against each other.

Start at Corners

• Block-laying always starts at a corner, in either style. Once the first two corner blocks are in place and the corner is square, you can lay other blocks, checking with the string line and a level to make sure they are straight and level. It's best to build one layer at a time, the length of the wall or all the way around the building, then add layers. With mortar, you need to scrape off excess mortar so the joints are smooth; with dry-stack, just make sure blocks are firmly against each other without a gap.

Finishing

• Dry-stacked walls are finished with a 1/8-inch layer of surface-bonding cement, spread with a trowel, like plaster, over both faces of the wall. Both styles should be reinforced with steel reinforcing bars set through the holes in the blocks at each corner and every 4 feet in between, with the holes then filled with a concrete grout. Once that's done, any block wall is as strong as a poured concrete wall.

Decorative Covering

• Because concrete blocks are masonry, any masonry facing can be easily applied. Brick or stone facing or stucco surfacing can go right over concrete block without any special preparation. The mortar used to bond brick or stone and the cement in stucco will adhere easily to the concrete blocks. Just dampen the blocks before you apply any facing.