Concrete Block Wall Foundations

Dig your footings. This step is central, since footings serve as the deepest part of the foundation. Generally, this part of the structure is deep underground, usually about 12 inches, and is poured concrete. For the best wall, the footings should be dug as a continuous, short wall underground following the perimeter of the house. Gravel is placed in the trench beds, and concrete is poured on top of that. Normally, metal rebar, a pole about 5/8 inch in diameter, is placed suspended in the trench as support. Most builders use wood to suspend the bars. The concrete is poured over that.

Prepare your blocks and mortar. The planning for the amount of material you will need should be done ahead of time and should be verified by a professional. For the strongest hold, your mortar mix should be at least 15 percent Portland concrete. Mortar is often “vibrated” by placing the wet mortar on a vibrating table that will push any tiny air bubbles out of the mix. This will increase its strength and minimize later settlement.

Stake out the corners. Put a pole in each corner and place a string from pole to pole, making sure the string is taut. This should be plumb, that is, level, and will serve as a guide throughout the process.

Lay your first layer of mortar. In general, this should be a thick — about 1-inch — layer directly on the concrete footers. This thickness can serve as a buffer if your row is slightly tilted. You can push bricks down onto this mortar to alter the direction and keep all the bricks level.

Wait about an 45 minutes before placing blocks. Do not place bricks immediately on wet mortar after you have laid it.

Place your first row of blocks from the corner outward. Make sure the cells of the blocks are facing upward since the rebar will be placed through the cells. If your corners are level and even, the rest of the project is much easier.

Use your level continually throughout the process. Use a layer of mortar that is thick enough to give you some play in the bricks for adjustments. The entire drying process takes a minimum of three hours. The more cement content in your mortar mix, the less time it will take to dry.

Pour concrete into the cells. Do not fill them completely, since the rebar will be stuck in the cement to hold it. The rebar should be spaced roughly every five feet and should reach as high as the wall. All cells should then be filled with cement to reinforce them. The rebar is now a permanent part of the wall.

Remove all excess mortar or concrete for all rows when you lay it. Use your trowel to scrape any excess mortar off the wall or on the top row.