How to Lay a Concrete Block Wall

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Concrete block walls are used for purposes such as building foundation walls in homes and walls in commercial and industrial buildings, among other projects. The blocks are used because of their strength, durability and fairly low cost. Building a concrete block wall is a labour-intensive, but fairly straightforward process. You can complete a small home improvement project that involves laying a concrete block wall with the help of a few friends.

Mark the area where the wall is being built by spray-painting the ground.

Excavate a trench along the spray-painted line. The trench should be twice as wide as the concrete blocks, and at least twice as deep, going deeper if needed to get beneath the frost line. Your local zoning board can tell you how deep the frost line is in your area. Renting a 1 1/2-ton excavator can make this step much easier than digging by hand.

Construct a form for the concrete by driving wooden stakes into the ground along the edges of the trench every 3 to 4 feet and nailing 2-by-4 boards to them.

Dig a small trench along one side of the form for drainage. Slope the trench so it goes down about 1 inch for every 20 feet of length.

Insert drain tile into the drainage trench, and backfill it with 12 inches of crushed gravel. Drain tile is PVC pipe that is perforated and allows water to flow through.

Place a carpenter's level across the sides of the form to check it for level. If necessary, tap down one side with a rubber mallet until it's even with the other side.

Pour the concrete into the form. For smaller projects, you can rent a small concrete mixer to handle the pours, but for larger projects, you may need to hire a contractor with a mixing truck. If you cannot complete the entire pour in one session, divide the form into smaller sections.

Screed the surface of the concrete by dragging a 2-by-4 board back-and-forth across the top of the form. This exposes low spots in the form while removing excess concrete. Add more concrete to the low spots, and screed the form again. Allow the concrete to set for at least three days.

Remove the form and backfill the area around the foundation.

Drive a wooden stake into the ground directly behind each corner of the footing, then drive a stake on both sides of the corner stakes about 2 feet down alongside the footing. Nail 2-by-4 boards along the top end of the stakes.

Tie a string to the midpoint of one of the 2-by-4s and walk it down to the opposing 2-by-4 on the next corner and tie it into position. Repeat this on each corner. The spots where the strings intersect marks the exact corner of the footing.

Place the corner blocks for the walls on each corner, lining them up so the outer corner of the block is even with the intersecting lines. Do not apply mortar yet.

Lay blocks between the corner blocks without adding mortar to determine how many blocks you need for each course. Keep a gap of about 3/8-inch between each block to account for the mortar.

Mark the outer edges of the corner blocks onto the footing, then remove all the blocks from the footing.

Mix a batch of mortar, following the instructions on the packaging.

Apply the mortar to the first corner with a trowel. Make it a layer 1 inch deep and 8 inches wide, and extend it out the distance of three to four blocks from the corner.

Set the first corner block so it's outermost corner is lined up directly beneath the strings. Check the block for level after you set it.

Lay the blocks adjacent to the corner blocks where you spread the mortar on the footing, placing mortar on the ends of the blocks as you set them. Set the blocks so they're level with the corner block and each other.

Set the blocks in the other three corners using the same process.

Finish laying the first course of blocks between the corners, applying mortar to the footing and on the ends of the blocks. Keep the blocks spaced about 3/8 inch apart, and check them for level as you lay them. If needed, cut blocks with a masonry chisel and hammer.

Continue laying the blocks until you reach the desired height. Build up the walls in the corners first, keeping them two or three blocks higher than the walls until they are at the desired height. Allow the mortar to set for the time specified on the packaging.

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