How to Work with Concrete Block

Every great home improvement plan starts with the basics. Learn how to set a solid base for a concrete block wall and lay out a strong foundation.

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Concrete blocks are five or six times larger than bricks, so you might think that setting blocks would be about that much easier. But the blocks are heavier than bricks—about 40 pounds—and require more mortar, so there's little time or effort saved.

Have the blocks delivered as close as possible to the work site, then set them along the footing so they're readily accessible. You can build a block wall by yourself, but one or two helpers will make the job easier.

Before you start, become familiar with block terminology. The concrete that forms the block is called the web. The cavities within the block are called cores.

A stretcher block is the common block with ears, or flanges, on the ends. Stretcher blocks make up the middle of a wall between end blocks and corner blocks. Leads are the built-up corners of a wall and are three or four courses high. You'll build leads first, then fill in between them.

Preparation Tips

Block walls require careful planning, just like any other masonry structure. If possible, plan the length of your wall so it's divisible by 16 inches (the length of a standard block and mortar joint) to minimize cutting. Since most block walls are later faced with brick or another material (the block won't show), use a standard running bond. It's easy and strong.

Build the wall on a concrete footing that's twice as wide as the block and as deep as local codes require. Even if reinforcement is not required, embed 32-inch lengths of rebar vertically in the footing at 32-inch intervals. The rebar extends into the cores when you set the blocks.

How to Lay Concrete Blocks

Before you apply mortar, lay the first course of blocks in a dry run, spacing the blocks with 3/8-inch plywood. Since you'll need some method for keeping the block square to the footing, either snap a chalk line on the footing along the edges of the block or 1-1/2 inches away from the edges. Once you've set the block, you can use a 2x4 to keep the first course spaced on this line. Or you can set stakes with mason's line to align the outside faces.

Concrete block webs are wider on one side. The wide side should face up because it provides a larger bed for the mortar. This reduces waste, minimizing the amount of mortar that falls off the web. It's also easier to handle the blocks when you grip the wide side. To save time, distribute the blocks along the job site with all the wide sides up.

Do not wet the blocks before installing them. Wet blocks expand, then shrink when they dry. If it rains or rain threatens, cover the blocks.

Spread mortar only on the outside edges of the block (a technique called face-shell bedding), not on the cross web. Applying mortar to the cross web is difficult, wasteful, and not necessary when building a wall in the landscape. An exception is when laying reinforcements.

On ends without corners, every other course after the first one should start and end with a half-block

Concrete Footing: Build a Solid Base

Block walls must be built on a solid base. Poured concrete footings for walls should be twice the width of the wall, flush with the ground, and as deep as local codes require. Building codes might also call for concrete reinforcement.

How to Make a Story Pole

A story pole helps you space the courses more quickly. To make one, cut a piece of straight 2x4 to the height of the finished wall. Then mark the courses on the board, separating them by 3/8 inch for mortar joints.

Step 1: Make Lines

Set a block at each end of the footing and center the width of each block on the width of the footing. Mark the edges of the block on the footing and snap chalk lines on the surface of the footing. Make sure your chalk lines extend to the ends of the footing.

Step 2: Space Blocks

Starting at one end of the footing with either an end block or half-corner block (depending on the length of the wall), set blocks without mortar. Place the edges on the chalked lines, spacing them with 3/8-inch-wide plywood. When you set the last block, snap perpendicular chalk lines to mark the ends of the row.

Step 3: Navigate the Corners

If your wall turns a corner, establish the corner with your layout lines. Then start the second leg of the trial run with a full corner block. Check the corner with a framing square. Lay out the rest of the blocks along the chalk lines.

How to Establish Corners

Use your batter boards and mason's lines to mark the corners of the wall on the footing. Drop a plumb bob from the intersection of the lines and mark the footing clearly. Then snap a chalk line between your marks. Check the corners for square using a 3-4-5 triangle or framing square, and adjust as needed.


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