Step 1
Measure out 2 inches on both sides of the existing brick wall. Drive stakes into the ground to mark. If the end consists of a pier -- a post-like column sometimes found along the length of the wall and at the ends -- measure the distance from the wall to the pier edge and align accordingly.
Step 2
Walk the length of the wall extension desired, using a straightedge to stay true to the course of the existing wall. Sink two more stakes, properly spaced, at the end of the desired wall location. Run twine between the stakes on each side, stringing a line level in place to ensure the twine is plumb before tying it off.
Step 3
Outline the shape of the end pier, if applicable, by laying bricks on top of the ground and using a shovel to dig around the bricks to mark. Set one brick inside the future wall run. Place the next brick over the top, like an upside-down "L." Bring the next brick down from the end of the "L" and finish with another brick running back to the bottom edge of the first brick, like a backwards "L." This is a one and a half brick pier. Single brick piers, slightly smaller, require only two bricks turned sideways in the wall so the ends jut out the width of one full brick, assuming 4-by-8-by-2-inch bricks.
Step 4
Dig the outlined areas out to a minimum depth of 6 to 8 inches. The deeper the trench, the better, especially in cold climates or for walls over 3 or 4 feet high. To completely avoid destructive frost, builders often sink the footer 15 to 18 inches below the ground.
Step 5
Measure from the twine down to the bottom of the trench every 6 inches. Level the bottom, digging additional dirt out or adding packed dirt, until the measurements match.
Step 6
Spread deteriorated limestone with stabilizer or resin across the bottom, creating a 3- to 4-inch-deep layer. A premixed aggregate forms a hard pack that resists shifting. Alternatively, choose paver base, a mixture of crushed and powdered stone.
Step 7
Pack the rock with your foot and hose the surface down with water to activate the cement action in the rock. Follow with a layer of concrete. Plunge a shovel or pole down in the concrete as you pour to work air bubbles out. Cover it with plastic and leave the footer to cure for at least three or four days.
Step 8
Spread mortar along the bottom edge of each brick and set them in place on top of the concrete foundation. Butter the ends of each brick as you work so each brick will have a mortar joint completely surrounding its edges. Aim for an even layer about 3/4 inch thick. Lay a two-by-four across the top, every few bricks, and tap it with a hammer to level each brick with the surrounding bricks.
Step 9
Create piers every 9 feet of wall length and at the end of the wall if the original wall incorporates piers. Piers provide great structural support. Consider adding a pier to the first wall if desired.
Step 10
Drill a hole in the mortar in the original wall immediately above the surface of the new wall's first course. Insert a brick wall tie according to the manufacturer's instructions. Extend the free edge to rest on top of the first row of bricks and cover them completely with mortar. This will tie the new wall into the old.
Step 11
Begin each successive row with either a half or whole brick to ensure the mortar joints do not line up. Stagger the bricks along the piers similarly. Cut bricks, as necessary, holding a chisel angled slightly toward you at the desired length. Strike the brick sharply with a hammer to break it. Smooth the cut edge with gentle taps as needed.
Step 12
Work up to the wall height desired, continuing to match the existing wall's pattern. Fill in around the wall, covering some of the concrete. Pack the dirt with your feet only after the wall has cured for several days.