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Project Difficulty:
Moderate
Estimated
Project Time: A few hours for a small wall
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Interlocking blocks
Plastic connectors
Measuring tape
Wood stakes
Shovel
Work gloves
Safety goggles
Tamper
Gravel
4' spirit level
Perforated drainpipe
Cold chisel
Small sledgehammer
Well-draining soil, sand, or pea gravel
Adhesive
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Retaining walls are great for keeping soil from eroding down a slope or for transforming a yard into a terraced landscape. Although a retaining wall can be made using timber, stone, or brick, the easiest material for do-it-yourselfers to work with is mortarless interlocking concrete blocks specially designed for retaining walls. There are many interlocking-block retaining-wall systems available from most patio or masonry suppliers and major home centers. The individual blocks are cast to look like natural stone and come in a variety of shapes, colors, and surface textures.
Although installation techniques vary for each brand, most interlock by means of pins or clips, or joints cast into the block itself. No mortar or reinforcing bar is required. Once you provide the required footing (for most manufacturers, a compacted sand or gravel base), you simply lay up the blocks, using the appropriate pins or other fasteners to lock them together. As each course is laid, the hollow cores are filled with well-draining soil, sand, or pea gravel to add mass to the wall.
On some types, the blocks interlock so that each horizontal course is stepped back slightly from the one beneath to create a batter angle. A few brands offer alternate pin positions to create either a plumb or a battered wall. These systems also include corner blocks and cap blocks to complete the installation. Some manufacturers offer specially shaped blocks for constructing serpentine walls. The steps below outline the basic procedure for laying one common type of block. Before building any wall, check local building codes and follow them accordingly.
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1.
Prepare the Foundation
Excavate a trench along the planned wall location, and compact the soil in the trench bottom. Add a 3- to 6-inch layer of sand or gravel to level the trench and to provide drainage. The total depth of the trench will depend on how much of the wall must extend below grade on the downhill side. With some systems, at least half of the base course is buried, but check the manufacturer's instructions.
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2.
Lay the First Course
After digging the trench and filling it as instructed with gravel, lay the first (base) course of blocks, as instructed by the manufacturer. Check the blocks for level as you work. (Fig. 1)
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3.
Lay Drainpipe
Provide extra drainage on steep slopes by burying a perforated drainpipe in gravel behind the block wall. (Fig. 2)
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4.
Cut the Blocks
Use a small sledgehammer and a cold chisel to cut the blocks as needed (Fig. 3). To stagger the joints, cut the first block of the second (and then every other) course in half. Wear safety goggles and work gloves to protect yourself.
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5.
Interlock the Blocks
Proprietary block systems have different types of interlocking systems. This one uses hard plastic connectors. (Fig. 4)
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6.
Connect the Blocks
Set plastic connecting pins into holes to align blocks vertically and into formed slots to align them horizontally (Fig. 5). If required by manufacturer, fill voids in blocks using well-draining soil, sand, or pea gravel.
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7.
Finish the Wall
Top the wall with cap blocks, cementing them in place using the adhesive recommended by the manufacturer of the interlocking blocks (Fig. 6). Using dirt and gravel, backfill behind the wall.
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