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How to Build an Interlocking Wall System

If you have a steep hill in your backyard, why not use it to your advantage?

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Step 1: Measure the Footing

Before beginning construction, measure out your wall's footing. Set up stakes and run a string line between them. If your wall is going to line up against a house or any other structure, use a square to make sure the string is square to the house. Mark the line on the ground with marking paint. This will tell you where to dig the footing. You'll also want to establish the wall's height before beginning construction. Your retaining wall should be high enough that the ground behind it is level. However, the high ground should also be pitched slightly so that rainwater will run downward.

Step 2: Dig the Footing

For a wall that measures around three feet, you'll need to dig a deep base. Footing depths vary with the height of the wall and type of system used, so check your product's specifications. Eventually you'll want your first row of blocks to lay four inches below grade, with 8 to 12 inches of gravel beneath that. So you'll be digging down 12 to16 inches total. Use a front-loader or skid steer to dig the trench for the footing. Your first layer of gravel will be about six inches of crusher run. Bring in a crusher run and spread it into the footing. Then use a plate compactor to compact the crusher run in three-inch increments. On top of that, spread in six inches of 3/4-inch crushed stone, which will stabilize the blocks and provide drainage. Make sure the base is level, then compact the 3/4-inch crushed stone with the compactor (again in three-inch increments).

Step 3: Set the Stone

For the look of this project, use concrete blocks that have been tumbled for a natural stone appearance. The blocks have a tongue-and-groove system for easy stacking. The system also includes blocks of different seizes to create visual interest. As you set the rows of stone, avoid laying the stones so as to create continuous or connecting joints. Alternating or "breaking up" the joints will give you a stronger wall structure.For the first row of cement blocks, make sure to use the larger blocks for added support, and set them flush with each other. There will be a tongue on the bottom of the blocks in the first row, so you may need to adjust the gravel underneath in order to set them evenly.When you set a concrete block, give it a few whacks with a rubber mallet to secure it into place (Image 1). As you set the first row, be sure to keep checking that you are level front to back and side to side (Image 2). If you take your time leveling the first row, then the other rows will go easier. The next row will simply lock into place, thanks to the blocks' tongue-and-groove system (Image 3).

Step 4: Add Drainage

Before building any steps, you'll need to add some drainage for the wall. You'll be laying perforated pipe along the wall, but first you need to wrap it in landscape fabric, which will allow water, but no dirt, to get through. You'll need a sharp knife to cut the fabric. This will provide drainage as water seeps through the gravel behind your wall system, eventually entering the perforated pipe and draining away from your house. Lay the perforated pipe behind lowest point of wall, and pitch it away from the house. Then surround the pipe with 3/4-inch crushed stone. To separate the gravel from the soil, line the backside of the wall with landscape fabric. The landscape fabric will prevent dirt from seeping into the layer of gravel and clogging up the wall's drainage system. To spread the layer of landscape fabric, first set down metal stakes (or metal rods for taller projects) into the ground, spread the length of the wall. Stretch your landscape fabric so that it runs the length of the rods. With the landscape fabric held up by the rods, spread gravel on the side facing the wall, and then spread dirt on the other side. As you build up the wall, you'll continue to add gravel and dirt until it's just under the top tier.

Step 5: Build the Steps

For setting your second row of blocks, first set down a corner block where you want your steps to begin. Measure out the length of your treads, and then put in a second corner block on your wall that accounts for the length. Now you have the opening marked out for your steps. Keep in mind that the product will determine the length of a step.Returns are the corners at both the wall and the steps. To set the returns at the steps, first take a wall block, and line it up with each corner block that you had set in the wall earlier. Your return should now be at a 90 degree angle to the wall. Make sure the stone is level from front to back, and side to side, and then set it on the gravel that has been build up under the first row of blocks. With the first returns in, you can now work on the risers for the first step.The riser is the face of each step, and will support the tread. Dean and Derek's step and returns system uses 10-inch riser modules and 14-inch step/tread modules to create stair units.Sometimes it may be necessary to cut a riser piece in half, so that the riser joints do not line up with the tread joints, creating an unattractive stacked look. To do so, mark a line where you want to split the stone. Then use a stone hammer and iron chisel to split the stone. (If you don't want to use a hammer and chisel, you can rent a block cutter from a local tool rental company.) Always be sure to wear safety glasses when cutting any masonry. Set the risers, and use concrete block adhesive to secure them into place. With the first row of risers complete, follow up with the treads. Squeeze concrete block adhesive onto the tops of the risers, and then secure the treads on top of them. Now your first step is complete, and you can move on to the second step.

Step 6: Build Up the Wall

As the steps go in, you can start to build up the bulk of your wall. Don't forget to keep breaking your joints, and add gravel so that it's always just under your top tier as you build up (Image 1). As you work, it's important to keep compacting your gravel. In order to do so, use a hand tamper (Image 2), or if you want to work more quickly, use your plate compactor. Remember to keep the landscape fabric as a barrier between the gravel and the dirt behind it. The fabric is especially important behind the steps, because they are not as strong as the rest of the wall. As you build up the wall, keep constructing the steps and returns so that they're level with the wall.

Step 7: Add Geogrid

Geogrid will stabilize the backfill behind the wall, so that the power of the backfill is not constantly pushing up against the tongue-and-groove wall. The height necessary for geogrid can vary for different wall systems. For a tongue-and-groove system, you don't want to go higher than two feet without it.Add geogrid once your wall is built up to a height of about 1-1/2 feet. The length of the geogrid should be about 90 percent of the height of the wall (in this case, 30 inches for the 36-inch-high wall.)Place the wall blocks on top of the geogrid to secure it, and continue to build up the height of the wall. On top of the geogrid, lay additional landscape fabric. Then bring in more crushed stone on top of the fabric. The gravel will eventually go up to the mulch line, just a few inches below the top the wall. Lay more landscape fabric on top of the crushed stone.

Step 8: Cap the Wall

Before setting any caps, lay them out dry first. When you dry-lay the capstones, you'll probably find that you need some cuts. If you need to cut, then make a mark on the block with a pencil, and split the block with your hammer and chisel. Hide any cuts in your cap adjacent to the corner block. When making cuts, try to avoid making sliver cuts — thin cuts that tend to draw the eye and can look unattractive. If a sliver cut does occur, you can help lessen the visual problem by making a cut in the stone next to it. In that way you end up with two adjacent cuts, but together they won't be as visually obtrusive. Before gluing any caps, take a bristle brush and clean off the tops of the stones underneath the caps. You want all the dirt off to make sure that the adhesive bonds the wall product to the adhesive product. As the final step in the new retaining wall, use a caulking gun to lay three lines of adhesive across the stone and then lay down the cap.

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