Things You'll Need
Walls are built to stay strong over a long period of time, but a changing landscape of harsh weather conditions can cause a wall to weaken. Building a retaining wall in front of an existing wall can help protect the old structure while giving you double the protection. Installing a retaining wall properly is essential; failure to do so can lead to the wall crumbling, which may cause injury. Do not attempt to build a retaining wall that is over 4 feet in height without consulting a contractor or your local building department.
Dig a trench that is 1/10 the final height of the retaining wall. Make the trench so it is 12 inches away from the original wall.
Add 1 inch of sand to the trench to level the soil out. Compact the soil with a tamper to prevent settling.
Lay down a layer of concrete blocks into the trench. Set a carpenter's level on top of the blocks to ensure they are level.
Lay a new level of concrete blocks on top of the first layer 3/4-inch back from the front of the first layer. This creates a step look to the wall.
Insert a retaining pin into each concrete block and hammer it into the block below with a rubber mallet.
Pour gravel between the retaining wall and the wall behind it after each layer is set down. Compact the gravel. The gravel allows drainage behind the wall.