Backfill is the material placed behind a concrete block wall that acts as a support and a drain to divert potentially harmful moisture and water runoff from penetrating the wall and causing it to loosen and eventually fall. Backfill materials should be conducive to drainage and should shed rather than hold water. For example, gravel is a suitable backfill material and soil is not. Once your block wall has been completely erected, it is time to install the backfill.
Things You'll Need
- Landscaping fabric
- Garden shears
- Crushed gravel
Line the rear of the wall with landscaping fabric to deter plant roots and dirt from finding its way between the blocks in the wall and compromising its structural integrity. Lay one end of the fabric at the bottom of the wall and roll it out until it reaches just over the top of the wall. Use garden shears to cut the fabric and repeat the process until the entire rear of the wall is covered.
Cover the ground behind the block wall with crushed gravel, using a shovel. Fill an area approximately the same depth as the block wall and press it down firmly with a compactor. Crushed gravel has larger angles than fine gravel or sand and as a result it provides maximum support to the wall while also allowing water to pass through it quickly and easily on its way to the ground. Since the water never reaches the wall structure itself, the threat of water damage and collapse is greatly reduced.
Fill the space behind the gravel with soil excavated from the trench you dug to build the wall. Use a compactor to press the soil down as well. Continue the process until you reach the bottom edge of the top row of blocks in the wall. Use garden shears to remove any excess fabric so it reaches as near the top of the wall as possible without being visible.
Cover the gravel and filler soil with new topsoil, using a shovel. Use a compactor to press down the new soil and create a firm surface.
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