How to Build a Retaining Wall with a Gravel Foundation

Preparing the Area

• Before you place your first block, it is important to map out the dimensions of the retaining wall and to prepare the area. Drive wooden or metal stakes into the ground in the position of the corners of the wall and stretch colored string between the stakes to represent the wall. Once you have mapped out the location of the wall, you should dig out the area to a depth of 8 inches and fill the resulting trench with about 4 inches of gravel. To create a solid foundation for your wall, rake the gravel out evenly then compact it with a hand tamper and check it with a level.

Laying the First Blocks

• Once you have established a firm gravel foundation, you can begin to lay the first stones or blocks for your retaining wall. The type of stone or block you choose for your retaining wall is simply a matter of taste, but large concrete blocks designed for retaining walls are among the easiest materials to use if you are doing the job yourself. To begin laying blocks, start at one end of the wall and set the first block in the gravel, aligning the face of the block with the edge of the trench. Continue placing blocks next to each other, checking to make sure they are level as you go and tapping them with a rubber mallet if adjustments are needed.

Installing a Drainage Pipe

• Building your retaining wall on a solid gravel base will not necessarily be enough to make it last. If you do not install a drainage pipe, rainwater will build up in the soil behind the wall, which may cause the blocks to shift and the wall to sag. Cover a corrugated drainage pipe with a mesh sleeve and run it behind the first row of blocks, past the end of the wall, where the water can drain. The sleeve will keep sand and soil from clogging the pipe and preventing proper drainage.

Building the Wall

• Build up your retaining wall, using the blocks you have chosen, stacking new rows on top of the row beneath and checking to make sure each new block is level. If the blocks you have chosen are hollow, fill their concrete cores with excess gravel from the foundation to provide extra support for your retaining wall. As you build, cover the drainage pipe with gravel as well. The ideal height for retaining walls is 3 feet or less, so keep this in mind as you add new layers of blocks to your wall.

Finishing the Wall

• The final step in building a retaining wall with a gravel foundation is to install the capstones. Capstones are simply large flat blocks designed to be installed on top of a wall to give it a finished look. Before you lay the capstones, brush away any dust or gravel from the top layer of blocks and apply some concrete adhesive to the tops of the blocks using a caulking gun. After laying each capstone, press the block into the adhesive to create a tight seal. Once the adhesive dries, you will be able to fill the area behind the retaining wall with soil and continue with your landscaping plan.