Whether you are landscaping your yard for a better look or have problems with erosion and drainage, you may be considering building a retaining wall. Concrete blocks make an excellent choice for a retaining wall as they are easy to find, relatively inexpensive and very strong. Building a retaining wall out of concrete blocks takes relatively little effort; it is unlikely to take more than a weekend.
Estimate the number of blocks the project will require. Figure one black for every foot the wall is to run. Multiply this by the number of courses you want to lay. For example, a ten foot wall that is four layers high will take 40 concrete blocks. Add some extra blocks for breakage and unanticipated problems. Buy this number of concrete blocks.
Mark where the wall will go. Dig a trench along this line as deep as one block and slightly wider than a block. Try to leave the sides as straight as possible. Using the level, determine if the bottom of the trench is level. If not, adjust it. If the wall runs down a slope then make a series of terraced walls, each lower than the next but each with a level base.
Tamp the soil with the tamper. Add several inches of gravel to the bottom of the trench. Re-level and re-tamp.
Starting at one end of the trench, lay the first block. Make sure it is level. Drive two stakes into each end of the trench, and tie strings between them, right along the top edge of the block. Level the strings before tying them off. Using the strings as a guide, continue laying the first course of blocks.
Lay additional courses on top of the first, up to the desired height. Offset each level from the next, so that each concrete block rests on two concrete blocks below it. Saw blocks in half for the gaps this will leave on the ends of some courses, using a fibrous cement cutting blade on a standard circular saw. Cut the blocks just as you would cut wood. If desired, add topper stones.
Backfill the wall. Add gravel directly behind it and fill dirt behind the gravel. Tamp down and cover both with topsoil. If using the wall to control drainage of water, place the perforated drainage pipe directly behind the wall before adding gravel.
As concrete blocks are heavy, retaining walls built out of them should be kept under four feet. Anything higher may require special reinforcement, professional assistance and building permits. Before digging, call your local utilities to determine if pipes or electrical wires are buried where you intend to dig.