Concrete block is ideal for building walls to hold back the soil after you dig into a slope for a pathway, patio, or other project. Block retaining walls are generally the same as freestanding block walls -- described elsewhere on this site -- with a few important differences.
A retaining wall must provide a way to release the water that builds up in the slope behind it. Without a pressure-relief system, the weight of the water in the soil would crack, or even buckle, the wall. Weep holes -- lengths of 3/4-inch pipe inserted along the top of the first course -- escort some of the water out. The other part of the system is a plastic drainpipe covered with gravel. As water accumulates behind the wall, it percolates through the gravel into the drainpipe, which carries it off safely.
Retaining walls must be stronger than freestanding walls. Insert rebar in the footing when you pour it -- every three blocks, or at intervals specified by your local codes. As a last step, fill the cores around the rebar with mortar from the bottom to top.
20 to 36 hours for a 3x10-foot wall
Tape measure, brick set, small sledgehammer, chalk line, pencil, mason's trowel, level, mason's blocks, wheelbarrow, striking tool, story pole, shovel, wheelbarrow
Designing layout, excavating, mixing mortar, setting block
Lay out and pour footing
Concrete blocks, 2x4 stakes, 2x8 lumber, mortar, gravel, 4-inch perforated drainpipe, landscape fabric, 3/4-inch pipe
As you lay the second course of block, insert weep holes -- 3/4-inch pipe -- into the mortar every third block. Chip off a small recess in the block and trowel a mortar bed for the pipe, sloping it slightly toward the front. Then chip out a recess on the next block, butter the ears, and set the block.
After you've laid at least two courses, spread landscape fabric on the soil behind the base of the wall, temporarily laying the excess over the grass on the slope. Lay rocks on the fabric to hold it while you work. Between the rear of the wall and the slope, backfill the wall with gravel, laying perforated drainpipe on the gravel bed level with the top of the first course. Face the holes down.