Interlocking concrete block is a way to build a strong wall without mortar. Some such blocks are made with flanges that slip over the rear edge of the preceding course; others rely on a system of pins. With both types, you don't have to practice throwing mortar or setting block, but you will get an attractive addition to your landscape. The flanges slope the wall back into the slope for additional strength.
Interlocking-block walls don't require a footing, but some styles require you to set the first course in a trench to hold the bottom of the wall in place. Cut the slope back 12 to 15 inches from the rear of the trench to leave room for gravel backfill and a drainpipe -- a must for retaining walls. Save the topsoil and use any extra as fill elsewhere in your landscape.
10 to 20 hours to excavate and lay a 3x16-foot wall
Tape measure, shovel, tamper, level, circular saw, small sledgehammer, rubber mallet, torpedo level, brick set, caulk gun
Digging, designing layout, leveling and laying block
Landscape fabric, gravel, drainpipe, landscape blocks, construction adhesive
Using the line or the edge of the trench to guide you, lay the first course in the trench. The first course blocks are set backwards for many styles. Set each block with a rubber mallet. Make sure each block is level front to back and with the adjoining blocks. Use a 4-foot level to check -- shorter levels are not long enough to ensure accuracy. If you need less than a full block at the end of the wall, lay smaller blocks or trim full blocks to fit.
Set the remaining courses with the flanges tight against the back of the preceding course. Start every other course with a half or partial block so the joints are offset by at least 3 inches or the amount specified by the manufacturer's instructions. As you work, check the blocks for level. Shim the low end of a block with a small piece of cedar shingle.
After the third course of block, backfill the area between the wall and the slope with gravel, just about even with the second course. Lay in a perforated plastic drainpipe on the gravel (holes down). Let the pipe daylight beyond the edge of the wall, or run it into a French drain.
If you're not building a patio or other structure below the wall, spread and tamp the topsoil you removed from the excavation. Fill in around the base of the wall and level the soil as far forward from the base as the landscape allows. Tamp the soil and replace the sod. Water the sod frequently until it is well established.