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. To lay a 3x16-foot wall, expect to spend 10 to 20 hours. You’ll need to feel comfortable digging, designing a layout, leveling, and laying brick. Before you begin, call your local hotline to mark any underground utilities. Editor’s tip: Precast block is trimmed the same way other masonry materials are trimmed. If you’re using solid block, score the line you want to cut with a brick set and small sledgehammer. Repeated blows will split the block. Hollow-core blocks don’t break cleanly. Buy half blocks and smaller blocks to fit where you need them, or cut them with a masonry blade. Editor’s tip: Some blocks have pin-lock systems (see illustration, above). One of the most common employs vertical and horizontal pins. Blocks fit over the vertical pins as you lay them. After laying each course, horizontal pins lock the blocks laterally. Editor’s tip: If your wall is designed with corners, the corner blocks must overlap at the joints to tie the two legs together. Cut half blocks and alternate them with full blocks as shown, following the manufacturer’s instructions. Chisel off the lip of the block if it gets in the way. As you place the block, strengthen the bond with a bead of construction adhesive.
