How to Make a 90-Degree Angle With Retaining Wall Blocks

Lay the first layer of retaining wall blocks in the trench. Use full blocks all the way from end to end. Place a 4-foot level on the blocks. Add soil back under any low areas to make the row perfectly level.

Make the first 90-degree turn by butting the side of one whole block against the back edges of the blocks around the turn. Continue down the trench with whole blocks.

Set a second row of blocks on top of the first row. When you reach the corner, place a tube of landscape block adhesive in a caulk gun and cut off the tip with a utility knife. Run two beads of caulk along the top of the first block layer. Place one bead near the front and one near the back.

Set a special corner block on top of the adhesive beads and wiggle it a bit. Special corner blocks have rough edges on all four sides and do not have an interlocking ridge, which would be noticeable from one side of the corner. Continue to lay the second row of retaining blocks alongside the corner block.

Build up a third row the same way as you did the second row. Adhere a corner block to the 90-degree bend with the landscape block adhesive. Since retaining walls are stronger with staggering joints, this corner block should turn the opposite way from the previous corner block. For example, if the second row corner block showed in the front the long way, the third row corner block should show in the front the short way.

Finish the retaining wall with caps. When you reach the turn, measure 1 inch in from the cap's smooth edge and draw a line down the cap with chalk. Line up the chalk line with a guillotine cutter's blade. Tighten the cap into the cutter and pull the handle. This produces a rough edge on the corner cap.

Apply two beads of landscape block adhesive on the final row's top surface and set the cut cap onto the adhesive. Continue to install caps along the retaining wall.