How to Install Caps on Retaining Walls

Set a cap on one end of your retaining wall. If the manufacturer does not make corner caps, you will notice that one of the cap's exposed edges is smooth. Make a small chalk mark on the cap's smooth end to indicate this is the side to cut off.

Rent a guillotine cutter from your local hardware store. Measure the cap's width and divide it in half. Draw a chalk line down the block, cutting it in half, using a level as a straight edge. Position the cap on the guillotine cutter's table so the blade will cut through the chalk line. Turn the guillotine cutter's handles to secure the cap in place and pull on the lever.

Remove the cut cap from the guillotine cutter. Insert a tube of masonry adhesive into a caulk gun. Apply two thick beads of the adhesive along the top of the retaining wall, on the end where you will place the cut cap.

Set the cap into the masonry adhesive on the retaining wall. You can either adjust the cap so its edges are flush with the retaining wall block's edges or you can pull the cap forward to extend 1 inch over the retaining wall block.

Apply more beads of masonry adhesive on the retaining wall, next to the cut block. Set the next cap on the wall, centered over the two retaining wall blocks beneath it. Adjust the cap so its front edge lines up with the first cap's front edge. Continue to secure caps to the retaining wall with masonry adhesive down the retaining wall's entire length until you can no longer fit a full cap on the wall.

Test fit the final cap on the retaining wall. Divide the cap's width in half and cut it with the guillotine cutter, the same way you cut the first cap from Step 2. Apply construction adhesive on the retaining wall's end blocks and set the cap in place. Adjust its front edge to line up with the rest of the caps.