How to Build a Stone Retaining Wall With Weep Holes

Cut 2-inch circles from fine plastic mesh screen. Center a circle on the end of a section of 1/2-inch PVC pipe that is 1 inch longer than the blocks you'll be using. Glue the ends of the mesh to the sides of the pipe. Cut a 1/2-inch strip from a rubber sheet long enough to fit around the side of the pipe and glue it on top of the mesh to hold it down and protect it from coming loose from the wear and tear. Complete one pipe in the same fashion for every three stone blocks you will lay in a row for the wall.

Dig a straight sided, flat bottomed trench along the length of the desired retaining wall that is at least 4 inches in depth lower than 1.5 times the height of a block. For example, if the block is 6 inches tall, the depth of the trench would be 9 plus 4 inches, or 13 inches. The width of the trench should be 3 inches wider than the blocks.

Tamp the earth in the trench downward to compact it and give a good footing.

Fill the bottom of the trench with 4 inches of gravel. Smooth the gravel with the edge of a shovel so it is level. Check with a bubble level to ensure the center bubble reads true along the length of the trench.

Lay the half-sized corner stone block down on one side of the trench with the front end pressed against the front end of the trench. Snug it downward so it rests securely on the gravel. Slide the second stone block next to it and strike the free side with a rubber maul to force it against the first block. Do the same with the third block. Check the three blocks with the bubble level to ensure they are level with one another.

Lay a pipe on the gravel next to the third block with the front end of the pipe even with the front end of the blocks. The screened end of the pipe is to the rear of the blocks.
Lay the next block on the gravel and snug against the pipe so the pipe doesn’t move. Continue to lay the blocks and other pipes in the same fashion until you reach the end of the trench, where you will finish with a corner block. If the number of blocks and pipes do not match evenly at the end, this is OK. Continue to check the level of the blocks every few blocks.

Mix cement powder in a bucket with water as the bag directions instruct. After the cement has achieved the desired paste-like feel, use a trowel to pour it down the gap between the blocks where the pipes are. Continue to fill in the gaps until the top of the blocks is reached. Do not overfill as this will interfere with the next block layer sliding on easily. Because this section of the wall is underground, there is no need to work hard on making it look good. The cement is only to hold the pipe in and fill in the gaps between the blocks.

Start the next row by sliding a whole block on the top of the far end bottom block. Tamp it gently with the maul to ensure it is solidly seated on the block. Continue to slide blocks on one by one until the second row is finished. The first row of blocks will be longer than the second row due to the extra space for the PVC weep holes.

Start the third row with another half-sized corner block and continue with the row the same as the others. After the third row is finished, fill in the trench behind the row of blocks with gravel up to the level of the soil. Continue to complete the wall, alternating starting every row with a half-size corner block and checking the level every few blocks.