How to Build a Retaining Wall

Here are some things to know before you start buying material and building a retaining wall:

• Call 811 before you dig. Stay safe and locate underground utility lines.
• Depending on the wall’s height and your location, you may need a building permit to install a retaining wall. Check your local building codes and restrictions, as well as your homeowner's association (HOA) restrictions.
• Choose a DIY-friendly building material. Retaining walls can be made from wood, bricks, natural stones or concrete blocks. For DIYers, it’s easiest to use concrete retaining wall blocks that interlock. Interlocking blocks fit together and add extra security to the wall.
  For retaining wall ideas, visit your local store for inspiration.
• When the soil behind a retaining wall gets wet, it exerts much more pressure and weight against the wall. To relieve some of this pressure, your retaining wall needs proper drainage. Plan to backfill the wall with well-draining gravel or sand.
• Higher walls or areas with soil that stays wet may need a drainage pipe.
  Keep in mind that clay soil retains water and sandy soil drains too easily. You'll need a well-draining soil mix behind your landscape retaining walls.
• Measure the total length of the retaining wall and the finished height. Determine how many blocks will be needed by dividing the length of the finished wall by the length of an individual block. This will tell you how many blocks per course. Then divide the total height by the thickness of an individual block. This will tell you how many courses will be needed. Multiply these two numbers to get the number of blocks needed to complete the project.
• When selecting blocks on homedepot.com, you will find a calculator for the specific block's dimensions on the product information page.
• Half the height of the first course should be below ground level for low walls. A full block will need to be underground for walls higher than 3 feet.
• When buying material, purchase 10 percent more than what you estimate you need. This will account for any estimate errors and provide extra material for cutting blocks and replacing blocks in the future.
• Plan to build your wall after a long period without rain, when the soil is dry.
• Other materials may include landscape fabric, gravel, perforated drain line, paver base, paver sand and landscape block adhesive. These items will depend on your specific situation.

• Using a tape measure, decide the length and the width of your retaining wall.
• Mark off the area with garden stakes and a mason’s line.
• Tie the line to the stakes a few inches higher than the desired height of the wall. Use line levels to make sure the string is level.
• Measure down from the string to the highest point of the wall and offset all measurements by that much. This height difference is to give room to work around the string without moving it.
• If your wall will be curved, use paint to mark the shape and location of the wall.

Safety Tip: Stay safe by wearing protective eyewear, boots, gloves and work clothes while you build your retaining wall.

After selecting the style and number of blocks, you're ready to gather all the tools and materials to complete the retaining wall.

• Retaining wall blocks
• Paver base
• Gravel
• Topsoil
• Mulch
• PPE, including boots, gloves, and safety glasses
• 4 or 6 foot level
• Torpedo level
• Line level
• Grade stakes and mason's line
• Ground-marking spray paint
• Measuring tape
• Rubber mallet
• Trenching shovel
• Hand tamper
• Rake
• Hammer
• Masonry chisel

The success of your DIY retaining wall depends on a level base. Most of the time building the wall will be dedicated to making the level base. To create a solid foundation, dig a trench for the first course of your interlocking retaining wall blocks. Make sure the ground remains even throughout.

• Begin digging into the ground with a trenching shovel.
• The trench should be deep enough to bury at least half the height of your first course of blocks plus 3 inches of paver base. Depending on the size of your blocks, this depth could be 4 to 8 inches.
• The trench should be twice as wide as a single block.
• Once you’ve dug the trench, compact it with a hand tamper or vibrating plate compactor.
• Pour in the paver base and compact it as well.
• Use a 4 or 6 foot level in the trench to ensure that the bottom is level lengthwise and a torpedo level to ensure it is level front to back.

Tip: The trench should account for any slopes. You may have to create steps up or down to ensure the top of the retaining wall will be level. The wall should never run parallel to a slope.

It’s time to start laying the retaining blocks on the sturdy base you just created.

• Start at the end of the trench that is lowest.
• Center the first course of blocks on the centerline of the trench.
• Position your first block, using a level. If needed, reposition it using additional base material and a striking tool like a rubber mallet to tap it into place.
• Continue laying your first course of blocks, while checking that every block is level.
• Lift low blocks with more base material and tap down high blocks with the rubber mallet.
• After you finish the first course, fill the space between your retaining wall and landscape with gravel.
• Tamp the gravel to increase the wall’s stability and durability against soil erosion.

Tip: If your retaining blocks have flanges, either dig some relief into the base to make room or use a hammer and masonry chisel to knock off the flanges on the first course blocks to ensure they sit level.

The blocks should be staggered, so you’ll need to cut the end blocks of each even-numbered course in half. For example, the second and fourth courses should have half end blocks, while the first and third courses should have full end blocks.

• Use a straight edge to draw a guideline down the middle of the block.
• Some retaining wall blocks have V-shaped notches on the backside. These notches allow you to easily cleave the block in half using a hammer and chisel.
• Use the chisel and hammer to score the lines that were marked.
• After scoring, strike the chisel harder to split the block.
• You can also cut blocks in half using a circular saw or an angle grinder with a masonry blade.
• A wet masonry saw can be rented from the Home Depot. This keeps dust down and will generally cut cleaner than other options.
• Always wear eye and ear protection and a dust or respirator mask for this step. Masonry dust is very dangerous to inhale and will injure your eyes. Please don't rely on holding your breath and the so-called "safety squint."

By installing an even first course, you’ve successfully laid the groundwork for more courses. Here’s how you lay the next levels of interlocking wall blocks.

• Brush off the first course of blocks with a broom to remove any debris.
• Start the second course of blocks with one half of the end block you cut in the previous step.
• Lay the rest of the second course blocks, interlocking them if applicable, and finish the course with the other half of your cut block.
• Check for level as you go and adjust as needed.
• Landscape adhesive may be used between rows of blocks but it usually isn't necessary unless using cap blocks.
• If you wish to lay more than two courses, you only need to cut a block in half for the even-numbered courses. Following this rule will ensure your blocks are properly staggered.
• Brush off the blocks to clear away debris before starting the next course.

If your area experiences heavy rains or the area is heavily watered, install a drainage pipe behind the wall. It may be easiest to do this when you’ve only installed one or two courses. If you live in an arid area, gravel or river rock in a bed of landscape fabric may be sufficient.

• Use a perforated corrugated pipe.
  The pipe should extend behind the entire length of the wall and drain somewhere the water can exit the area.
• Cover the pipe with a drain sleeve to keep sediment from clogging the drain.
• Pour gravel behind the wall to completely cover the pipe.
• Resume laying courses as needed.

Once you’ve laid all the courses of blocks, you can fill in the area behind the wall.

• Backfill the wall with gravel or sand. If you use sand, first cover the backside of the retaining wall with landscape fabric. This will keep the sand from seeping between the blocks.
• If you’re backfilling with gravel, you can pour the gravel after every course you lay. This will give the gravel time to settle.
• Shovel in the backfill material in small portions.
  Tamp it down as you go, ensuring there are no hollow areas
  and it settles completely.
• Backfill up until slightly below the height of the wall.
• Fill the remaining space with sod or
  topsoil for growing grass or other plants. Make sure you fill with a well-draining soil mix.

Put down a layer of capstone blocks to complete your landscape retaining wall and enhance the overall aesthetic.

• Brush off the last layer of stones and clean off any debris.
• Using construction adhesive, secure your capstones and create the top layer of your retaining wall. The block caps should overhang the retaining blocks by 1 to 1 1/2 inches.
• Replace the topsoil and sod in front of the retaining wall as needed. Consider accentuating the wall with bushes, climbing plants and succulents so that it looks like a natural extension of your garden.

Tip: If the retaining blocks and block caps aren’t clean from loose dirt and debris, the adhesive glue won’t hold properly.