How to Build Corners

Corners & Angles vs. Curves

Retaining wall with corners

Corners and Angles typically require custom cutting of the blocks. Try to design curves instead. Angled retaining walls are not as stable as curved retaining walls.

Whenever possible we recommend using curves instead of corners for a smooth flowing look to your landscape. If you need to use corners in your design, follow the instructions below:

Our example uses an AB Jumbo Junior, but can be used with any block.

Inside Corners

Remove raised front lip from block

Remove 1/3 of raised front lip from block

Modify retaining wall blocks to make corner

Remove raised front lip of block

Inside corners are easily constructed using standard Allan Block units. By removing part of the lip with a chisel or saw, the blocks can be overlapped for a strong interlock. If your retaining wall needs reinforcement, follow the instructions for adding grid to corners.

Using your saw or chisel, remove the raised lip from one block, and 1/3 from the left side of another. Set them in place at the beginning of the base course.
Locate the adjoining retaining wall so that the raised lip on the modified block is lined up with the raised lips on the opposite retaining wall. Finish installing the entire base course in both directions.
Modify two more blocks, this time remove the raised lip from one block, and the right third from another. Use these blocks to start the second course.
Continue the process to the top of the retaining wall, alternating as you go.

Cut caps at 45 degree angles

Cut caps at 45 degree angles to complete the inside corner and give the retaining wall a custom finished look. It's a good idea to secure caps with a high strength construction adhesive once they are all cut.
More options for finishing your retaining wall.

Video: Build a Retaining Wall Inside Corner

Outside Corners

Place corner block and build out in both directions

Alternate the corner block direction

Finish wall with capstones

Outside corners take more time and skill, but AB Corner Blocks are all you need to make an outside corner. Always build your retaining walls by starting at the corners and working out. AB Corner Blocks are manufactured with a 12° (Ref) setback. With some minor adjustments, the blocks can work with any setback. See AB Tech Sheet #298 (Using the One Piece AB Corner Block) for more details.

Set the first corner block in place and install the two perpendicular base courses. Level, backfill and compact.
Place an alternating corner block on the second course and set the entire second course of block in both directions. Level, backfill and compact again.
Repeat as often as needed to the top of the retaining wall.

Cut caps at 45 degree angles

Cut caps at 45 degree angles to complete the inside corner and give the wall a custom finished look. It's a good idea to secure caps with a high strength construction adhesive once they are all cut.
More options for finishing your retaining wall.

Video: Build a Retaining Wall Outside Corner

Corners with Reinforcement

Installing Geogrid on Inside 90° Corners

Geogrid on Inside 90° Corners

AB retaining wall with corners

On inside corners additional geogrid is required to extend past the end of the retaining wall 25% of the completed wall height.

Roll out the AB Reinforcement Grid behind the blocks, keeping the edge of the geogrid tight against the front lip of the blocks. Extend the geogrid past the inside corner by at least 25% of the wall height in one direction.
Place an alternating corner block on the second course and set the entire second course of block in both directions. Level, backfill and compact again.
On the next course of block where geogrid is required extend the geogrid past the inside corner in the opposite direction. Never place geogrid directly on top of another layer of geogrid.

Geogrid on Outside 90° Corners

EXAMPLE:
- Finished wall height is 1.8 m, divide by 4 which equals 0.45 m.
- The length the geogrid will need to extend past the corner is 0.45 m.

Installing Geogrid on Outside 90° Corners

Each side of the corner must be reinforced independently from each other.

Roll out the AB Reinforcement Grid to the outside corner in one direction. Never place geogrid directly on top of another layer of geogrid.
On the next course of block where geogrid is required, lay the next layer of geogrid perpendicular to the previous layer. Using AB Reinforcement Grid you will not need a layer of geogrid on every course due to its biaxial strength.