How to Build Strong and Accurate Retaining Wall Corners with Allan Block Retaining Wall Systems

30 October 2025

Constructing a retaining wall is more than stacking blocks - it’s about precision, stability, and long-term durability. One of the most critical elements of any wall is the corner. A poorly built corner can compromise the strength and appearance of the entire wall. In this guide, we’ll show you how to build strong, accurate corners using Allan Block retaining wall systems, with practical tips for both inside and outside corners. 

Why Strong Corners Matter in Allan Block Retaining Wall Systems 

Corners are the backbone of any retaining wall. Properly constructed corners: 

• Provide structural stability 

• Ensure proper alignment of the wall 

• Enhance the visual appeal of the finished project 

Using Allan Block retaining wall systems correctly allows you to create interlocked corners that are strong, durable, and easy to maintain. 

How to Construct an Inside Corner 

Inside corners require careful modification of blocks to maintain an interlocked bond.  

Follow these steps: 

Step 1: Modify the First Block 
Remove half of the raised front lip from one block on each course using a diamond blade saw or chisel. This adjustment allows the next course to sit level over the corner. 

Step 2: Position the Modified Block 
Place the modified block perpendicular to an adjacent AB unit to form a solid inside corner. 

Step 3: Alternate Lip Removal on Each Course 
On the next course, remove the opposite half of the raised lip from another block. Position this block over the corner to continue the interlocked bond. 

Step 4: Repeat as Needed 
Continue alternating lip removal on each successive course. This ensures alignment and creates a strong, interlocked corner for your retaining wall. 

How to Construct an Outside Corner 

Outside corners use left-handed and right-handed corner units. Correct orientation is essential for a clean, professional finish: 

Left-Handed Corner Units 
When viewed from the front, the finished/textured end appears on the left side. 

Right-Handed Corner Units 
When viewed from the front, the finished/textured end appears on the right side. 

Step-by-Step Outside Corner Construction 

1. Start at the Corners: Begin construction at the corners and work outward in both directions. 

1. Install Base Courses: Set the first corner block, then install the two perpendicular base courses. Level, backfill, and compact thoroughly. 

1. Build Successive Courses: On the second course, place an alternating corner block to interlock with the course below. Continue laying blocks outward in both directions. 

1. Repeat Until Full Height: Continue levelling, backfilling, and compacting each course until your retaining wall reaches the desired height.  

Adapting Corner Units for Different Setbacks 

Allan Block retaining wall systems corner units are manufactured with a 12° setback, but they can be adjusted for use with different AB wall types: 

• AB Classic: 6° setback 

• AB Vertical: 3° setback 

• AB One: 1° setback 

Modification Example: 
To adjust a corner block for AB Classic, cut a 20mm notch into the short side of the block using a suitable masonry tool. This ensures a precise fit and maintains structural integrity. 

By following these steps, your Allan Block retaining wall systems corners will be strong, accurate, and visually appealing. At Colinwell, we provide guidance and high-quality products to ensure every retaining wall project is built to last.