I’m building a curved retaining wall using stackable blocks. When I get to the second course, the joints are off by several inches. How can I correct this? -Hub
When building a retaining wall using wedge shaped stackable blocks, the lip on the back causes each course to step back slightly from the one below. That means that the radius of curves and the diameter of circles will become progressively tighter and smaller with each course of blocks laid.
When building a straight wall, the setback doesn’t pose a problem; but when curves or circles are involved, it causes the joints in each course to off center from the course below, since the length of the wall is less. The greater the setback, the more obvious the joint alignment offset.
To keep the joints in each course exactly centered on the course below, you would need to cut the blocks in each row a bit shorter than the blocks in the course below, or settle for the blocks being off center.
If the radius of the curve becomes so tight that the angled edges of the blocks touch, you would have to cut the edges to a sharper angle to prevent gaps in the joints from showing. Your other option would be to start with a larger radius curve on the bottom course, so the edges of the blocks will still meet at the top without cutting.
For help determining the correct radius for a stackable block retaining wall, contact the block manufacturer. Each block system is different, and most manufacturers have brochures or online guides that give the minimum radius for curved walls. Many will even tell you how large the radius of the bottom course should be, depending on your wall height.
Here’s an example from retaining wall block manufacturer Allen Block.