· by Michael Blair, Nashville's Masonry
Both build sound walls. The differences are in cost, how they handle height, and how they are reinforced — and in all cases the drainage behind matters more than the face.
Segmental block
Engineered units that interlock, designed to be built with geogrid reinforcement extending back into the slope on taller walls. Predictable, well documented and straightforward to build correctly.
It reads as manufactured, which suits some settings and not others.
Natural stone
Dry-stacked or mortared. A well-built dry-stack wall drains freely through its face, which is a genuine advantage on Middle Tennessee clay, and it looks better in most garden settings.
It costs more, depends heavily on the skill of the builder, and is harder to engineer for height.
- Segmental block: predictable, engineered, geogrid on taller walls
- Dry-stack stone: drains through the face, needs a skilled builder
- Mortared stone: appearance of stone, needs drainage like block
- Any wall over about four feet: engineering and a permit
Drainage decides longevity either way
Clean angular gravel behind the wall, a perforated pipe at the base daylighting downhill, and geotextile keeping soil out of the gravel.
Walls that fail here overwhelmingly failed on drainage rather than on the units, whichever material was used.
Height and permitting
Above roughly four feet, Metro generally requires a permit and engineered drawings, and any wall carrying a surcharge such as a driveway above it needs engineering regardless of height.
Terracing two shorter walls instead of one tall one is often cheaper and better looking, provided the spacing is enough that they do not surcharge each other.