Ask two contractors what a retaining wall should be built from and you will often get two confident, opposite answers. Both can be right, because the two systems solve the same problem by different means: one resists the soil by being a single stiff element anchored at the bottom, the other by becoming part of a reinforced soil mass. Which one suits a job usually comes down to the site rather than to preference.
Two ways to resist the same push
A poured concrete wall is monolithic. Steel is tied into a footing, forms go up, concrete is placed, and the finished wall works as a cantilever, resisting the soil in bending with its strength concentrated at the base. A segmental block wall has no mortar and no continuous footing. It is a facing of interlocking units on a compacted aggregate base, and above modest heights it is tied back into the soil with layers of geogrid. The soil behind it stops being a load and becomes part of the structure.
What the site decides before you do
Access decides more than aesthetics. A poured wall needs forms, rebar, and a concrete truck with reach, and on a tight urban lot with a narrow side yard that alone can rule it out. Segmental units are placed by hand, which is why they suit back gardens with no equipment access. The other site question is space behind the wall: geogrid needs a reinforced zone extending back from the face, often around seventy per cent of the wall height. If there is a property line, a foundation, or a driveway inside that zone, the reinforced-soil approach is off the table and a cantilever wall becomes the answer.
Where segmental block earns its keep
Block goes up fast, needs no cure time before backfill, tolerates minor settlement without cracking because the joints are dry, and can follow curves easily. It also builds in drainage: the open joints let water weep through the face rather than accumulating behind it, provided the aggregate zone behind is built correctly. For garden terracing, planters, and walls up to moderate heights, it is usually both cheaper and more forgiving.
Where a poured wall is the only sensible answer
Once the wall is also doing another job, poured concrete tends to win. Anything that forms part of a basement or foundation, anything supporting a structure above, and anything where the reinforced zone cannot be excavated is cantilever territory. A poured wall also takes a surcharge more gracefully: a driveway or parking area right at the top of the wall is a load the engineer can design a cantilever section for without needing to own the soil behind it.
Both fail the same way, and it is not the wall
The debate about materials distracts from the thing that actually causes failures. Saturated backfill exerts substantially more pressure than drained soil, and most collapsed walls of either type were drowned before they were overloaded. Clean angular stone behind the face, a perforated pipe at the base with somewhere to discharge, filter fabric between the stone and the native soil, and compaction in lifts as the backfill goes in: that specification matters more than the choice between block and concrete. A cheap wall usually saves its money in exactly that zone, where nobody can see it afterwards.
Frequently asked questions
Which is cheaper to build? At garden heights segmental block is normally less expensive, mostly because it needs no forming, no rebar tying, and no concrete delivery. As height increases the gap narrows, since the geogrid, the excavation for the reinforced zone, and the compaction effort all grow with it.
Does a block wall need a footing? Not a concrete one. It needs a compacted aggregate leveling pad, typically set below finished grade so the bottom course is buried. That pad has to be flat and well compacted, because every course above inherits whatever error is built into the first one.
Can a wall be repaired without rebuilding? Sometimes. A poured wall with a hairline crack and no movement can be sealed and monitored. A block wall bulging in the middle of its height is usually telling you the reinforcement or the drainage is inadequate, and that is normally a rebuild of the affected section rather than a repair to the face.