Walls almost never fail because somebody chose the wrong block. They fail because water got behind them, had nowhere to go, and pushed. Everything that keeps a wall straight is invisible once it is finished.
What has to be behind the block
- A buried base course. The bottom course sits below finished grade on a compacted granular pad. A wall built on the surface has nothing resisting the toe.
- Clear drainage stone. A zone of angular clear stone directly behind the wall, so water travels down through it rather than saturating the soil against the face.
- Filter fabric. Between the drainage stone and the native soil. Without it, fines wash into the stone, it clogs, and you are back to a wall holding wet clay.
- A drainage pipe that goes somewhere. Perforated pipe at the base of the stone, daylighted where it can actually discharge. A pipe that ends in soil is decoration.
- Compacted backfill in lifts, same as any base.
- Setback and, above a certain height, geogrid — layers tying the wall into the soil mass behind it. Height thresholds are where engineering stops being optional.
How to read a wall that is going
Leaning out at the top means pressure behind it. Blocks stepping out of line mean the base moved. Soil staining or washing between blocks means the fabric is missing. A wet patch appearing below the wall after rain is actually good news — water is getting out. A wall that stays bone dry after a storm while the ground above it is saturated is the one to worry about.
When a wall is not the answer
Sometimes the slope should be re-graded instead, or terraced into two low walls rather than one tall one. Two 600 mm walls with a planted bench between them are often cheaper, safer and better looking than a single 1.2 m wall — and they avoid the engineering threshold entirely.
A leaning wall does not stabilise on its own. It gets slower, and then it gets sudden.
Free estimate
Questions about your own property?
Call or text 647-621-8592, or send a photo and the address.