We get called to look at leaning and bulging retaining walls several times a year. In nearly every case the block itself is perfectly sound — the wall failed because water built up behind it with nowhere to escape.
The force you're actually resisting
A retaining wall holds back soil, but soil isn't the hardest part. Saturated soil is dramatically heavier than dry soil, and water trapped behind a wall exerts hydrostatic pressure that pushes outward across the entire back face.
That pressure is what tips walls forward, bows them in the middle, and cracks them along the mortar lines. Build a drainage path and the pressure never accumulates in the first place.
It starts with the footing
Every wall we build starts on a poured, reinforced concrete footing below frost depth. Its width is sized for the wall's height and the load behind it, and it goes on undisturbed soil.
Walls built directly on compacted stone or, worse, on grade will settle unevenly and tear themselves apart at the joints. The footing isn't optional and it isn't where to save money.
What proper drainage looks like
A drained wall has four parts working together, and leaving any one out compromises the rest.
- Clean drainage stone backfilled the full height behind the wall
- A perforated drain pipe at the base, pitched to daylight or a drywell
- Filter fabric between the stone and the soil so fines don't clog it
- Weep holes through the wall face so trapped water has a second exit
Reinforcement through the cores
Cinder block on its own has very little resistance to being pushed sideways. Vertical rebar set into the footing and running up through the block cores, with those cores grouted solid, is what turns a stack of block into a structural wall.
Horizontal joint reinforcement between courses ties the wall together laterally. Together they give the wall the ability to resist bending rather than just standing there under compression.
When you need an engineer
In most New Jersey municipalities, retaining walls over four feet require engineered drawings and a permit. Walls holding back a slope, supporting a driveway above, or carrying any surcharge load often need engineering below that height too.
This is a good requirement. A tall wall failing is genuinely dangerous, and the engineering cost is small next to a rebuild. We'll tell you when we think a wall crosses that line, and we'd rather lose the job than build something that shouldn't exist.
Finishing so it lasts
Capping the wall keeps water out of the top course, which is where a lot of freeze-thaw damage starts. Tooled mortar joints shed water rather than holding it. Below-grade faces get parged and coated.
None of this is expensive relative to the wall. All of it is the difference between a wall that lasts decades and one you're looking at again in six years.