Two cracks on the same Morris Cove house: one stepping diagonally through the mortar joints above a basement window, one running dead vertical through brick and joint alike near the middle of the long elevation. Same wall, same age, two entirely different causes and two different repairs.
Step cracking: the wall is being bent
A step crack follows the joints because the joints are the weakest path. It appears when one part of a wall moves relative to another and the wall has to accommodate a shear — most often differential settlement in the foundation.
Read the direction. The crack usually widens toward the part of the wall that is dropping. A step crack that widens as it rises toward a corner suggests that corner is settling; one that widens downward suggests the middle is being lifted, which is heave rather than settlement.
Common causes here, in order of how often I see them:
- A downspout discharging next to the foundation, softening the bearing soil on one side.
- A large tree drawing moisture from one side in dry summers.
- A footing built partly on undisturbed soil and partly on backfill — very common where an addition meets original construction.
- An old utility trench crossing under the footing line.
Vertical cracking: the wall is being stretched
A vertical crack running straight through units means the tensile stress exceeded the strength of the brick itself, not just the joint. That takes more force and it usually comes from expansion rather than settlement.
Clay brick expands irreversibly as it takes on moisture after firing — most of it in the first few years, continuing slowly for decades. Combined with thermal movement, a long unbroken wall with no movement joint will eventually crack, and it will crack in the middle of the longest run or at a change in wall height.
Other vertical crack causes: a rusting steel lintel or shelf angle jacking the masonry above it, corrosion of wall ties in a cavity wall, and frost expansion in a saturated parapet.
One more distinction worth making: a vertical crack at a corner, where two walls meet, is often neither expansion nor settlement but a wall that was never properly bonded or tied at the return. Those open slowly and steadily and they need tying rather than filling.
Horizontal cracking, briefly, because it is the serious one
A horizontal crack along a bed joint, especially in the lower third of a basement or retaining wall, means lateral pressure — soil, water, or frost pushing the wall inward. Unlike the other two, this one is a structural problem from the day it appears and it does not stabilize on its own. Get it measured, get the water and surcharge outside dealt with, and get an engineer.
What to do with the diagnosis
The shape tells you what to investigate; monitoring tells you whether to act. The method for that — gauges, dated readings, twelve months — is described in the guide to reading cracks, and the structural engineering literature on masonry distress, much of it published through ASCE, goes into the mechanics if you want it.
Repair costs once the cause is settled: repointing a static crack $12 to $30 per linear foot; helical bar stitching $60 to $140 per linear foot; installing a retrofitted movement joint $400 to $1,200; lintel replacement $1,400 to $4,000 per opening; underpinning a settling footing $1,200 to $3,000 per pier.
Frequently asked questions
My crack is both — it steps for a while then goes vertical. What is it? Usually settlement that has run into an opening or a change in the wall, where the crack switches to the shortest path. Treat it as a step crack for diagnostic purposes and look at the foundation below the stepped portion.
Can I tell the age of a crack? Roughly. Old cracks have dirt, paint, cobwebs or previous repair material in them and their edges are rounded by weathering. Fresh cracks are clean and sharp with loose dust. A clean crack in an otherwise dirty wall means recent movement.
Does insurance cover crack repair? Rarely for gradual settlement or thermal movement, which most policies exclude as wear and tear. Sudden damage from a specific event — a burst water line washing out soil, a vehicle impact — may be covered. Document the timing and the cause if you intend to claim.