Diagnostic Guide
Foundation crack types explained
A crack is a record of what the building did. Direction tells you the mechanism, taper tells you the geometry, width tells you the magnitude, and a dated second measurement tells you whether it is finished.
Vertical cracks in poured concrete
Thin, roughly vertical cracks in a poured foundation wall are usually shrinkage from the original cure. Concrete loses volume as it hydrates and the wall cracks where it is restrained. These typically appear within the first year of the house's life, run from the top of the wall part way down, and stay the same width forever.
They matter for water, not for structure. A shrinkage crack below grade is a path for moisture into a basement and is a candidate for injection. If a vertical crack is wider than about an eighth of an inch, tapers noticeably, or has offset faces where one side sits proud of the other, it is no longer a shrinkage crack.
Diagonal cracks off door and window corners
The classic settlement signature. Openings are the weak points in a wall, so when a building racks, the stress concentrates at their corners and the crack runs away at roughly forty-five degrees. In drywall it looks like a tear from the corner of a door frame heading toward the ceiling.
Read the taper. A diagonal crack that is wider at the top indicates the ground below has dropped, opening the wall like a hinge from the bottom. Wider at the bottom points at heave, with the middle of the structure pushed up. In the Grand Valley both occur, and the distinction determines the repair.
Stair-step cracks in block and brick
Masonry cannot crack diagonally through the units, so it cracks around them, following the mortar joints in a stair pattern. Same mechanism as the diagonal crack, different material.
Two details are worth noting. First, whether the crack is confined to the mortar or has broken through the units themselves; through-unit cracking indicates more force. Second, whether there is any offset perpendicular to the wall face. A stair-step crack with the two sides sitting flush is a vertical movement problem. One with the sides offset outward is a wall being pushed as well as dropped.
Horizontal cracks near mid-height
The one that changes the conversation. A horizontal crack roughly halfway up a basement or stem wall means the wall is bending under lateral load from the soil behind it, not settling. It is a bending failure, and it usually comes with a measurable deflection: hold a string line or a long level against the wall and the middle stands proud.
In this valley the water behind that wall is generally identifiable. A downspout, a sprinkler zone, a lateral, or slope drainage arriving from above. The bowing wall guide covers what the repair options are and how deflection decides between them.
Cracks in a slab floor
Slabs crack routinely and most of it is nothing. Hairline map-pattern cracking is shrinkage. A single crack running across a room, particularly with the two sides at different heights, is a movement crack and worth measuring.
On a slab-on-grade house in expansive soil, the specific thing to look for is a raised centre. Run a long level or a marble across the floor. If the middle of the house is high, that is heave rather than settlement, and no amount of perimeter piering will address it.
Cracks with efflorescence or staining
The white crystalline bloom on a wall next to a crack is efflorescence: salts left behind by water that has passed through the concrete and evaporated. It is not structural, but it is proof that the crack is a water path and that water is present behind the wall regularly enough to keep depositing salts. That is useful diagnostic information regardless of what else is happening.
Spalling and softening rather than cracking
Different failure entirely. Where a stem wall is flaking, crumbling, or has rebar showing through softened concrete, the concrete itself is deteriorating rather than the house moving. In gypsum-bearing soils, and several soil series mapped under Grand Junction carry substantial gypsum, sulfate attack is a plausible mechanism: sulfate salts react with the cement paste and degrade it from within. Piering a wall that is chemically deteriorating does not fix the wall.
How wide is too wide
| Width | General reading |
|---|---|
| Hairline to 1/16 inch | Usually cosmetic or shrinkage. Worth a dated photograph and nothing else. |
| 1/16 to 1/8 inch | Worth measuring and dating. Investigate if it tapers or has offset. |
| 1/8 to 1/4 inch | Worth an elevation survey to see what the floor is doing. |
| Over 1/4 inch, or any visible offset | Structural attention warranted regardless of other symptoms. |
These are rules of thumb rather than thresholds. A quarter-inch crack that has not changed in twenty years is a different situation from an eighth-inch crack that appeared last spring.
Establishing whether it is still moving
This is the question that decides everything, and it costs nothing to answer properly. Five steps, over a year:
- Mark each end. A light pencil line across the crack at each end, with the date beside it, shows whether the crack is lengthening as well as widening.
- Measure the width. At the widest point, with a crack comparator card or a tape. Record the figure and the location.
- Photograph against a scale. A ruler or a coin in frame, taken from a spot you can stand in again.
- Repeat across the seasons. Late winter, mid summer, late autumn. The irrigation season and the monsoon both shift soil moisture here, so a full annual cycle is the meaningful interval.
- Compare. No change across a year points at historical movement. Progressive widening points at an active condition worth measuring properly.
A dated baseline is also the single most useful document to hand a contractor or an engineer, because it turns a subjective impression into evidence.
When to stop watching and start measuring
- Any crack that has widened measurably between two dated readings.
- Any horizontal crack in a foundation wall.
- Any crack with faces offset out of plane.
- Cracking accompanied by a door or window that has changed operation.
- A floor that reads noticeably out of level where it did not before.
- A home inspection or a sale timeline that needs the question settled now.
At that point the next step is an elevation survey, which converts the whole picture into numbers.