Concrete cracks as it cures
Fresh concrete shrinks as the water in it leaves, and a slab the size of a house cannot shrink without cracking somewhere. Shrinkage cracks are thin, often hairline, fairly straight, and the same width end to end. They show up in the first year and then stop changing. Nearly every slab in the state has a few.
A shrinkage crack is cosmetic unless it lets water in. On a garage floor or a patio it can be left alone. In a basement wall or a stem wall it is worth sealing when it weeps after rain, which is what crack injection is for, but it is not a sign the house is moving.
What a moving foundation looks like
Movement cracks have a direction. One end is wider than the other, because one side dropped or rose relative to the other. They run on a diagonal from the corners of doors and windows, where a wall is weakest. In block or brick they climb the mortar joints like a staircase. And they change: a pencil mark at the end gets passed within months.
The house usually tells you before the concrete does. Doors that latched last year rub at the top corner. A window sticks. A gap opens under the baseboard, or between a countertop and the wall. The floor develops a slope you can feel in socks. Any one of these can have another cause; several together point at the ground.
Why New Mexico ground moves
Houses here mostly sit on slabs or shallow stem walls on soil that was dry when the house was built. Some of that soil is loose and collapsible: it carries weight while dry and packs down the first time water reaches it, which is why a settlement crack so often follows a new drip line, a broken pipe or a moved downspout.
Other ground is clay that swells wet and shrinks dry. A corner under a dripping canale or beside a watered flower bed can lift while the rest stays put, then settle again in a dry year, and the finishes crack both ways. Backfill around the foundation and under additions settles on its own for years.
The three cracks to act on
Horizontal cracks in a basement or stem wall come from pressure on the outside of the wall, usually wet soil, and a wall bowing inward is structural, not cosmetic. Staircase cracks through block or brick open enough to slide a coin into mean part of the wall has dropped. A diagonal crack that keeps growing while the door beside it binds means a footing or slab corner is still going down.
Those three deserve a look soon. A wide crack that is not changing, with no sticking doors or sloping floors, is less urgent and can be watched. Pencil marks at the ends with a date, and a photo with a coin for scale every few months, turn a worry into a measurement.
- Horizontal cracks, or a wall that bows inward
- Open staircase cracks through block or brick
- Diagonal cracks that keep growing while a door or window beside them binds
What the fix depends on
The repair follows the cause and how deep it goes. A slab or footing that dropped over washed-out or packed-down soil is raised with foam injected beneath it, and loose soil a little deeper can be firmed up the same way. A footing that keeps sinking because the ground well below cannot carry the house needs piers to reach soil that can.
A crack that leaks but is not moving gets sealed, not lifted. Some houses need two of these at once, and some need an engineer first: bigger pier jobs, anything that looks structural, and sales where a lender or buyer wants a letter. Whichever it is, the water that started the movement has to be handled too, or the repair holds up a house that is still being undermined.
What to photograph before you call
Good photos get you a straighter answer on the first call. Take each crack from a few feet back so we can see where it sits in the wall, then close up with a coin or a tape in the frame. Shoot the outside of the foundation at the same spot, plus whatever puts water there: downspouts, canales, hose bibs, drip lines, sprinkler heads.
Note the kind of foundation, slab, crawl space or basement, roughly when the crack appeared, and whether doors or floors have changed. If a home inspection flagged it, send those pages. From there we can usually say whether it reads as shrinkage, settlement or a job for an engineer, and what the visit will check.
In short
- Thin, even-width cracks that stopped changing are shrinkage and mostly cosmetic.
- Cracks wider at one end, climbing block joints, or still growing mean the ground is moving.
- Sticking doors, sloping floors and gaps at trim report movement before the concrete does.
- Collapsible soil, swelling clay and settling backfill do the moving here, and water sets them off.
- Photograph each crack with a coin for scale, shoot the water sources outside, and mark the ends.