How Serious Is a Crack in My Basement Wall?
Short answer: it depends on the crack. Some are cosmetic and some are a warning sign. Here is how to tell the difference before you spend money or lose sleep over it.
Cracks that are usually not a big deal
Thin vertical or near-vertical cracks in a poured concrete wall are the most common kind, and most of them are shrinkage cracks. Concrete shrinks slightly as it cures, and it often cracks at the weakest point, frequently near the middle of a wall or beside a window. If the crack is narrow, the two sides line up flush, and it is not getting longer or wider, it is usually just a path for water and is sealed with an injection.
Hairline cracks in the corners of a poured wall and short cracks that have been painted over for years without changing are also generally low concern.
Cracks that should be looked at
- Horizontal cracks running along the wall, especially in block, which usually mean soil pressure from outside
- Stair-step cracks that follow the mortar joints in a block or brick wall, which can point to settlement on one side
- Cracks wider than about 1/8 inch, or cracks that are wider at one end than the other
- Cracks where one side sticks out past the other, so you can feel a lip when you run your hand across
- Any crack that is visibly longer or wider than it was a few months ago
- Cracks that appeared suddenly along with sticking doors or new drywall cracks upstairs
A crack in any of those categories is worth a professional inspection. It does not automatically mean a big repair, but it means the wall may be moving, and movement is what turns a minor issue into a major one.
How to check if a crack is active
Mark the ends of the crack with a pencil and write the date. Measure the width at the widest point and note it. Check again in a month or two, and after a heavy rain and after a dry spell. If it has not changed, the movement is likely old and stable. If it has grown, it is active and should be inspected.
You can also look at the edges. A fresh crack has sharp, clean edges and clean concrete inside. An old crack is dirty, painted, or has debris packed into it.
What it means for water
Even a cosmetic crack becomes a leak once the soil outside is saturated. Water under pressure finds the crack and tracks through the full thickness of the wall. Sealing it from the surface with hydraulic cement or caulk rarely lasts because it does not fill the depth of the crack. A full-depth polyurethane injection does.
If water is coming in at several points or along the joint where the wall meets the floor, one crack repair will not solve it, and an interior drainage system is usually the better answer.
What to do next
If your crack is in the low-concern group and only lets in water, a crack repair handles it. If it has any of the warning signs, or you are not sure, a free inspection will tell you whether the wall is moving and what your options are.
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