Why cracks leak
Concrete and block foundation walls crack for several reasons: normal shrinkage as concrete cures, soil movement, settlement, and pressure from wet soil. A crack that lets water through is a path of least resistance for groundwater pressing against the wall. That is why leaks tend to appear after heavy rain or snowmelt and slow down when the ground dries.
A leaking crack is often a sign of a drainage problem as much as a concrete problem. Sealing the crack without addressing the water outside may only move the leak elsewhere or cause it to come back. For the wider picture, see water leaking through a foundation or basement.
How to tell if the foundation is leaking
Signs include:
- Wet streaks, dripping, or beads of water along a crack
- Damp patches or discoloration around a crack
- White, chalky mineral deposits (efflorescence) along the wall
- Musty smell, peeling paint, or mold near the wall
- Moisture that appears after rain and fades afterward
Check for condensation and plumbing leaks first, since they can look similar. A wet spot near a pipe, or one that does not follow the weather, may not be a foundation leak; see the signs of a leaking pipe.
Is the crack structural?
Many hairline cracks are from shrinkage and are generally not a structural concern, though they can still leak. Cracks that call for professional attention include:
- Horizontal cracks, especially with the wall bowing inward, which can indicate soil pressure against the wall
- Stair-step cracks in block or brick that follow mortar joints
- Wide cracks, cracks wider at one end, or cracks where one side has shifted relative to the other
- Cracks that grow over weeks or months
- Cracks accompanied by sticking doors, sloped floors, or gaps around windows
Mark the ends of a crack with a pencil and date, and measure its width over time. If you see movement, call a structural engineer before any sealing. Sealing a moving crack typically does not hold, and it can hide a serious problem. If you suspect a structural issue, avoid putting stress on the wall, such as stacking heavy items against it.
Fix the water source first
- Clean gutters and extend downspouts well away from the house.
- Make sure soil slopes away from the foundation.
- Keep window wells clear and avoid watering beds next to the wall.
Even if you plan a repair, these steps reduce how much water presses on the crack.
Repair options
Hydraulic cement. A fast-setting cement that can plug an actively leaking crack. It is generally seen as a short-term or emergency measure. Typical use involves opening the crack into a groove, cleaning it, and packing the product in per the label. It can crack again if the wall moves.
Polyurethane injection. A flexible resin injected into the crack that reacts with water and expands to fill it. It is commonly used for leaking cracks, including damp ones. DIY kits exist, and professionals also use it.
Epoxy injection. A rigid resin that bonds the concrete across the crack. It is more often used for dry cracks or structural bonding, and a professional should decide whether it suits your crack.
Exterior repair. Excavating to the crack and sealing or waterproofing from outside, often with drainage improvements. This addresses the water before it enters but is a larger project.
Surface coatings. Paint or coatings alone typically do not stop water coming through a crack under pressure and may peel.
Basic steps for a DIY injection kit
These are general steps. Always follow the instructions that come with your kit. Our guide to repairing a crack in a concrete wall covers materials and mistakes in more detail.
- Put on eye protection and gloves, and ventilate the area. Injection resins can irritate skin and eyes.
- Clean the crack and surrounding surface with a wire brush, removing paint, dust, and loose material.
- Attach the injection ports at intervals along the crack as directed.
- Seal the crack surface between ports with the surface sealer from the kit and let it cure.
- Inject resin starting at the lowest port (or as the kit directs) until resin shows at the next port, then move along.
- After curing, remove the ports and surface sealer as directed, and watch the area through the next heavy rain.
If the crack keeps leaking, don’t keep adding product. Get an assessment.
What time of year is best?
There is no single best season. Many resins and cements have temperature limits on their labels, so check them. Some homeowners prefer to repair during a drier period so they can see whether the crack stays dry, while an active leak may need a quick temporary fix regardless of season. For exterior excavation, ground that is not frozen or saturated is easier to work with. A contractor can advise based on your climate.
Mistakes to avoid
- Painting over a leaking crack and calling it fixed
- Sealing a crack that is still moving
- Ignoring gutters and grading
- Using products meant for dry cracks on an active leak
- Cutting or chiseling without eye protection and a dust mask. Concrete dust can be harmful to breathe.
Does insurance cover it?
Coverage depends on your policy and the cause of the damage. Many standard policies exclude groundwater seepage and gradual leaking, and the cost of repairing the crack itself is commonly not covered. Ask your agent and keep photographs and records.
When to call a professional
Call a foundation contractor or structural engineer if the crack is horizontal, stair-stepped, widening, accompanied by bowing or door and window problems, or if the water returns after a repair. An engineer’s assessment is independent of any repair sales. If water is near electrical equipment or a gas appliance, treat that as a safety issue first and contact an electrician or utility. For leaks along the base of the wall rather than through it, see basement leaking at the floor and wall joint. After professional work, see issues to expect after foundation repair.