Sealing leaking foundation cracks and block joints

Is it a leak or is the wall moving?

Concrete shrinks as it cures, so thin vertical or slightly diagonal cracks in a poured wall are common and usually harmless until water finds them. Those are the ones injection is made for.

Different signs point to movement: a wall that bows inward, a crack wider at one end than the other, a stair-step pattern through block that keeps growing, or doors upstairs that suddenly stick. Any of those calls for a structural engineer before anyone seals anything, because sealing a moving crack only hides it. We say so at the visit and stop there.

Injecting a poured-wall crack

The crack is cleaned and small ports are set along it, then the face is sealed over. Resin goes in through the ports from the bottom up until it shows at the next port, filling the crack through the thickness of the wall. Polyurethane foam expands to stop active water and stays flexible; epoxy cures rigid and bonds the two sides. Which one fits depends on whether the crack is wet and whether it is still opening and closing with the seasons.

Block joints and fieldstone

Block and stone do not take injection the way a solid wall does: the resin would just fill the hollow cores or the gaps behind the stones. For those walls, failed mortar joints are raked out and repointed, and a block wall that leaks along its base is usually better handled by draining it into interior drain tile than by trying to seal every joint.

After the crack is sealed

Look at the spot during the next few heavy rains. A dry face means the repair held. A new damp line beside it can mean a second crack the first one was masking, which happens. Mark the ends of any hairline cracks with a pencil and a date; if one grows past the mark, that is worth a call to an engineer. If water appears somewhere else entirely, start with tracing the leak.

Cracks that only leak when the river is up

Some cracks stay dry for years and then run during a long high-water stretch, when groundwater sits against the wall for days. That pattern still points to a leak rather than movement, and it is a good sign injection will work. Bring photos from the wet days to the visit if you have them.