Foundation crack repair for leaks, not structure
Middlesex Waterproofing seals leaking foundation cracks from the inside, by injection in poured walls.
This page is about water, not structure. A thin crack that weeps after rain can usually be sealed from the inside. A crack that is moving, widening or pushing the wall inward is a different question, and we will tell you so.
Which cracks we inject
Poured concrete shrinks as it cures, and most foundations end up with a few hairline cracks that run up and down or on a slight angle. On their own they are not a problem. When one of them carries water through the wall, it needs sealing.
Injection fills the crack through the full thickness of the wall, so water meets resin all the way through instead of a surface patch that pops off. We clean the crack, set ports along it, seal the face and pump resin in from the bottom port up until it shows at the next one.
Good candidates
- Wall
- Poured concrete
- Direction
- Vertical or slightly diagonal
- Width
- Hairline to narrow, same width end to end
- Symptom
- Damp line, drip or white mineral trail after rain
Polyurethane or epoxy, and why it matters for a leak
Two resins are used for crack injection. Polyurethane reacts with water and expands into a flexible foam that fills the crack and stays tight if the concrete shifts a little with the seasons. That flexibility is why it is the usual choice when the goal is to stop a leak.
Epoxy cures hard and bonds the two sides of the crack together. It is used when someone wants the crack glued, which is a structural question and starts with an engineer, not with us.
The two resins
- Polyurethane
- Expands, stays flexible, seals against water
- Epoxy
- Cures rigid, bonds the crack faces
- Both
- Injected through ports from the inside
Block foundations leak differently
Injection works in solid concrete. A concrete block wall is hollow, and resin pumped into a crack in a block just disappears into the core behind it. Water in a block wall also travels: it can enter high on one side and come out low on another.
For a block wall we seal open mortar joints where they are clearly the entry point. When the wall leaks along its length, the lasting fix is to drain the cores into interior drain tile at the footing, so the water has somewhere to go besides your floor.
When a crack is a structural question
Some cracks mean the wall is moving. A horizontal crack along a block or poured wall, a wall that bows or leans inward, a stair-step crack climbing through block joints, or a crack that is wider at one end and keeps growing: these are signs of pressure or settlement, not just a leak.
When we see any of those, we stop and recommend a structural engineer. Sealing a moving crack hides the evidence without fixing the cause. We work from the inside and we do not do structural foundation repair or exterior excavation. Once an engineer has looked and the wall is stable, we are glad to come back for the water.
Signs we refer to an engineer
- Horizontal crack
- Runs along the wall, often at mid-height
- Bowing
- The wall leans or bulges into the room
- Stair-step
- Climbs diagonally through block mortar joints
- Widening
- Wider at one end, or growing over time
Older foundations around the bay and the river
Older walls have had more years to crack. In South Amboy, census estimates put close to four in ten homes at 1939 or earlier. In South River, about three quarters of homes predate 1980, and the river itself marks the borough's eastern edge. In Woodbridge, the National Weather Service lists Woodbridge Creek among the places where tidal flooding begins.