Foundation problems
Leaking Foundation Cracks
Water is coming through a crack in my foundation. How do I stop it?
A crack leaks because water is standing against the outside of the wall with somewhere to go. The crack is the path, not the reason. Sealing it by injecting polyurethane from inside is a routine repair that works while the crack is wet and usually takes a few hours. But if the water arriving at the wall is not dealt with, it will find the next available path, which is why grading and downspouts get checked as part of the same job.
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This one splits both ways. The specifics below decide it.
What you are probably seeing
- A wet trail on the wall that leads back up to a crack
- Water appearing during or shortly after melt or heavy rain, then stopping
- White chalky deposits marking where water has evaporated over time
- Damp or discoloured drywall or flooring against the wall in a finished basement
- A musty smell in the affected corner
What causes it
- Surface water reaching the wall
- Ground sloping toward the house, a downspout discharging at the foundation, or a settled patio delivering water directly to the backfill. The most common cause and the cheapest to fix.
- Hydrostatic pressure
- Saturated soil around the foundation puts water under pressure, which then pushes through any available path rather than merely seeping.
- Failed or absent weeping tile
- The perforated pipe at the footing is meant to collect groundwater and take it away. When it silts up, collapses or was never installed, water stays against the wall.
- A window well without working drainage
- A well that fills with water is a reservoir held against the wall, and it will find the nearest crack.
- Freeze-thaw widening the path
- Water in a crack freezes and expands, opening the crack slightly each winter. This does not start the leak but tends to make it worse year over year.
How serious is yours?
The left column is worth acting on. The right column is genuinely fine to watch, and saying so is the point of this page.
Get this assessed
- Get this looked at: Water entering fast enough to accumulate on the floor
- Get this looked at: Water near electrical equipment or a furnace
- Get this looked at: The crack is horizontal as well as leaking
- Get this looked at: The crack has widened since the leak started
- Get this looked at: Water entering at several points along the wall rather than one
Reasonable to monitor
- A brief damp patch during spring melt that dries out on its own
- Slight seepage in an unfinished basement with nothing at risk
- Efflorescence with no currently active water
How it is usually dealt with
Check outside first
Downspout position, grading against the wall, window well drainage. This costs almost nothing and is frequently the entire fix, particularly for leaks that only appear during melt.
Polyurethane injection
The standard repair for a leaking crack. The resin expands on contact with water, fills the crack through the wall thickness, and stays flexible so it tolerates seasonal movement.
Exterior excavation
Where interior repair has failed, where several cracks leak, or where the weeping tile needs replacing. Addresses the water before it reaches the wall, at considerably higher cost.
Interior drainage system
Where water arrives along the joint between floor and wall rather than through one crack, the mechanism is different and a collection system is the appropriate response.
The Calgary angle
The classic Calgary version of this problem is a crack that has been dry since October and starts weeping in March. Snowmelt releases a winter of precipitation over a few warm days onto ground that is often still frozen beneath the surface and cannot take it, so water runs across the top and collects wherever it can. A leak that tracks the melt is a drainage story, and treating it as a wall problem means paying to seal a wall while the water supply stays exactly as it was.
What to do next
These cost nothing and make any later assessment considerably more useful.
- Photograph the leak while it is active, which is the most useful evidence anyone assessing it can have
- Follow the wet trail upward to find the actual entry point
- Go outside and look at grading, downspouts and window wells at that location
- Extend or redirect any downspout discharging near the wall
- Note whether the leak tracks melt, rainfall, or neither, and mention that when you request an assessment
The repair page for this problem
If you have decided it needs attention, this is the page covering what the work involves and what it costs.
Basement leak repairQuestions people actually ask
Can a leaking foundation crack be repaired from the inside?
Usually yes. Polyurethane injection fills the crack through the full thickness of the wall and is done from inside without excavation, and it works on a crack that is currently wet. What it does not do is change the water situation outside, so where the underlying cause is drainage, an interior repair addresses the symptom and the drainage still needs correcting.
Will the crack leak again after it is sealed?
A properly injected crack should not leak again at that crack. Water still arriving at the wall, though, will look for the next path, which may be another crack, a form tie hole or the floor-wall joint. That is the reason a repair that ignores drainage often feels like it moved the leak rather than fixing it.
Do I need to wait for the crack to dry before repairing it?
Not for polyurethane injection, which is designed for wet conditions and expands on contact with water. Epoxy is a different matter and generally needs a dry, stable crack, which is one of the reasons polyurethane is so commonly specified for leaking cracks in Calgary.
Is a leaking crack a structural problem?
Not by itself. Water passing through a narrow vertical crack is a water problem. It becomes a structural question when the crack is horizontal, when the two faces have moved out of line, or when the crack is widening, because those indicate the wall is moving rather than simply being permeable.
Not sure what you are looking at?
Send a description and a postal code. It goes to an independent Calgary foundation contractor who can tell you what it is.
We are a referral service, not a contractor. Your request goes to an independent Calgary foundation company.