Why does my basement leak?
Your basement leaks because soil outside is holding water against the wall, and the wall is giving that water a path in.
One cubic metre of water weighs a tonne. Now picture the soil against a 2.4 metre foundation wall after three days of rain, holding that weight and pressing sideways. Builders call it hydrostatic pressure. Concrete is not waterproof, and block is worse. Water only needs a cold joint, a shrinkage crack, a tie hole or a mortar bed to move through.
Much of the older housing stock around here sits in clay. Clay does not drain. It holds water, swells when wet, shrinks when dry, and moves the ground around your footings a little every season. Add freeze and thaw and you have a foundation that gets worked on by the weather every year.
The water almost always had help. A downspout dumping beside the wall. Grade sloping back toward the house. A window well with no drain in the bottom of it. A weeping tile installed in 1978 that is now full of silt and roots.
What does the white powder on my basement wall mean?
That white chalky bloom is efflorescence. It means water has passed through the concrete or block, dissolved salts on its way, and left them behind on the surface when it evaporated. It is evidence of moisture movement, not damage on its own.
Efflorescence tells you something useful. Water has been moving through that assembly, and may still be, even if you have never seen a puddle. Wipe it off and it comes back after the next wet week. Homeowners often paint over it with a sealer from the hardware store. The sealer holds until pressure builds behind it, then it blisters and peels, and you have learned nothing except that the wall is wet.
Is a hairline crack in my foundation serious?
Most hairline vertical cracks in a poured foundation are shrinkage cracks from curing, and they are common in otherwise sound walls. They become a problem when they leak or when they move. The pattern matters far more than the existence of a crack.
What we look at:
- Vertical or near vertical, hairline, no offset. Usually shrinkage. Treat it if it leaks.
- Diagonal cracks running from the corners of windows or beam pockets. Settlement. Worth a closer look.
- Stair-step cracking through the mortar joints of a block wall. The wall is moving.
- A horizontal crack partway up the wall, especially with bowing. That is lateral soil pressure, and it needs a structural engineer, not a caulking gun.
- Any crack where one side sits proud of the other. Movement, not shrinkage.
For a hairline crack, take a photo with a coin next to it and date it, then another in six months. If it grew, you have a moving crack and a different conversation. A horizontal crack, a bowing wall or an offset does not wait six months.
Should I waterproof my basement from the inside or the outside?
Exterior work stops water before it touches the wall. Interior work manages water that has already arrived. If you want the repair that lasts, and the house allows it, go outside.
A proper exterior repair is a real excavation. We dig to the footing, strip the wall back to bare concrete, repair cracks from the outside where the pressure is, then build the assembly back in order. Waterproofing membrane, not damp-proofing spray. Dimple board over it so any water that gets past has somewhere to go. New weeping tile bedded in clear stone, wrapped in filter cloth so it does not silt up in ten years. Backfill in lifts. Grade rebuilt so it sheds away from the house.
That version lasts for the life of the house. It also costs more, disturbs your landscaping, and cannot always be done.
Interior is the right call in real situations, and we recommend it without apology when they apply:
- A semi or a townhouse where the wall is shared or unreachable.
- A garage, addition, deck or pool sitting over the wall you would need to dig.
- Water coming up through the slab or at the floor-to-wall joint, which usually means groundwater below the floor rather than a leaking wall.
- A house where excavation would cost more than the basement is worth to you.
Done properly, interior means breaking the perimeter of the slab, installing a drainage channel, tying it to a sump pit, running a pump with a battery backup, and putting the floor back. It works by admitting water into the assembly and taking it away, rather than keeping it out.
Neither method is always right. An exterior dig is impossible under a shared wall or a deck, and an interior system manages water rather than stopping it.
What should a waterproofing quote include?
A real quote names the wall, the depth, the products, and what gets put back. A vague quote gives you a lump sum for waterproofing the rear foundation and leaves the expensive parts undefined.
Insist on seeing all of this in writing:
- Which walls, in metres, and to what depth. To the footing, or partway.
- What happens to the existing weeping tile. Replaced, or left in place.
- The membrane by manufacturer and product name, not the word waterproofing.
- Whether a dimple board and filter cloth are included.
- Backfill material and how it gets compacted.
- Restoration. Deck, walkway, fence, sod, interior floor. Who puts it back and to what standard.
- Sump pump, discharge location, and backup power if a pump is involved.
- The warranty, its length, what it covers, and who honours it.
The last one separates the trades. A warranty from a company that has been at the same address for years and carries proper insurance means something. A warranty on a business card does not.
What if the foundation is not the problem?
Check the cheap causes before you dig. Downspouts discharging within a metre of the wall, grade that has settled back toward the house over twenty years, a window well with no drain, a failed sump, or a cracked drain lateral in the yard. We have fixed leaking basements with a shovel, three metres of downspout extension and a Saturday afternoon, and we say so when that is the answer.
Send us photos of the wall, the crack with something for scale, and the exterior grade at that corner. Tell us what the wall does within two hours of a hard rain. We will tell you what the photographs suggest, and whether it is worth a visit. Start a conversation.