- Last updated: January 20, 2026
Terry Kobatskyi
Terry is a reliable project manager with over 15 years in construction field, who has started his career of working in the trenches. More About Terry
The short answer is yes — and in many cases, winter is actually a better time to seal foundation cracks than spring or summer.
That surprises most homeowners. The assumption is that cold temperatures make waterproofing work impossible or ineffective. But the reality is more nuanced — and once you understand what’s actually happening to your foundation during an Ontario winter, the case for acting now becomes clear.
This guide covers what types of cracks can be sealed in winter, how the repair materials work in cold temperatures, when you genuinely do need to wait for warmer weather, and what happens to your foundation if you leave cracks unaddressed until spring.
Key Takeaways
- Foundation cracks can be professionally sealed year-round in Ontario — including in cold weather
- Epoxy and polyurethane injection — the professional methods used by Aquatech — both cure effectively in low temperatures when properly applied
- Exterior crack repair is the one exception: it requires excavation and is best scheduled for spring through fall
- Ontario’s freeze-thaw cycle actively widens existing cracks every winter — waiting until spring means the crack you have today is a larger crack by April
- Winter is often the best season to book — shorter wait times and the same quality results
- Foundation crack repair from Aquatech starts at $400 per crack
What's Actually Happening to Your Foundation Cracks This Winter
Before deciding whether to act now or wait, it helps to understand what Ontario winters are doing to existing cracks in your foundation.
Concrete is a porous material. Water — from soil moisture, snowmelt, and rain — seeps into cracks throughout the year. In winter, that water freezes. Water expands by approximately 9% when it freezes. Inside a foundation crack, this expansion exerts force outward against the crack walls — widening them slightly with every freeze cycle.
Then temperatures rise, the water melts, and the crack doesn’t return to exactly its previous width. It stays slightly more open than before. The next freeze widens it a little more.
This is why homeowners who notice a hairline crack in November often find a noticeably wider crack by March. The freeze-thaw cycle doesn’t pause for winter — it’s actively working on your foundation right now.
The practical implication: A crack that costs $400 to seal today may cost significantly more to repair in spring if it’s widened to the point where it requires structural intervention rather than injection alone.
Types of Foundation Cracks — Which Can Be Sealed in Winter?
Not all foundation cracks are the same, and they don’t all require the same repair method. Here’s how to understand what you’re looking at.
Vertical Cracks
What causes them: Shrinkage during the original concrete cure, or minor settlement as the foundation adjusts to soil load over time.
What they mean: Vertical cracks are the most common type in GTA poured concrete foundations. They are typically not structural concerns unless they’re very wide (more than 6mm) or show signs of differential movement. However, they are reliable water entry points and worsen with every freeze-thaw cycle.
Winter repair: ✅ Yes — vertical cracks are the most straightforward winter repair. Epoxy or polyurethane injection seals them from the inside out in a single visit.
Diagonal Cracks
What causes them: Differential settlement — one section of the foundation settling faster or more than another. Also common at the corners of window and door openings where stress concentrates.
What they mean: Minor diagonal cracks from initial settlement are common and not necessarily alarming. Actively growing diagonal cracks, or diagonal cracks accompanied by visible displacement (one side of the crack higher than the other), warrant a structural assessment.
Winter repair: ✅ Yes for stable diagonal cracks — injection seals the water entry point. ⚠ For active structural cracks showing displacement or recent growth, a professional assessment should determine whether structural repair is needed alongside or before injection.
Horizontal Cracks
What causes them: Lateral soil pressure — typically in block (CMU) foundations, where soil on the outside is pushing inward with more force than the wall can fully resist.
What they mean: Horizontal cracks are the most structurally serious type. They indicate that the foundation wall is being pushed inward and may be bowing. This is a structural issue, not just a waterproofing issue.
Winter repair: ⚠ The crack itself can be sealed in winter to stop water infiltration. However, the underlying structural cause — lateral soil pressure — needs to be assessed and addressed separately. Do not ignore horizontal cracks and treat them as a simple waterproofing issue.
Stair-Step Cracks (Block Foundations)
What causes them: Settlement, mortar joint deterioration, or water infiltration through the mortar joints in concrete block (CMU) foundations. The crack follows the weakest path — along the mortar between blocks.
What they mean: Common in older Toronto-area homes with block foundations. Can indicate settlement or ongoing water infiltration that’s deteriorating the mortar.
Winter repair: ✅ Yes — mortar joint repointing and sealant injection can be performed in winter for interior-accessible cracks.
Tie Rod Holes
What causes them: These are not cracks — they’re the holes left by the metal rods used to hold concrete formwork in place during original construction. The plugs that fill them deteriorate over time, creating water entry points.
What they mean: Very common in poured concrete foundations and a frequently missed water entry source. Not structural.
Winter repair: ✅ Yes — hydraulic cement and sealant application works in cold weather and can be completed in a single visit.
How Epoxy and Polyurethane Injection Work in Cold Weather
The two professional methods for sealing foundation cracks from the inside — epoxy injection and polyurethane injection — both work in cold temperatures, but with some important nuances.
Epoxy Injection
Epoxy is a two-component adhesive that, when injected under pressure into a crack, bonds to the concrete on both sides and restores the wall’s structural continuity. It cures to a rigid, load-bearing bond — stronger than the original concrete.
In cold weather: Epoxy cures through a chemical reaction, not evaporation. Cold temperatures slow the reaction but do not prevent it. Professional epoxy products used by Aquatech are specifically formulated for use in temperatures as low as 4°C (39°F). In practice, this covers the majority of Ontario winters when work is being performed inside a basement — the interior wall surface temperature is typically several degrees above the outdoor air temperature.
Best for: Structural cracks where load transfer across the crack is important. Vertical and diagonal cracks where the crack is stable (not actively moving).
Not ideal for: Cracks where some ongoing movement is expected, or active water-bearing cracks where water presence would dilute the epoxy before it cures.
Polyurethane Injection
Polyurethane foam is a single-component material that expands when it contacts moisture. When injected into a water-bearing crack under pressure, it reacts with the moisture present in the crack, expands to fill the void completely, and cures to a flexible, watertight seal.
In cold weather: Polyurethane injection actually works particularly well in winter conditions. The moisture present in a cold crack — including partially frozen moisture — provides the catalyst for the curing reaction. The flexible final product accommodates slight ongoing crack movement from freeze-thaw cycling without re-opening.
Best for: Actively leaking or water-bearing cracks, cracks in areas prone to minor seasonal movement, cracks where flexibility is more important than structural rigidity.
Not ideal for: Dry cracks where load transfer is the priority — epoxy is stronger for those.
The Cost of Waiting: What Happens If You Leave Cracks Until Spring
Every Ontario homeowner who has noticed a foundation crack in fall and thought “I’ll deal with it in spring” has likely found the same thing in April: the crack is worse.
Here’s the realistic progression of an unsealed foundation crack through a Toronto winter:
- November–December: Crack is narrow, injection is straightforward, cost is $400–$800
- January–March: Multiple freeze-thaw cycles expand the crack. Width increases. Water infiltration increases. By March, the crack may now require a different approach
- April–May: Spring snowmelt arrives. Water pressure against the now-wider crack increases significantly. If the crack is in a position where hydrostatic pressure builds — particularly near the floor-wall joint or at mid-wall height — active leaking begins
- Post-flood scenario: Water damage to flooring, drywall, insulation, stored belongings, or foundation structure — costs that dwarf the original crack repair
The $400–$800 repair in November becomes a $2,000–$8,000 problem by May if it includes water damage remediation alongside the now-more-complex crack repair.
Book a Consultation Now
Don’t let winter weather fool you. Small foundation cracks can turn into big problems, and the best time to fix them is when they’re discovered – regardless of the season. Aquatech Waterproofing is here to ensure your home stays dry and stable year-round. Book a consultation with us to have your foundation assessed and repaired with the utmost professionalism and care.
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Frequently Asked Questions
Yes, with important nuances. Interior crack repair — epoxy and polyurethane injection from inside the basement — is effective when the wall surface temperature is above approximately 4°C (39°F). Since interior basement wall temperatures typically remain above this threshold even during cold winters, interior repairs are performed year-round. The only genuinely temperature-limited work is exterior waterproofing requiring soil excavation.
Yes, when performed by a professional using appropriate cold-weather materials and techniques. The key variables are surface preparation, material temperature management, and using injection products formulated for low-temperature curing — all of which Aquatech’s technicians account for as standard practice.
Epoxy cures rigid and bonds structurally to both sides of the crack — it’s the right choice for stable, dry cracks where restoring structural continuity matters. Polyurethane expands on contact with moisture, fills the crack completely, and cures flexible — it’s the right choice for actively water-bearing cracks and cracks that experience minor seasonal movement. Many cracks benefit from a combination of both.
Yes. A crack that hasn’t leaked yet is still a path of least resistance for water under pressure. Spring snowmelt creates exactly the kind of sustained hydrostatic pressure that turns a previously dry crack into an active leak. Sealing it now is significantly cheaper than repairing the water damage after it leaks for the first time.
Horizontal cracks — running across the wall — are always structural concerns and require professional assessment beyond injection alone. Vertical and diagonal cracks are typically waterproofing issues when they don’t show displacement (one side higher or further in than the other) and aren’t actively growing. If you’re unsure, call Aquatech for a free assessment — we’ll tell you honestly what you’re dealing with.
Foundation crack repair at Aquatech starts at $400 per crack and typically runs $400–$1,200 depending on the crack’s length, depth, and whether structural factors are involved. We provide free, no-obligation estimates. Book yours here →
Possibly. Foundation cracks are entry points not just for water but for soil gases including radon and musty soil odour. Sealing them reduces air infiltration through the wall. However, if the smell is from mould that’s already established from previous moisture, the mould needs to be addressed separately alongside the crack repair.
DIY surface sealants — hydraulic cement, caulk, epoxy putty — fill the crack face but don’t penetrate through the full depth of the wall. When spring snowmelt creates hydrostatic pressure, water finds the unsealed portion of the crack deeper in the wall and eventually forces past the surface patch. Professional pressure injection fills the crack through its complete depth from interior face to exterior — which is why it holds permanently.
