Can I waterproof a foundation that has active water leaking through cracks right now?

Yes, you can waterproof a foundation with active water leaks, but the approach must address the active flow first before any permanent waterproofing system is installed. Trying to apply coatings or membranes directly over actively leaking cracks is a waste of money — water pressure will push through or behind any surface-applied product. The key is a staged approach: stop the active leak, then waterproof properly.

For poured concrete foundations — which are common across Scarborough, North York, Mississauga, and most post-1960s GTA homes — active crack leaks are typically handled with polyurethane crack injection. A contractor injects fast-setting polyurethane foam directly into the crack from the interior side. The foam reacts with the water, expands to fill the full depth of the crack, and cures even in wet conditions. This is specifically designed for active leaks and costs $300–$800 per crack in the GTA depending on length and accessibility. For cracks that are weeping rather than flowing, epoxy injection is another option at similar pricing, though epoxy requires a relatively dry crack face to bond properly.

If the leak is coming through mortar joints in a concrete block or brick foundation — common in pre-1975 Toronto homes — injection alone won't solve it because block walls have hollow cores and multiple pathways for water. In these cases, the long-term solution is exterior waterproofing, which means excavating down to the footing, cleaning the wall, applying a liquid rubber waterproofing membrane, installing dimpled drainage board, and replacing the weeping tile. This is the gold-standard fix and costs $3,000–$12,000 depending on the linear footage, depth of excavation, and soil conditions. GTA clay soils make excavation more labour-intensive and expensive compared to sandy soil areas.

Before any waterproofing work, check the basics first. A surprising number of active foundation leaks in the GTA are caused by simple drainage failures that can be corrected without major waterproofing. Make sure your grading slopes away from the foundation at a minimum of 6 inches over the first 6 feet. Ensure all downspouts extend at least 6 feet from the foundation wall. Check that window wells have proper covers and drains. Clearing a clogged downspout or re-grading a flower bed sometimes stops a leak entirely.

The Ontario Building Code (OBC Section 9.13.2) requires below-grade foundation walls to have dampproofing or waterproofing on the exterior surface, and Section 9.14 requires functional weeping tile around the foundation perimeter. If your home was built before these standards were enforced, or if the original dampproofing has deteriorated after decades in GTA clay soil, exterior waterproofing during a renovation is the time to bring the foundation up to current code standards.

Timing matters for exterior waterproofing in the GTA. Excavation and membrane application require dry conditions and temperatures consistently above 5°C. The practical window is mid-April through mid-November most years. Interior crack injection, however, can be done year-round since it is performed from inside the basement. If you have an active leak right now during winter or early spring, interior injection can stop the immediate problem while you plan and budget for exterior waterproofing in the warmer months. Any contractor you hire must carry valid WSIB coverage — always request a clearance certificate before work begins, as homeowners can be held liable for workplace injuries if the contractor is uninsured. Need help finding a waterproofing or parging contractor? Toronto Parging can match you with local professionals through the Toronto Construction Network for a free estimate.