Canada has more lakes than any other country on Earth – home to an astonishing 2 million of them! All that water is a great thing… though not always. That water does unfortunately have some downsides to it as the country is more prone to flooding than most other developed countries.
Residents of Toronto learned that the hard way last summer as they grappled with two floods that combined caused over $1 billion of damage, making it the second costliest summer for flooding in the history of the province (after 2013). That same summer Quebec outdid that milestone. Residents of Montreal and elsewhere in Quebec paid a hefty price due to flooding, dealing out $2.5 billion of damage, making it the costliest severe weather event in their province’s history.
Basements take the brunt of that flooding damage. And while flooding is on people’s minds since it’s what makes the news, it’s not just flooding that basements have to deal with. Particularly in Canada, basements are subjected to extreme weather conditions: from spring thaw and heavy rainfall to deep winter freezes. These conditions make proper basement waterproofing essential – not only to maintain structural integrity but to ensure your home remains healthy, mould-free and energy efficient.
Whether you’re waterproofing a basement in Toronto, Montreal or in many other parts in the country, protecting your home from moisture intrusion is key to avoiding costly water damage. While external waterproofing is ideal, it’s often costly and invasive. Fortunately, interior basement waterproofing can be a viable and cost-effective DIY solution – especially if you’re dealing with moisture seepage rather than full-on water ingress. First we’ll discuss interior waterproofing in general, then show you how to waterproof a basement from inside. OK, let’s get to it!
Why Interior Waterproofing?
Waterproofing from the inside is typically used to manage moisture infiltration after it has penetrated the exterior wall but before it causes major damage to the interior space. It is generally less expensive and less invasive than exterior options and can be a good solution for damp or leaky basements where the water intrusion is not structural in nature.
In Canada, where cold winters and wet springs are common, basements are often built with concrete block or poured concrete foundations. Cracks in the foundation, poor grading outside and high humidity levels inside can all contribute to water seepage. Interior waterproofing helps control these issues by sealing surfaces, redirecting water and improving air quality.
Is This a DIY Job?
Get the Green Building Project Checklist
Use this handy checklist on your next project to keep track of all the ways you can make your home more energy-efficient and sustainable.
Yes – waterproofing basement walls from the inside can often be a do-it-yourself project, provided the issue is limited to minor seepage, dampness or hairline cracks. However, if you’re seeing major water leaks, bowed walls, or signs of foundation settlement, professional help is essential. Also, if you’re unsure about the source of the water, it’s worth hiring an expert to assess the problem before you begin.
What You’ll Need
Tools and equipment:
- Wire brush
- Shop vacuum
- Masonry chisel and hammer
- Caulking gun
- Paint roller or sprayer
- Putty knife or trowel
- Gloves, goggles, and respirator (for safety)
Materials:
- Hydraulic cement or crack filler
- Concrete patch compound
- Masonry waterproofing paint (elastomeric or crystalline-based)
- Waterproof caulk (polyurethane or silicone-based)
- Dehumidifier (optional but recommended)
Step-by-Step Instructions
1. Identify the Source of Moisture
Before you begin any work, determine whether the moisture is coming from condensation, seepage through cracks or water wicking through porous concrete. An easy test is to tape a square of plastic (about 12×12 inches) to the wall and leave it for 24-48 hours. If moisture forms on the wall side of the plastic, water is coming through the wall. If it forms on the room side, it’s condensation.
In colder Canadian climates, condensation can be common in basements without proper ventilation or with poor insulation. Seepage and wall absorption are more likely in spring, during snowmelt or heavy rain.
2. Prepare the Walls
Remove all paint, dirt, efflorescence (white powdery residue) and debris using a wire brush and a shop vacuum. If there is mould or mildew, clean it with a solution of water and vinegar or a mould-killing product approved for masonry surfaces. Never apply waterproofing coatings to painted walls; they must be bare for proper adhesion.
If there is old waterproofing paint, it may need to be sandblasted or removed with a chemical stripper – a tedious task but critical for success.
3. Repair Cracks and Joints
Use a chisel and hammer to slightly widen any cracks into a V-shape, which helps filler adhere better. Clean out debris and then apply hydraulic cement or a specialized concrete crack filler, pressing it deep into the crack with a putty knife or trowel. Hydraulic cement is ideal for active leaks because it expands as it cures and sets quickly, even under wet conditions.
Don’t forget the wall-floor joint (the cove joint), which is a common entry point for water. Seal it with hydraulic cement or an elastomeric sealant rated for below-grade use.
4. Apply Waterproof Coating
Once the cracks are sealed and the cement is cured (usually after 24 hours), apply a masonry waterproofing paint. There are two main types:
Elastomeric coatings – These coatings stretch and flex slightly, making them good for small foundation movement. Examples include Drylok Extreme or Sika Waterbarrier.
Crystalline-based sealers – They react with moisture in the concrete to form crystals that block water pathways. They are highly durable and often used in commercial applications. Xypex is one brand known for this type of product.
Apply the coating using a roller or sprayer. Make sure to press the paint into the pores of the wall, not just brush it on the surface. Two coats are generally recommended, applied in perpendicular directions (e.g., first coat vertically, second horizontally) for complete coverage.
These products are rated for below-grade use and designed to resist the hydrostatic pressure that can push water through concrete. Follow the manufacturer’s drying and curing times exactly.
5. Manage Humidity
Even with waterproofed walls, basements in Canada are naturally humid due to being below ground and subjected to seasonal moisture. Install a dehumidifier rated for basement use to maintain relative humidity around 40-60 percent. This helps prevent future condensation and mould growth.
Also, ensure you have proper ventilation. If the basement is finished, use moisture-resistant materials and consider a heat recovery ventilator (HRV) if the space is frequently occupied.
Optional: Install an Interior Drainage System
For homes with ongoing water intrusion or hydrostatic pressure, an interior drainage channel – also called a French drain or perimeter drain – can be installed along the basement floor near the wall. This system collects water and channels it to a sump pump.
While this is a more advanced DIY project, many homeowners can tackle it with proper planning. It involves breaking up the floor slab around the perimeter, laying drain tile in a trench, and reinstalling the slab over a gravel base. This method won’t stop water from entering, but it will safely manage and redirect it.
Considerations for Canadian Homes
Due to freeze-thaw cycles and heavy snowmelt, Canadian basements are prone to more extreme conditions than those in temperate climates. Below are a few tips useful for Canadian homes.
Insulation – If insulating the basement, never use vapour barriers on the interior side of below-grade walls without proper moisture control. They can trap water vapour and cause mould. Use vapour-permeable insulation like mineral wool and let the wall “breathe.”
Cold-climate coatings – Always check that your waterproofing product is rated for use in freezing temperatures. Some elastomeric coatings are only effective above certain temperatures and should be applied in spring or summer.
Building code – Canadian building codes (e.g., Ontario Building Code) emphasize proper moisture management for basements. If your home is undergoing renovation or resale, interior waterproofing should be done in line with these codes.
Waterproofing basement walls from the inside is a cost-effective way to control moisture, prevent mould growth and protect your home’s structural integrity, especially in the challenging climate of Canada. If your problem is more severe and you need external waterproofing done or if you don’t want to handle this job yourself, consider hiring a professional. Learn about the costs involved in our article The Average Cost of Basement Waterproofing in Canada.
