How can I protect my home from water infiltration and flooding?

Millions of homeowners across Canada have basements that are prone to water infiltration. And those without basements often have crawl spaces or on-grade concrete slabs that still need protection from the seasonal flooding of snowmelt and sudden downpours. Protection from groundwater, rainwater and snowmelt seepage into building facades is crucial to guard against home flooding.

As we’ve noted previously, homeowners need to take into account the increasingly frequent and powerful precipitation events seen recently (and projected by climate scientists to continue for the foreseeable future) that can put even the most resilient waterproofing systems to the test. Keeping the water from seeping into the building envelope can be a challenge, even when basement sump pumps are installed to mitigate sewer backup.

The situation has even gotten the attention of municipal politicians, who in some low-lying areas of Montreal, Quebec, passed regulations in 2024 to ban homeowners from turning basements into habitable spaces. (Others were seeking to ban the construction of basement apartments outright!)^[1] Only weeks later, Montreal was deluged with a record 6" (152 mm) of rainfall in a single day – an amount 61% higher than the previous one-day record of 3.7" (93.5 mm) – which caused widescale flooding amounting to the costliest severe weather event in the province’s history.^[2]

How can I protect my home from flooding: Waterproofing the concrete foundation

Basements (and concrete foundations in general) are common to most single-unit dwellings built in the last hundred years or so, when concrete became the preferred choice, based on its ease of application, low cost – plus its high compressive strength and durability. However, every homeowner should know there are two types of concrete: concrete that has existing cracks and concrete that will crack (because all concrete develops some cracks). As well, concrete is a porous material. Concrete used for residential foundations tends to have a higher porosity; even more so for older houses. The presence of cracks and pores in the concrete allows for vapor and water transmission into the foundation, and ultimately the living space, resulting in either water infiltration or higher relative humidity. So preventative measures against pooling are always a good place to start.

One way to prevent excess pooling of rainwater and snowmelt is to ensure proper drainage and grading of the land around the foundation. By installing gutters with drainpipes that direct the roof water away, you can reduce the amount of water accumulating on and around the building envelope. Of course, that only works with regular inspection and maintenance to clean out any leaves and debris.

And if you are able to, maintain a graded slope downward from the building’s foundations on all sides. If your foundation sits at the bottom of a slope on one side however, drainage around the building can be difficult to achieve, and any exterior wall facing either level terrain or an upward slope will need extra protection to keep water from penetrating the basement walls or on-grade slab. And any cracks or deficiencies in the above-grade exterior facades can also be channels for unwanted water infiltration.

But not to worry: MAPEI brings over 85 years of know-how in products and system solutions for homeowners, including concrete repair and waterproofing systems. Our extensive network of international R&D laboratories has led to innovations in construction technologies like our Corrosion Inhibitor Enhanced repair mortars. These products feature proprietary additives that fortify the passivation layer on embedded reinforcing steel, enhancing its resistance to corrosion. As well, since 2023, MAPEI offers several premium products that are fully offset for CO₂ emissions throughout their entire product lifecycle, always keeping sustainability and quality top of mind.

How can I protect my home from flooding: Positive-side waterproofing of concrete foundations

For serious waterproofing protection of basement foundations, professional installers are needed. And for such jobs, MAPEI Canada offers a positive-side waterproofing system that is installed on the outboard side of the structure to keep water out of the building. The Planiseal^® Membrane SA system, based on a self-adhered waterproofing membrane, is a simple and effective means of accomplishing this goal. It prevents water intrusion into buildings following the construction of their foundation walls.

This is the product build (from the outer concrete wall):

1.  Mapebond ^™ 700 , a quick-drying, solvent-based, high-tack contact adhesive that is specifically formulated to promote maximum adhesion of MAPEI waterproofing membranes.
2. Mapeflex^® P2 NS, a two-component, nonsag, polyurethane sealant that meets the requirements of ASTM C920 for filling joints and cracks.
3. Planiseal Membrane SA, a 63-mil, self-adhering sheet membrane consisting of 61 mils of rubberized asphalt laminated to a 2-mil PET film. The combination of these two excellent waterproofing materials provides a durable, high-performance waterproofing membrane.
4. Mapedrain^™ 25, a high-strength, three-dimensional drainage composite consisting of a nonwoven filter fabric bonded to individual dimples of the molded polypropylene core, minimizing fabric intrusion into the drainage channels caused by overburden pressure.
5. Mapedrain TD Drainage Composite, a similarly designed drainage composite used in place of a conventional gravel-covered pipe drain.
6. Mapedrain TD Fittings, a variety of polyethylene components consisting of end outlet, side outlet, splice and corner fittings.

Other systems can include waterproofing coatings applied by trowel or brush. The freeze/thaw resistant Planiseal 88 can be applied on exterior concrete to a depth of 10 feet (3.05 m). This single-component, polymer-modified cementitious coating protects surfaces exposed to negative as well as positive hydrostatic pressures. Every home and environment has its own unique factors that point to using one system solution or another. Check with MAPEI’s Technical Services Department for more in-depth guidance during the planning phase.

How can I protect my home from flooding: what if I have cracks or gaps in my concrete foundation?

If the concrete foundation is exhibiting structural cracks, (i.e. cracks that are wide and keep opening up over time) then these should be evaluated by a structural engineer. In that case, MAPEI offers a variety of epoxy injection resins (such as Epojet^™ [NA]) for structural retrofit of cracks. If the design or the load capacity of the concrete is inadequate, MAPEI also offers Fiber Reinforced Polymers (FRP) systems for concrete retrofitting. 

If expansion gels or grouts are specified, MAPEI has that covered also. Resfoam^® HB 45 is a low-viscosity, flexible, hydrophobic polyurethane grout which may be used together with Resfoam HBA 45 accelerator to adjust the reaction profile for a specific application. It can expand up to 750% of its liquid volume, thus preventing water infiltration in cracks of 0.3 mm and larger. The cured Resfoam HB 45 will provide a flexible foam that can tolerate minimal movement in the cracks.

And if repair mortars are required to fill larger gaps, we have a whole suite of Concrete Repair Mortar Solutions to meet the needs of your specific job, including two that come fully offset for CO₂ emissions throughout their entire product lifecycle: Planitop^® XS fast-setting vertical and overhead repair mortar, and Mapecem^® Quickpatch high-performance concrete patch.

How can I protect my home from flooding: Waterproofing the joints

Single-family dwellings, like all buildings, are designed to be exposed to various movements, which can be caused by wind, thermal contraction between the building’s various components, stress caused by soil movement, etc. That’s why building facades require special waterproofing sealants that can follow movement in joints. This can be anywhere outer fittings connect to the main structure, or around doorframes, windows, etc.

The two most common types of waterproofing sealant technology are polyurethane and silicone. MAPEI offers easy-to-apply, gun-grade products in both categories. While the former may be cheaper, there are longer-term cost-savings to be had from protecting your home from flooding with a silicone sealant that allows for movement.

With that in mind, MAPEI Canada recently introduced a new silicone waterproofing sealant specifically for building facades in cold-weather climates: Mapesil^® F50 with elongation up to 50%. It is a UV-resistant, neutral-cure silicone sealant that can be applied at temperatures as low as -25°C on clean metals, glass, ceramic, most types of wood, and other difficult-to-bond-to substrates, such as masonry, concrete and painted surfaces. It is also available in five standard colors, or may be tinted to specific colors on demand.

If you prefer to go the polyurethane route, Mapeflex P1 FT is a nonsag, one-component, elastomeric polyurethane sealant that can accommodate joint movement as well, up to 35% (and it is paintable if that is a consideration).

How can I protect my home from flooding: Waterproofing exterior concrete balconies and decks

Another recent innovation from MAPEI is the Mapecoat^™ P 288 System, a high-build, textured, waterproof acrylic deck coating for concrete walkways, decks and balconies. This is a slightly flexible system featuring Planiseal 288, a polymer-modified cementitious waterproofing coating, reinforced with Fiberglass Mesh, and finally a durable-wear acrylic topcoat, Mapecoat Deck T. This system can be used on indoor/outdoor concrete slabs exposed to pedestrian traffic, including balconies and walkways. The easily installed Mapecoat P 288 System is available in a wide range of colors, and is designed to improve the durability of the concrete by limiting the penetration of water and chlorides; all while providing a fine, aesthetic finish to the concrete floor.

To find out more about how you can protect your home from flooding, visit our Website, www.mapei.com. There, you can find the Technical Data Sheets (TDSs) for whichever products you plan to use. And if you have questions at any point, know that the MAPEI Technical Services team is always at the ready to answer your questions and help guide you through the process every step of the way, at 1-800-361-9309.