Basement Wall Waterproofing: What to Do and What to Avoid

Basements, being situated below ground level, often contend with moisture issues. This can manifest as occasional dampness on basement walls, scattered water puddles, or, in more severe cases, flooding during rainy periods.

A consistently humid or wet basement can lead to problems such as paint peeling, the growth of mould and mildew, deterioration of wood and concrete structures.

Builders typically implement waterproofing measures during the initial construction of basements. However, as a house or building settles over time, it can develop cracks in its basement walls. These cracks, especially when the soil outside becomes saturated, can allow water to infiltrate.

DO: Identify the Source of Water Before Waterproofing Basement Walls

The initial step in waterproofing basement walls is to determine the source of the water infiltration. Concrete walls are porous, which often results in visible wet streaks that indicate where water is entering.

Look for these streaks along cracks, in the corners of windows, between mortar joints (for cement block walls), and around areas where pipes enter or exit, like water-supply lines or sewer pipes.

DON’T: Attempt Wall Repairs with Standing Water in the Basement

In rainy seasons, a crack in a basement wall may allow water to enter. Before you address the crack, it’s crucial to remove all standing water from the basement. Working in a flooded basement significantly increases the risk of electrical shock or electrocution.

Start by turning off the power to the basement, and then use a utility pump, connected to an extension cord that reaches an upstairs outlet, to remove the water. The pump will discharge the water onto the surface of your yard through a garden hose. Once the basement is free of water, you can proceed with inspecting, repairing, and effectively waterproofing the basement walls.

DO: Fill Cracks with Hydraulic Cement

In many instances, cracks tend to appear at the base of basement walls. During the foundation construction process, the footing—a wide, flat base constructed from concrete and reinforced steel, designed to support the walls—is poured first.

Subsequently, the walls are poured on top once the footings have hardened. While this follows standard construction procedures, it can lead to what’s known as a “cold joint.” This creates a vulnerable point in the foundation between the wall and the footing where cracks can develop due to the shifting and settling of the foundation, as well as the lateral pressure from the soil.

Hydraulic cement, which incorporates additives that cause it to expand and set quickly, is mixed with water to create a dense putty-like consistency.

This mixture is then pressed into the cracks using gloved fingers or a putty knife (be sure to follow the mixing and application instructions on the product’s packaging). As hydraulic cement expands, it penetrates deep into the cracks and crevices, forming a watertight seal.

However, it’s crucial to mix only as much as you can use within 3 minutes, as that’s how quickly it starts to set.

DON’T: Overlook Window Well Leaks

Window wells often serve as a common source of leaks in basement walls, particularly if a proper drainage system was not installed beneath the well during the home’s construction.

This can result in water accumulating around the bottom of a basement window and eventually seeping inside.

Do take proactive measures to protect your basement from water-related issues

Regularly inspect and, if necessary, repair your gutters and downspouts to ensure they divert water away from your home. Additionally, it’s advisable to slope your yard away from the foundation with at least a 2 percent incline.

Consider the installation of an exterior drain tile system as a more drastic measure. While it can be costly, it involves excavating the soil around your basement’s exterior to place a perforated drain at the footing level.

Often, a waterproof membrane is added to the outer basement wall, and a buried sump pump is installed to collect and pump away water. This complex task should be undertaken by a professional foundation contractor and has the potential to significantly reduce basement water issues.

For more information, news and tips around building waterproofing, visit the MJ Engineering website.