Water infiltration into your basement through the floor can be a serious problem causing significant damage to your home. Waterproofing basement floor is the best way to prevent problems. Ideally, this would be done during construction, but often is not. If you need to waterproof basement floor after the home is built, first, you must understand how and why water gets past your basement floor into your basement. Water can enter your basement by coming through:

• Cracks in the floor due to hydrostatic pressure
• Floor/Wall joint due to hydrostatic pressure
• Capillary action
• Vapour transmission due to differential
• Condensation due to a cold floor and warm, humid air in the loving space.

Waterproofing Basment Floor

Water Flooding Basement through the basement floor

Hydrostatic pressure is a technical term for water pressure. Simply put, the force of gravity exerted on a liquid at equilibrium; the weight of water bearing on an object. This happens when you have a high water table and insufficient drainage around the bottom of your foundation. The water table on the outside of the foundation will rise higher than the basement floor level causing the water trapped beneath the floor to come under pressure. As pressure builds, water will force its way into your basement through cracks in the floor and the floor/wall joint.

Capillary action is when water is “drawn” upward, against the pull of gravity through narrow tubes in porous materials called “capillaries”. Your concrete basement floor is porous and if the water table rises to come into contact with the underside of the slab, water will migrate through the floor slab due to capillary action causing a wet floor.

Vapour Transmission occurs when moisture migrates from areas of high humidity to areas of lower humidity. The soil beneath and around your foundation is at 100% humidity and as we learned above, the concrete in your home is porous and when you combine that with basement humidity between 50-65%, moisture will naturally move from the soil through the concrete into the living space without a vapour barrier.

Condensation often occurs in the summer in un-insulated basement floors. At a soil depth of 2.45m (8ft), the soil is 10˚C (53˚F) even in the summer! This cold soil keeps an un-insulated concrete floor cold. You’ve probably noticed this walking around on our bare feet. When hot, humid summer air comes into contact with the cold floor, it condenses leaving water behind like water on the outside of a glass of ice water on a hot summer day.

There are numerous ways to correct these problems and prevent them in the first place. Over the past 40+/- years an asphalt based coating has typically been applied to the outside of foundation walls as a damp proofing material to prevent vapour transmission through the walls. Spray applied damp proofing is not practical to use on a basement floor so instead, polyethylene sheeting is often installed on the sub-soils beneath the basement floor has been used over the past 30 + years as a vapour barrier to eliminate vapour transmission through the floor and minimize capillary action. Perimeter drains or footing drains as they’re sometimes called drain water away from the bottom of your foundation, lowering the water table minimizing capillary action. Over the past 25-30 years, new homes have had to have air exchangers installed which remove heavy, moist air from the basement and exhaust it to the outdoors helping to reduce condensation on the floor. To further help reduce condensation, extruded polystyrene (Styrofoam) insulation is installed beneath the concrete floor to act as a thermal break in order to help keep the floor temperature closer to room temperature, further reducing condensation.

Waterproofing basement floor is an important to the livability and enjoyment of your home. If you are considering waterproofing your basement floor, you should contact a professional to come to your home to provide a consultation and come up with a plan that’s specific to your home.


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