Foundation Waterproofing Vs Foundation Dampproofing

December 3, 2012

Most people who build a new home with a basement plan on making it an added living space. New homeowners want to install a large screen TV, a pool table or maybe another bedroom. They expect that their basement will be dry and free of water. But what they don't know is that it may be possible that their basements are not waterproof.

Water vapor that gets into a basement causes the musty odors that you smell in a basement. Any liquid water that gets into a basement can damage carpets, drywall and any insulation that is installed inside the basement. And it can cause mold to grow.

First the Basics

Not all foundation coatings are waterproofing. When foundations are built, many are coated with what is called dampproofing. This is a bituminous asphalt membrane that is black in appearance. While it has been used for decades, it does not truly waterproof a basement. Dampproofing can stop water vapor, but that is it. Dampproofing cannot stop liquid water from getting through the foundation walls and into the basement.

Foundation Waterproofing Membranes

According to the ICC-ES, a non-profit public benefit corporation that evaluates products and sets performance criteria for the residential building market, waterproofing must do three things. First, it must stop water vapor. This gaseous form of water is released by the surrounding soils and can move through the foundation walls and into the basement.

Secondly, waterproofing membranes must be able to stop liquid water under hydrostatic pressure. In easy to understand terms, hydrostatic pressure is the force exerted by liquid water that is in the soil. You can think of it just like the water in a water tower. The taller the soil and therefore the higher the water column in it, the greater the hydrostatic pressure against your foundation. Also, the amount of water that is in the soil itself can affect the amount of hydrostatic pressure. The greater the amount of water in the ground, the higher the hydrostatic pressure exerted against the foundation.

Third and most important is that waterproofing must span a crack in a foundation. Foundations crack as a normal process of concrete curing, and if that crack is not sealed against water intrusion, it can leak when it rains.

Why Dampproofing will not Stop Water

Dampproofing does not have the ability to stop liquid water under hydrostatic pressure. This is because it goes on very thin, only 10 mils thick in some cases. Water under hydrostatic pressure can go right through it.

Because the dampproofing is brittle and has no flexibility, it cannot span a crack in a foundation. When the foundation cracks, so does the dampproofing. Therefore, liquid water can penetrate into the basement area.

The terms waterproofing and dampproofing are incorrectly used interchangeably. So, when you are building your new home, be sure that your builder is using a quality waterproofing membrane. It will give years of protection and effectively give you a larger living space that will stay dry and keep your finished basement safe from water.

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