When most homeowners have their foundation walls waterproofed, they mostly focus on the interior walls of the basement. Not only is this usually enough to keep a basement dry and a foundation stable, but modern technology makes it relatively easy to do. Interior drain tile can stop seepage from cracks in the interior wall, and the cracks themselves can be filled with expanding polyurethane for a permanent fix.

Even though waterproofing interior walls is often enough, there are still some good reasons for waterproofing exterior foundation walls as well. After all, the exterior is where the water is, so it makes sense to waterproof the outside of your foundation walls. It also protects your foundation from soil that expands when it absorbs water. The kind of clay soil that is found throughout the Midwest is particularly expansive and allows for very little drainage. As this soil expands, it puts a lot of pressure on exterior foundation walls. This is unlikely to cause too much serious damage, but it can force water through more porous spots of the walls.

How Exterior Foundation Walls are Waterproofed

The easiest way to waterproof an exterior foundation wall is to apply a layer of asphalt-modified polyurethane. When this substance dries, it creates a membrane that both keeps water out and reinforces the structural integrity of the foundation. Asphalt-modified polyurethane is sometimes mistaken for tar, but the two substances are actually very different aside from their black color. Tar simply does not have the same properties, making it a poor choice for waterproofing a foundation. Foundation walls can also be waterproofed with exterior drain tile. This is harder to install, but it is very effective in regions with a higher water table.

Whether an exterior foundation wall is coated with a membrane or tile, the foundation must first be dug up and cleaned out. This does require a lot of work, but the end result is often worth the effort if you’ve had problems with moisture in your basement in the past. Waterproofing the exterior of your foundation is always a good solution when waterproofing the inside of your basement isn’t enough to keep everything dry.