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Interior vs. Exterior Waterproofing Methods for Chicago Basements

May 13, 2013 • By Matthew Stock.

Interior vs. Exterior Waterproofing Methods for Chicago Basements


Basements are supposed to be dry so they can safely be used as storage, work or living space.  When a basement has water seepage not only is its use compromised but the resulting dampness and mold growth can affect the health of the home’s residents.  So it’s a fairly simple conclusion that when a basement experiences seepage or dampness that it’s time to waterproof.

One of the first questions a homeowner will ask is “how?” and there are several different answers depending on the source of water, construction of the foundation and other contributing factors.  The first decision to be made, however, is whether it is better to waterproof a specific basement from the interior or the exterior because there are significant differences in the methods.

Interior vs. Exterior Waterproofing Methods

Interior Waterproofing – There are two basic methods of interior waterproofing; one strictly for poured concrete foundations, the other suitable for any basement.

  • Crack Injection – The leading source of seepage in basements with poured concrete foundations, the most common in Chicago, is non-structural cracks in the walls.  These cracks can be formed by settling or sinking of the foundation or by slight inward movement of the wall due to lateral pressure from over-saturated soil outside.  The best way to repair a non-structural crack in a poured concrete wall is to inject it with expanding polyurethane.  The urethane expands to fill the crack completely, all the way to the outside soil and forms a permanent, waterproof seal that remains flexible to prevent re-cracking from minor foundation movement.
  • Interior Drain Tile – Another variety of basement seepage arises from hydrostatic pressure in the soil under the foundation, which causes water to enter the basement through the cove joint or cracks in the basement floor.  Installing drain tile inside the foundation’s footings will alleviate the pressure and carry the water off to a sump pump where it is removed from the house.  Interior drain tile, perforated pipe buried in a bed of washed stone, is maintenance-free once installed and will continue to function through the life of the home.

Exterior Waterproofing – There are also two basic methods of exterior waterproofing, one a simple approach to crack repair, the other a comprehensive system of foundation protection.

  • Crack Repair – If a non-structural crack in a poured concrete foundation wall cannot be repaired from the inside with urethane injection, it can be repaired from the exterior.  The installer digs a small-diameter hole next to the foundation at the site of the crack that extends down to the footings.  He then fills the hole with dry sodium bentonite clay, which absorbs water from the soil to become plastic then sets up as a permanent, pliable seal against further water infiltration through the crack.
Exterior waterproofing
  • Exterior Waterproofing Membrane with Drain Tile – Water can also enter a basement over the top of or through foundation walls via deteriorated mortar joints in masonry walls, through porous concrete block or brick and through honeycombed concrete.  The best way to stop this infiltration is to apply an exterior waterproofing membrane to the foundation wall, which is a thick coating of asphalt-modified polyurethane that is troweled onto the wall to create a permanent “positive-side” seal against ground water.  When exterior drain tile is installed along the outside perimeter of the footings, drainage board is added to cover the membrane and channel water down to the drain tile, which carries it off to the sump pump.

Of course, there are a number of reasons why a basement waterproofing professional will recommend interior or exterior waterproofing in a particular home and they will be covered in a subsequent article.

A Chicago homeowner with a wet basement must be confident in the recommendation of the basement waterproofing contractor he or she chooses to solve the problem.  At U.S. Waterproofing, we have been keeping Chicago basements dry for more than 55 years and, because we offer a comprehensive selection of products and services, we can recommend what’s best for your home, not just what we have available.  Why not ask for our free advice?

Tags: exterior waterproofing, interior waterproofing, interior vs. exterior waterproofing

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