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Don’t Seal the Gap Between Basement Wall and Floor to Keep Out Water

Sep 30, 2015 • By Matthew Stock.

Why Does my Basement Leak Between the Wall and Floor?

One of the most common places to find water in a residential basement is in a puddle right next to the wall.

This doesn’t happen because the wall itself is leaking water or because the basement floor has low points around the edges.  It occurs with frequency because of a necessary quirk in construction that creates an avenue for water to enter the basement between the wall and floor.

Combine this with a tendency for ground water to create underground pressure and the result is a problem called cove seepage.  There is a simple solution for cove seepage but it may not be the one most people will think of first.

Why Sealing the Gap between Wall and Floor Won’t Keep Out Water

When a house is built, the construction begins with the foundation.

After the excavation is made to the depth of the basement, the foundation footings are built of poured concrete.  The footings are wide slabs that describe the perimeter of the foundation and create a base for the foundation walls.  They also help to distribute the weight of the foundation and the house to prevent settling and sinking.

The footings are typically designed with a narrow channel molded into the top that is called the “keyway.”

Once the footings have cured, forms are built on top and the walls are poured.  The bottom edge of the wall conforms to the keyway, creating a “tab and slot” configuration that helps keep the wall and footing aligned.  Even so, the new concrete does not bond with the already-cured footings so a tiny gap exists between the two.

After the walls have cured, the basement floor is poured, leaving a similar tiny gap, known as the “cove joint,” between the cured walls and newly poured floor.

Under ordinary circumstances, this gap is too small to admit water.  However, when heavy rains or other occurrences cause the water table to rise, hydrostatic pressure under the basement floor increases and pushes the water through the cove joint.  If the basement floor has cracks, these will also leak water when hydrostatic pressure increases.

When this occurs, whether the homeowner understands the physics behind it or not, his or her first impulse is often to plug the gap between floor and wall, typically using hydraulic cement or some other “waterproof” sealant.

To put it bluntly, this just doesn’t work.  Consider this:  If the water pressure outside the foundation is strong enough to force a significant amount of water through a gap barely visible to the naked eye, what will it do a sealant applied from the inside?  One of two things – either force the water around it or cause it to pop out.  In either event, the sealant has failed.

So, what’s the answer to seepage between wall and floor?  Drain tile.  Drain tile is a sub-surface drain placed below the basement floor that alleviates hydrostatic pressure and carries away the ground water that causes it.  Consisting of perforated flexible plastic pipe buried in a bed of washed gravel, interior drain tile (placed on the inside perimeter of the footings) connects to a sump pit so that water that would otherwise end up on the basement floor is discharged from the basement by a sump pump.

Of course, installing interior drain tile is not a DIY project; it requires the expertise and services of an experienced basement waterproofing contractor.  At U.S. Waterproofing, we have kept basements dry for thousands of customers by installing interior drain tile since our founding in 1957 and we continue to implement the latest materials and techniques.  Why not ask for our free advice?  If an in-person appointment is inconvenient, try our exclusive Virtual Advisor.

If you’d like to know more about the right way to stop water coming through the gap between your basement wall and floor, please post your questions in the Comments box below.

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