leaking basement Toronto where basement floor meets wall

Water leaking through top of foundation wall

As a waterproofing contractor here in Toronto, I’m often asked what is the most common cause of a leaking basement. But first, I want you to conduct a small experiment for me.

Take a used tin can (baked beans, peas, whatever) and remove the bottom end. Then, place the open-ended can in a cooking pot that’s a little taller than it. Hold it down as you slowly fill the pot with water to just below the top end of the can. While you watch:

  • Water seeps into the can past the bottom end
  • The rate increases as the outside water-level rises
  • Finally, the water levels are the same on the inside and the outside

Two things are relevant here. First, there was no seal between the bottom of the tin can and the cooking pot. Secondly, the water found a way inside the can because of what’s called hydrostatic pressure.

Basement Basics

A basement is comprised of two separate structures which are by definition underground. These are:

  • A concrete floor set in an excavated space (the “cooking pot”)
  • A rectangle of four walls standing on it  (the “tin can”)

If you were to fill the excavated space with water, this would place hydrostatic pressure on the structure. In turn, this would seek relief by entering the basement through the concrete floor and walls. These may be well waterproofed; however, as the structure settles, the joint between them weakens and gives way to water pressure.

And that, my friend, is the most common cause of leaking basements. In fact, it’s almost built into the basic design. Just like your camping tent in a storm, the leak is usually at the seam.

 

Interior weeping tile system image

Interior Weeping Tile System

How to Avoid the Problem

Do you remember how the flow of water into the tin can increase as the water level rose? The same is equally true of a leaky basement. The correct solution is installing an outside drain at floor level. This leads the underground water away as it arrives, so it never builds up enough pressure to become a problem.

In the basement water-proofing industry we call this a weeping tile or french drain system. They’re simple to install during initial construction, but a messy job to repair and install after construction. Getting a certified and insured waterproofing contractor is important if you think you may need this type of work.

Basement First-Aid

In my decades in the basement repair business, I’ve come across countless botched repair jobs involving water-proofing interior basement walls. While waterproofing your foundation can be effective if done properly, if there is an outside water source placing constant pressure on your foundation, it probably won’t last. The hydrostatic pressure invariably dislodges the material, especially since the area was inevitably damp when the seal was applied.

The only solution that’s effective is an interior water-catchment system that feeds a sump pump to an outside drainage point. It’s expensive though. However, it’s also better than abandoning a working basement, which could otherwise add good value to your home.

Is water seeping through your concrete foundation?  If left untreated, water can slowly erode your foundation and lead to costly foundation repairs.  Here in Toronto, we respond to several hundred basement waterproofing calls a year.  Some repairs are minor, while others are costly repairs.  Most of the costly foundation repairs we treat could have been prevented, or at least minimized, if proper measures had been taken earlier.

One of the foundation problems we frequently come across is a slowly eroding foundation due to a prolonged period of water penetration.

Nature often has its way with buildings, no matter the constructors’ intentions. Sometimes builders don’t try hard at all. Perhaps they are running short on time or materials. Possibly, they don’t understand the theory behind what they are doing. Property owners end up with the result, long after the construction team is gone.

In this article, we examine the phenomenon of wet concrete foundations. What causes them, why they happen in some places and not in others, what to do about the problem, and so on.

The Inherent Weakness of Concrete

Concrete consists of five essential ingredients:

  • The first is stone chip that adds bulk and strength.
  • The second is the steel bars that prevent the mix from cracking.
  • The others are cement mixed with sand to form a “glue” that holds the thing together when water’s added.

Concrete is porous when it’s dry. When there’s water in the area, it sucks it up like a giant wick.

Where Does the Water Comes From?

Dig a hole that’s deep enough, and it starts to fill with water like a drinking well. That’s because there’s always water somewhere beneath the ground. The only uncertainty is the depth. It could come from rainwater that’s filtered down, from an underground stream, from a leaking water pipe, or from a leach drain.

The same gravity that prevents us from flying off the earth presses down upon the ground, compressing it. This force pressurizes the moisture just like when a child squeezes the trigger on a toy water gun. Scientists call the energy that results hydrostatic pressure. This turns ground water into a mighty powerful thing that can find a way through most materials.

Concrete is a Natural Target

We mentioned earlier that dry concrete acts like a natural wick. As the water pooled on top evaporates, it siphons up more to replace it. This is why vacuuming it away seldom helps. Sometimes the concrete cracks due to poor construction methods, ground movement, or a weak mixture of the “glue”. When this happens, groundwater comes bubbling up through a fissure.

How to Prevent This From Happening

As we said earlier, nature will have its way. If you must build in damp earth, you can try to divert the water by installing French drains, and putting down a moisture barrier before you cast the slab. This is by no means as simple a matter as it may sound. Water is a dynamic thing and incredibly persistent.

What to Do if This Fails

Over time, the water permeating through your concrete floor is going to soften and dilute the glue, eventually causing it to begin to disintegrate. There are two strategies to counter this.

  • The preferred one is to install French drains that lead the groundwater elsewhere.
  • Second prize is to try to stop the siphon process by applying a waterproofing medium on top.

More often than not, you need a combination of the two to achieve success.