basement waterproofing

Humidity is an expression of the amount of water in the air. Humidity tends to increase during hot summer months, and is can be found indoors in any climate, especially like here on Toronto where we tend to have cold Winters and sometimes Scorching Summers with lots of rain and climate swings in between. We feel uncomfortable when the ambient humidity is high because it reduces the effectiveness of the natural cooling process we call sweating. The higher the ambient humidity level, the happier mould becomes though. And that’s a double-bind that’s best avoided at any time.

Mold in finished basement Toronto

Our basements are mini climatic systems too (although builders set out to ensure they remain as dry as deserts). That’s because the earth we build on is dynamic, and heaves and shifts naturally as its own moisture levels vary. And as it does so, it exerts massive pressure on our basement structures. The almost inescapable result is cracking, followed inevitably by water seepage.

Your Basement – A Lifelong Project

If you have a basement that’s completely watertight, then count yourself among the lucky ones. That’s because, when soil is saturated with rainwater, it’s as good as having a dam outside, thanks to force of hydrostatic pressure. Few cement-based building materials are one hundred per cent waterproof either. True foundation waterproofing uses rubber membranes on the exterior of the home. When you think about it, that’s why we build houses above the ground on foundations, and set roofs on top of them.

Finished basement with musty odour

Your Counter Measures

  1. Detect the Signs – The first thing you need to do is keep your nose tuned in to the slightest distinctive whiff of dampness, humidity or mould downstairs. When you detect something like that, it’s time to conduct a visual examination. That mould or damp spot has to be someplace, and that’s somewhere near the root cause too.


  1. Find the Spot – It’s important to remember that damp and humidity vary according to the season, and what’s happening on the far side of the basement. When it’s present on the walls it shows as a blush of water, a trickle or a dribble. On the floor, things are simpler because it forms a puddle somewhere or soaks the flooring above it.


  1. Detect the Source – If water’s dripping through the ceiling, it’s likely caused by a leaky pipe upstairs. If it appears on a wall instead, then that wall is either cracked, or the moisture is following a gap caused by an intruding pipe, or during the building process. Water on the floor is either the result of those wall or ceiling leaks, or caused by a more serious problem because you have water welling up from down below.


  1. Fix the Problem – While it is possible to seal a tiny crack from inside (although this is never a permanent solution) more serious basement damp problems require professional solutions that involve tackling the problem at its source – and that’s inevitably beyond the walls or below the floor.

We wish we could be more positive about the “instant solutions” offered on the internet and in hardware stores. At best, they conceal the problem while the hidden damage worsens. Using a dehumidifier can reduce the dampness in the basement, but it won’t fix the problem and will leave you with another daily chore of emptying the tank every day.



Vertical Foundation Wall Cracks

A foundation is the structure on which a home or other building rests. It may be a simple trench filled with concrete on which the brick walls stand. It could also be a concrete-reinforced sheet under the entire building. Where the ground slopes, there may be foundation walls as well, to make up the height difference.

Where a basement is constructed beneath a dwelling, these foundation walls go up to full room height, and receive immense pressure from the weight above them. Unfortunately not all builders make good engineers. If the forces bearing down on foundation walls are incorrectly calculated – or they are inadequately supported by their footings – then the walls will inevitably crack.  Cracks in the foundation can also be a result of shifting of the earth around the foundation, causing enough movement and stress for it to crack.

Toronto home with vertical crack in foundation

Warning Signs

Vertical foundation cracks usually develop during the first few years after construction finishes, as the building settles and the concrete finally cures. They typically start as hairline cracks that progressively open up. A structural engineer is able to measure their movement, and to determine whether the cracks are new developments, or older history.

It is also possible for basement wall cracks to develop when peripheral events affect an existing structure. These could include alterations to the property, blasting in the neighborhood, or even an earth tremor. It’s important to monitor for basement cracking during events like these, so that an insurance or other claim may be lodged before the opportunity expires.

Consequential Problems

Most times a mildly cracked foundation wall is more of an irritation, because it admits moisture and even drops of water through it. Nonetheless, homeowners are strongly advised to consult an a qualified contractor or engineer if in any doubt. The more serious consequence is often a reduction in the value of their home, since buyers often run a mile from the sight of cracks.

“Solutions” That Don’t Always Work

The only sure-fire way to seal a leak is at its source (unless it’s a hairline crack that may be filled with polyurethane). As a professional foundation contractor in Toronto, we get hundreds of calls a year for foundation cracks, including following up on poor attempts to fix them.  The following are examples of botched jobs we often come across:

  • Amateurish attempts like papering over basement wall cracks or filling them with commercial caulking seal. These are inevitably bound to fail as efflorescence builds up behind the sealant causing it to peel away. It’s also almost impossible to obtain a dirt-free, perfectly dry surface with which to bond.


  • Commercial filling with hydraulic cement or other rigid substances is also bound to fail, because the structure will still shift with seasons, while the hydrostatic pressure from outside continues unabated. The same applies to epoxy seals to a lesser extent. They may sometimes work for years though – provided they are attached to a perfectly clean dry surface

Flexible, expandable urethane sealants may work where a crack has stabilised. However their elasticity is limited, while cracks can expand by up to 100% quite quickly. For this reason they are not ideal.

The Real Solution

Where vertical foundation wall cracks are serious, or there’s water pouring through them in the rainy season, the only viable solution is to remove the outside soil, to install a french drain or other soak-away system, and to apply a flexible waterproofing sealant or membrane from the outside.

Repairing and/or waterproofing a foundation  can be expensive for the homeowner, it’s also alot of work. If you’re going to do it, be sure it’s being done by a professional that will offer a guarantee on their work and has experience working with foundations.



Did you know that the city of Toronto sits on top of a labyrinth like maze of ancient rivers and sewer systems that have long been forgotten about?  While there are many reasons your Toronto basement might be leaking water, in some areas, rising water tables could be the problem.  While the water table below your home may be several meters below your foundation, that doesn’t mean that it won’t cause water problems in your basement.  Below explains what a water table is and how it can effect your home.

A water table – sometimes also referred to as a groundwater table – is the upper level of accumulated water that has collected on the saturated or impermeable surface below it. Groundwater tends to level out just like the water in your bath or swimming pool. That’s why it’s called a table by the experts, because the tops of tables are usually smooth too.

High water table in Toronto from underground rivers and streams

Two Types of Water Tables

Geologists speak of two kinds of water tables, namely perched ones and true ones. True tables are those prevailing in an area. They represent the average water height, plus / minus the prevailing season in terms of wet or dry. However water doesn’t always seep down consistently. Factors that affect water penetration include:

  • The degree of existing saturation
  • The permeability of the strata
  • The presence of impermeable rock.

Groundwater may perch higher at some points than others as a result of this phenomenon. Think of this as a step-change, or as if there’s a thick book laying on your desk or table.

Implications for Building Basements

Homeowners watching their new basement being excavated should not necessarily be content when the earth comes out dry. That’s because water could rise up during the rainy season if their home is in a low-lying area, and exert hydrostatic pressure on the walls resulting in leaks and cracks in your home’s foundation.

This is especially probable if their house is built on clay, or if they have to excavate through hard rock or shale to create space for the basement. That’s because excessive rain could cause water to perch around it temporarily, inevitably increasing the risk of mould-inducing dampness.

Artificial Causes

Basement contractors dig out a larger area than they require, so they can work on both sides of the walls as they damp or waterproof them. When they are finished, they backfill the spaces on the outside of the basement, usually with the same material they previously excavated.

This creates a leaky fill especially if they’re using rock or shale that water filters through more rapidly that the original underlying surface can absorb. This in turn creates a dam of wet material right around the outside basement walls. This can stand for days or even weeks in winter. Just imagine the hydrostatic pressure if you filled the space with water, and you’ll have a good idea of the consequences.

Prevention is Better Than Cure

If you are looking for a home and are concerned about water problems, or you currently have water problems in your basement, you need to consider a four-pronged strategy to knock this problem on the head. Ignore this advice at your peril. You could be inviting a high repair bill in the future.

  • Avoid building/buying your house – or add a basement – in a low-lying area that’s surrounded by high ground or where water drains to naturally.  Water will use gravity and  find the path of least resistance when searching for a low lying area, which could be that new home you’re eyeing.


  • Do install french drains / weeping tiles around the outside walls at the lowest point, to drain groundwater away before it causes damage.


  • Do not allow the contractor to backfill with loose material.  Be sure the backfill is replaced properly or you could be creating a swimming pool around your foundation. If necessary, import something more suitable.


  • Do everything you can to prevent water from finding its way from the surface to the bottom of your outside basement walls in the first place.

In these ways it is usually possible to manage groundwater effectively. Ignoring a water leaks in your basement for too long can lead to expensive repairs and health concerns from mold later on down the line if left untreated.

image courtesy of Environment Canada



If you walk in mist or fog and your clothing becomes wet, you feel a sensation of dampness on your skin – unless of course you are wearing a water-resistant garment. In pelting rain the water will force itself past the fibers, and start pouring down your arms and legs.  That’s why sailors aboard ships wear sou’westers, not scotch-guarded pullovers.

A similar principle applies to homes and basements. Damp-proofing is a lightweight treatment that helps prevent the moisture in the soil from penetrating through a basement wall or floor. However, if there’s a possibility of underground water damming up from time to time, then water-proofing is the only practical solution.

Why Is That?

The difference is a thing called hydrostatic pressure. When you were at school your teachers probably tried to explain that the pressure exerted by a column of water is equally exerted in all directions. This means that the weight of damp earth outside your basement applies an incredible force to its retaining walls, and can force the moisture in through any cracks as if it’s a pump.

This same pressure ensures that most basement walls and floors eventually fracture (although this may sometimes present itself as mere hairline cracking). As the ground-water begins to find a way through the fractures more and more water takes its place, creating a steady trickle if nothing is done to impede the flow. Under these circumstances traditional damp-proofing methods are useless, for reasons mentioned below.

Why Damp-Proofing Fails

Builders customarily apply an asphalt-tar solution to any outside wall that’s below ground level. This is to meet Section 406 of the International Residential Code that specifies this as the bare minimum. While this may be adequate in dry, hot areas, it seldom suffices in Canada, where expansion and contraction between winter and summer seasons causes it to crack (especially over existing cracks in walls and floors).

Why Water-Proofing is More Successful

Water-proofing on the other hand is a material that’s mainly made from natural rubber, which means that it’s environmentally friendly. Moreover, as your basement flexes and cracks open and closed again, genuine water-proofing stretches and shrinks in harmony, so that it keeps on doing its job.

The Extra Cost  is Worth It

The budget-end of basement builders sometimes maintains that damp-proofing is equally good – and cheaper too. But then it’s not their problem when it fails, because they’re not responsible for the power of nature, and where you chose to build your home. When that happens there’s only really one solution. And that’s to remove every square inch of cheap damp-proofing, and water-proof your basement properly from scratch.

In Ontario, You Really Don’t Have Much of a Choice

Ontario’s prevailing climate with longer, usually frozen winters, and temperate summers in the south is an open invitation for basement walls and floors to crack. If you are building a new basement this means that you need a specialist to water-proof it for you. On the other hand, if you’re already experiencing leaks and dampness because of previous substandard damp-proofing, then the same logic applies again. If you’re experiencing water problems in your basement and are thinking about a solution, waterproofing methods is simply the better choice as a long term solution.


Water is a mighty powerful and persistent thing. It’s carved out canyons and has flooded huge cities. Allow it drip for long enough and it will punch a hole through granite. When it comes to your basement – if there’s a way for water to find it’s through, trust me, it will discover it and you’ll soon have a leaking basement  problem.

That’s why so many of Toronto’s basements suffer from some form of basement water problem. Causes of this can range from leaking water wells and cracked walls, to porous and cracked floors. Left untended, basement leaks can lead to all kinds of associated problems, ranging from mold and mildew, declining property values, to a family with an entire floor of their home that is unhealthy and unusable.

Sump pump installed in Toronto home

Two Options

There are only two solutions to a leaky basement. The first is to stop the water getting in. The second is to manage it (more about this later). Any competent car mechanic will confirm that the only way to stop an oil leak is at its source. The same applies to basements (choosing a mechanic and a contractor should be taken with equal care).

Unfortunately, when basement water-proofing fails from the interior, there’s no easy way to stop it because the source is on the far side of a brick/concrete wall, or under a concrete foundation deep below the ground. This makes accumulating the water in a hollow called a sump usually the first course of action. When it’s accumulated, you can lead it away with an electric pump.

Sump Pumps

A sump pump is not unlike a water-feature pump in principle, in that it’s connected to an electricity supply, but always under water so it never develops an airlock. The sump is equally simple. It’s just a hollow you could squeeze a beach ball into, and covered over with a lid so everything looks neat and tidy.

The system is controlled by a float that’s not unlike the one in your bathroom toilet (at least in principle again). When the water reaches a set level, a switch turns on the pump for as long as necessary to control the water in the sump. By far the larger challenge is leading the leaking water to the sump in the first place. But that’s a subject for another article.

Do I Need a Sump Pump?

You need a sump pump if there’s an accumulation of water in your basement at any time of year. They’re not all that expensive. Besides, if you ignore the damp, mold could become the least of your problems. Your basement den or bedroom could become permanently uninhabitable. Imagine what that would do to your property valuation, and the value of what is probably the biggest investment you’ll ever make.

A Permanent Solution

If you have permanent bronchial problems, you could be living in a damp environment. If your basement is permanently damp, then that’s a sign of a deeper-seated problem too. Once you have successfully stabilized your situation with a sump pump, you really should call in a registered and experienced basement waterproofing expert. They will advise you on a longer term solution that retains the integrity of your home.