Why Do Foundation Walls Crack?

While masonry or unreinforced concrete foundation walls are solid vertically, their resistance to pressure from the side is quite limited. Builders have designed the majority of residential foundation walls empirically – dry backfill height vs. wall thickness.

In some cases, the pressure against the wall increases by as much as 15% if the adjacent soil becomes saturated. This is enough to crack the foundation.

Frost can take hold if the water remains in the soil in winter. This leads to multiple pressure growth.

Main Reasons for Saturation of the Soil

Here are the main reasons why the soil around the house can become saturated:

  • The grading is level or slopes back toward the house
  • Broken underground sprinkler systems or water mains
  • A clogged perimeter foundation drainage tile
  • Rain water leaders are not extended out from the foundation

The wall will probably keep moving unless the structural problem is identified and remedied. A common solution is a urethane or an epoxy injection, but it won’t work on its own.

Types of cracks

Let’s have a look at some of the most common types of cracks that appear in foundations.


Stair Step

Stair-step cracks often appear in block foundations. They tend to occur along mortar joints. They are dangerous if they can fit more than a quarter.

Horizontal Cracks

These are also a cause for concern. The most common cause is water and unbalanced soil putting pressure on the foundation wall. There might be a leak in your basement, or you might notice the foundation caving inward.

Horizontal cracks are common in many parts of Canada. They are found around the frost line below grade. The cycle of freezing and thawing in winter usually causes them. The crack will appear over time due to the unbalanced pressure on the wall.

Like stair-step cracks, horizontal cracks do not tolerate delay. Get in touch with a foundation crack expert as soon as possible. A true professional will be able to repair such cracks permanently with a lifetime guarantee. If you decide to sell the house, they can provide a transferrable warranty.


New foundations are vulnerable to hairline cracks. They appear as the foundation settles and dries, usually within a year of construction. On the plus side, they tend to be cosmetic and don't cost much to fix.

Contact the house builder if you bought the house recently and noticed a hairline crack in the foundation. Your warranty might cover the repair. Monitor progression and take photos to document.

Diagonal Fracture

Usually, diagonal fractures aren't a serious threat to the foundation's structural integrity. As the wall settles, the natural curing process will have them as a result. The most they will run is 30 degrees vertically.

Usually, they can be fixed by injecting the epoxy. The solution is not expensive. Take a picture and record the date if you see a diagonal crack. It's only concerning if you can fit more than a quarter in the crack. In about half a year, contact a foundation expert in case the crack has continued to grow.

Vertical Fractures

These are less serious than horizontal ones and pose no structural risk. Usually, they run up and down the wall straight and are typical of poured foundations. They are commonly found in basements as well. Concrete curing or foundation settling causes them.

Injecting polyurethane or epoxy is the most common repair. No immediate danger exists if you can't fit a quarter in the vertical crack and there is no moisture.

Crack from Shrinkage

When a poured foundation starts drying and losing moisture, shrinkage foundation cracks will appear, the same way hairline cracks do. Newly built houses can develop shrinkage cracks within the first year. They are usually vertical and do not present a risk to the structure of the foundation.

If there are high radon gas levels in your area, there is a risk of it leaking into your basement. Your home warranty might cover shrinkage cracks in the foundation. If it doesn't, take a picture to document the crack. If more cracks start to appear or an existing one grows, consider an epoxy injection.

Non-Structural Cracks

Non-structural cracks are not a risk to foundation structure, as the name implies. The worst they can cause is leaks when the snow melts or there's a rainstorm. Water leaks in the basement can be a serious issue, although there is no structural threat. They can ruin walls, items, and floors and lead to mold growth. Moreover, the cracks will get worse if they are not addressed. Even an insignificant crack should be attended to eventually to prevent water from seeping into the house.

As concrete cures, small cracks will appear in the walls. They are subject to a cosmetic repair. The crack might not be structural if it runs diagonally or vertically and is 1-2 mm wide.

Non-Structural Wet Fissure

This type of fissure happens due to foundation shrinkage. Water evaporates from the concrete soon after one pours the foundation. The extent of shrinkage is directly proportional to the initial wetness of the concrete mix, making cracks more likely to appear. Concrete's natural setting can also result in fractures to the foundation.

A professional can use urethane to seal foundation cracks that are leaking actively or are wet. This substance is quite flexible and easy to inject into the fissure. It will grow to fill the cavity as water comes into contact with it.

If you see moisture or water seeping from a crack, you must act swiftly, especially if you live in an area with volatile climate conditions. Such weather patterns can result in more severe problems with the water or make the crack wider.

Cracks in the Foundation Slab

With time, poured concrete slabs will start cracking. This happens for three main reasons:

Slab Settlement

You have a problem when a new foundation slab starts settling. Low-quality work might be the reason. They didn't compact the ground underneath the slab. Another reason might relate to bad soil conditions. Don't hesitate to contact a professional.

Concrete Setting

The natural setting, drying, and curing of the concrete slab is another common cause. This is far more preferable to the first as it poses no structural threat.

Frost Heave

Finally, frost heave can impact slab foundations at or above grade. The concrete can buckle after water freezes underneath the slab.

Get in touch with a professional if the crack is bigger than a hairline. They will consult you and make suggestions for repair options.

Crack in the Structural Foundation

These fractures are a danger to the home's structural integrity. If they are wider than a quarter of an inch and horizontal, it's a sure sign of a structural defect. Usually, these cracks are caused by movement, whether it's due to the soil shrinking, pressure on the soil, or temperature changes.

A professional can use epoxy to repair the crack in this case, but it probably won't be enough because the crack was initially caused by stress due to movement, which will not stop. You will likely need additional reinforcement to the foundation in the form of straps or staples made of carbon fiber. In the absence of such, the crack will keep growing.

Measures to Prevent Cracks in Your Foundation

Water problems in your basement are not merely annoying; they can cause illness. Your basement is useless if it suffers from periodic flooding. You can’t control water, only manage it. A protective board can waterproof the basement foundation.

The most popular waterproofing method for basements is exterior foundation waterproofing. This stops water from seeping into the basement from the outside. The area affected is closed off from the exterior and cleaned, and the insulation material is then brought onto it.

To protect against groundwater, perched water, or nuisance water, a professional will apply waterproofing to the foundation wall. This will also stop methane gas or contaminated vapor from seeping in through the sides. A drainage and protection board can be applied over the waterproofing material as a second line of defense.

Inspection of the Weeping Tiles

In most cases, weeping tiles are made of plastic or clay. These pipes encircle the foundation base, collecting any pooling water. They are connected to either a sump pit or a sewer. Most modern houses have sump pumps and pits.
A professional should inspect and check for the proper functioning of the tile system after the waterproofing and protection board are installed. This is of paramount importance because groundwater will get into the basement without a place to drain.
If the tile system isn’t working, here’s what can be done:

A professional will try to flush out the system with high-pressure water. If this doesn’t work, you can have a sump pit and pump installed in the interior. A tile section will line the part of the foundation wall that is being repaired, forming a connection to the sump pit.

Typically, a pump with 1/3 hp is enough to control groundwater. These pumps discharge sufficiently. The sump pump must be equipped with an alarm.

Want to speak with a professional regarding your foundation wall? 

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