Tag Archive for: foundation cracks

Are Cracks In The Foundation Normal?

Toronto home with vertical crack in foundationPoets, lyricists, and other writers love the metaphor of the crack in the foundation, something that is small but the forerunner of pathological damage. A crack in your foundation is information—it is telling you something, and you must invest the time to figure it out.  It may turn out to not be a big problem, but it demands assessment.  It’s usually best to call in a specialist to make this assessment.  If you’re hesitant that they will try to sell you a suite of services and repairs, remember you can always get a free estimate or just say “no,” but that one thing is for certain—a crack, once present, will not go away and requires intervention.

It’s usually best to call in a foundation specialist to make this assessment as a foundation crack can be totally normal, or can be an indicator of something serious.  If you’re hesitant that they will try to sell you a suite of services and repairs, remember you can always get a free estimate or just say “no,” but that one thing is for certain—a crack, once present, will not go away and may indicate a more serious problem with your foundation.

HYDROSTATIC_PRESSURE (1)

Here in Toronto, foundation cracks are quite common.  Many foundation cracks are simple from shifting foundations and aging homes “settling” over time.  While others are from shoddy construction from the start or an environment surrounding your foundation that is contributing to its erosion.  As you can see, sometimes it’s nothing but other times it can be serious.

Even if the foundation crack is not serious, it can still cause water issues and can lead to foundation erosion over time if water is allowed to continuously channel through your foundation into your basement.

So, let’s take a look at some of the most common information—the most common causes—of basement foundation cracks.

 

Concrete Contraction

Concrete is a mixture of cement, water, and aggregate.  It is poured and then dries and cures.  Early in the curing stage, the concrete enters its plastic state.  In this state, it is still very moist, but it continues to lose moisture during the curing process.  Steve VandeWater, in his paper “Why Concrete Cracks,” illuminates, “because concrete is a very rigid material, this shrinking creates stress on the concrete slab.  As the concrete shrinks, it drags across its granular subgrade.  This impediment to its free movement creates stress that can literally pull the slab apart.”  He continues, “when the stress becomes too great for the now hardened concrete, the slab will crack in order to relieve tension.”

VandeWater points out that these plastic-state cracks are almost sure to occur near obstacles, objects placed in the concrete slab, such as drains, plumbing fixtures, etc.  The concrete has no ability to shrink around these objects.

 

Contraction cracks not a disaster

Fortunately, though some cracks due to the contraction of concrete during its curing process are inevitable, they aren’t likely to cause serious structural damage.  They’re mostly a nuisance, providing a gateway for things like water leaking or insects.

 

Exterior step crack Toronto home

Exterior step crack

Settlement

A second big reason for basement cracks is your house settling into the soil.  Daniel Friedman is a construction worker who discusses this issue.  He says that floor slabs need to be poured into “compacted fill” as opposed to “soft fill.”  To explain what this means, he clearly illustrates, “my first job in construction was raking a huge dirt pile out to ‘level’ inside of an already poured and built footing and masonry block foundation wall.  Once the dirt was roughly ‘level’ via my hand rake, the builder went ahead and poured his floor slab.  ‘Compacted fill’ was not in our vocabulary.”

Floor slabs not poured in this manner are more vulnerable to settling into the soil, and in the vocabulary of the business, “floating,” moving as the soil moves.

Yet, it’s just as often that the culprit is not construction workers at all.  Mother Nature will damage your foundation if you give her half a chance.  Too much rain will cause the rising groundwater to squeeze the house’s foundation.  The bad news is that dry periods are problematic, too, since dry soil shrinks, in turn causing you foundation to settle.

In Winter, groundwater freezing also causes pressure on your foundation, pressure that may lead to cracking.

One thing to do to attempt to combat the sorts of pressure described above is to improve the tensile strength of your concrete.  Tensile strength is the ability to withstand force that could pull something apart.  Strange though it might seem, concrete actually has fairly low tensile strength.  Improving it can be a matter of a contractor adding rebar of fiber to the concrete.

 

Horizontal crack in Toronto foundation home

Horizontal Crack

Horizontal Cracking

If the cracks you observe are horizontal, you should take them that much more seriously, since they are indications of serious structural problems.  Consultant Gary Fuller explains, “if the foundation does not provide enough lateral support, the walls will deflect inward and create horizontal cracking.”

Mike Holmes, host of the TV show “Holmes Inspection,” alerts us that horizontal cracking higher on the walls calls from water or frost, as “water from your downspouts or sump pump saturates the area, it freezes and exerts pressure on the basement wall.”

While there may not be one cure for basement cracks or one correct course of action, just be sure not to ignore the problem.  Take a lesson from the poets and don’t let the cracks spread and leave you on a foundation of rubble.

Why Are Cracks Appearing In My Foundation?

Foundation slab in Toronto basementDo you have cracks appearing in your foundation walls?  There can be many reasons for cracks to appear, some may be harmless, while others may be signs of serious problems.  The Bay Area is known for earthquakes, and the constant shifting of the ground can cause a foundation to crack over time.

A foundation is the substructure on which a building rests. In The Bay Area,  this is usually reinforced concrete although some elevated homes may be exceptions. The concrete sub-base can take two different forms. It could be a series of strips mirroring the walls above, or a solid sheet.

The correct application depends on the soil type. If it is stable, the strip method may suffice. However if the soil is clayey and likely to heave during wet periods, then the correct solution is a concrete “raft” that insulates the structure overhead from the movement that occurs below.

The Common Problem

Many builders design foundations on the basis that they will be stable once laid. Over time, outside forces make shift and put stress on the concrete structure:

  • The earth beneath the foundations settles because it was not properly compacted in the first place and ground water flows in through the gap
  • Earth movement occurs as a result of seismic events, mining activity or construction work on an adjacent site
  • The ground expands and contracts during alternating wet and dry seasons, especially if it has a clay component

When foundations move and crack below, this movement transfers to the structure above where masonry courses separate. It is most likely to be evident in the vicinity of weaker points like corners and above window and door frames.

Foundation crack Toronto home

Warning Signs

Unless caused by seismic activity, masonry cracking is usually a gradual process that occurs almost imperceptibly. Early indications can include:

  • Doors and windows that jam up in wet periods but begin to rattle in the wind when the weather’s dry
  • Cracks stepping up the masonry courses or appearing horizontally through bricks
  • In extreme cases, distorted walls and tilting chimneys

It goes almost without saying that these problems must be dealt with before serious structural damage occurs.

Remedial Action

While the ostensible cause of foundation cracking is ground movement or soil erosion, the true reason is that the foundation may be inadequate for local circumstances, or was earth around it was not settled properly before creating the foundation. Short of tearing down the structure the only practical solution is to strengthen the foundation. Foundation engineers achieve this with a variety of solutions that include steel or helical peers, plate and tie anchors, hydraulic lift slab piers and concrete underpinning.

In Summary

Cracks appear in foundations for two related reasons. Either the substructure is inadequate, or an event occurred outside the design specification. While the settlement may be slight and the visible evidence purely cosmetic, it may be the beginning of a far more serious problem if left untreated.

Some foundation cracks may not be an indicator of serious foundation problems, while others may signal the start of serious foundation problems.

Vertical Crack In My Foundation Wall

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.