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Why Are Cracks in My Basement Floor?

Crack in basement floor

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So you’re looking around your house, and you see these long cracks in the floor of your basement. You may very well ask, “What’s going on? Why are there cracks in my basement floor?”
These cracks may have several possible causes, and such cracks do not mean that your house is about to fall down. We’ve taken a moment to share these causes with you so that, hopefully, you’ll know what they are the next time they come up.
Read on to learn more about common causes for cracks in your basement.

Table of Contents

What Causes a Cracked Basement Floor?

Cracks are normal in house foundations. Many causes exist for cracks to form, including home foundation settlement, concrete shrinkage, curing stress, and poor construction.
Many homeowners panic when they first see these mysterious cracks running across their often-forgotten basements. As it turns out, most cracks in your basement are normal and may not need significant repair. However, some can cause moisture and toxic gases to enter your home, endangering the health of your family.
So what exactly causes a cracked basement floor? Here are some common causes.

Poorly Compacted Soil and Loose Backfills

On starting construction, builders dig a hole into compact virgin soil to make room for your house’s foundation. If the soil is poorly compacted during any part of this process, the loose backfill can wreak havoc on the concrete slab—hence the cracks in your basement floor.

Soil Washout

When a plumbing leak occurs in your home, it can cause structural problems and erosion. This is because rainwater can seep through the cracks and wash away the soil surrounding the leaky pipes.
The resulting void means that nothing is supporting the home’s concrete slab anymore. In time, this leads to both cracks in basement floors as well as settlement of your home’s foundations.

Found a crack? Stop Them From Expanding. Contact MT Drains

Our team of experts have been servicing Vaughan and the surrounding area since 1991.

Poor Drainage

To prevent your basement floor from cracking, you should take steps to relieve the hydrostatic pressure of water on your home’s foundation. Improper grading and poor drainage can cause buildup around the foundation, which puts stress on it, leading to cracks in your basement.
To reduce this impact, homeowners can implement simple measures like creating a well-graded yard, installing a sump pump, or installing proper drains for excess water runoff.
basement sump pump cover

What Do the Common Types of Basement Cracks Mean?


Spalling (patches of surface flaking) occur when water works its way to the top layer of the basement floor during curing, weakening that part of the floor, which then loosens and flakes off. Although unattractive, it doesn’t urgently affect the integrity of a concrete slab since it should still be in good shape.

Hairline Cracks

If you notice hairline cracks in the basement floor of your newly built home, do not panic. These types of cracks can show up as long as a year after the construction team first poured the slab. They are entirely superficial and do not require repair.

Cracks Wider Than 1/8-Inch

Small to medium-sized cracks in your basement floor are natural and should not worry you. These do not indicate a larger problem.
Cracks greater than 1/8 of an inch wide will require sealing with masonry and concrete-specific elastomeric caulking sealant. This sealant will keep dangerous soil-borne gases such as radon gas, unwanted moisture, and unpleasant smells from seeping into your home.

Foundation Settlement Cracks

Over time, the foundation of a building can develop cracks or sink into uneven areas that are potentially dangerous. Professionals use polyurethane products to lift and stabilize sinking slabs to ensure safety when walking on them.

Cracks Combined with Heaving

Heaving cracks in the basement floor mean that you have a bigger problem to address. Clay soils and wet conditions can cause these cracks because they create pressure on the concrete slab, causing it to lift and crack.

Cracked Floor Joist, Basement Floor

Floor joists are the horizontal framing members that make up the skeleton of a floor frame. They span across rooms while supported by load-bearing walls or beams. Excess moisture, soil shifting, or poor spacing of support columns can weaken floor joists and beams. These conditions commonly manifest as uneven floors and cracked walls.

How to Fix Cracks in Basement Floors

Cracks Caused by Pests

Whether it is mice, rats or cockroaches that are causing a nuisance in your home, they have nowhere to go but your basement if the floor has cracks with water damage below. Forget about waiting until these pests invade your home.
Contact our team at MT Drains & Plumbing for a free inspection today.

Cracks Caused by Structural Problems

Concrete basements are not immune to damage. Extensive cracks can affect the structural integrity of a home, while smaller ones caused by soil shrinkage rarely do so.
If you notice massive gaps in your basement floor, our experts at MT Drains & Plumbing can inspect them right away to assess the potential for greater damage.

Cracks Caused by Water Seepage

Cracks in your basement floor can cause water seepage. The ground underneath the foundation is full of moisture, so when cracks exist, water can force its way up into your basement, causing hard-to-treat problems like mould and bacteria growth.
Our team of experts will install a waterproof membrane to prevent future flooding and protect you from unnecessary expenses further down the road.

Get in Touch with Our Basement Professionals at MT Drains & Plumbing

Cracks in your basement floor typically occur due to flooding, water seepage, soil shifting, or structural problems. Let our experts at MT Drains & Plumbing deal with your cracked basement floor.

We have over 20 years of combined experience in basement waterproofing and repair, and we know what it takes to ensure you gain control over your basement space once again. Our professional, friendly technicians who understand how stressful cracked or flooded basements can be are standing by to help you take care of these issues for good!
Schedule an appointment with our MT Drains & Plumbing team today at (905) 761-5551, so we may fix this problem for good! We serve Vaughan, Ontario, and the GTA.

Paul S

Paul has more then 20 years in basement waterproofing and plumbing projects experience. Looking for an advice from an expert plumber? Make sure to read Paul's articles about residential waterproofing and plumbing projects in Toronto.

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