To fix a crack in foundation walls yourself, first check three things: the crack is thin (under about 2 mm), it is dry, and it has not grown. If all three are true, you can clean it and seal it with an injection kit or a cement-based patch. If the crack leaks, is horizontal, is offset or keeps widening, stop and hire a foundation contractor or a structural engineer.
Step one: work out what kind of crack you have
Most people ask how to fix the crack before they know what it is. The repair depends on the type. Spend a week measuring before you buy any product.
Wet or dry
A wet crack shows damp stains, white mineral deposits (efflorescence), or water beading on the concrete after rain or snowmelt. Water finds the crack because the crack is a weak point in a wall that is under pressure from wet soil. The crack may be harmless to the structure and still cause real damage to finishes and air quality.
A dry crack shows none of this. Many dry cracks are shrinkage cracks that formed as the concrete cured, often within the first years after the house was built.
Structural or cosmetic
A structural crack shows that the wall or footing is moving. Watch for these signs:
- The crack is horizontal, or runs in a stair-step pattern through concrete block.
- The crack is wider at one end, or one side sits proud of the other (offset).
- The crack keeps widening over weeks or months.
- Doors and windows stick, or floors slope, in the rooms above.
Engineering firms in Ontario use similar lists. For example, an Ontario soil engineering guide on horizontal foundation cracks treats horizontal cracking, growth and offset as the red flags. Thin vertical cracks near corners and window openings are the common cosmetic type.
How to monitor a crack
Use a pencil to mark both ends of the crack and write the date. Measure the width with a crack gauge or a ruler with fine markings. Take a photo with a coin beside the crack for scale. Check it again after the spring thaw and after a heavy rain. A crack that is the same size after several months is a much better candidate for a simple repair than one that has moved.
What a homeowner can safely do
A few jobs suit a careful homeowner. All of them assume the crack is stable and the wall is not bowing or leaning.
Seal a dry, thin, vertical crack
This is the most common DIY job. The steps are:
- Clear loose concrete and dust with a wire brush and a vacuum.
- Pick a product that matches the goal. Epoxy injection kits are rigid and bond the two faces. Polyurethane kits stay flexible and suit cracks that may leak. A cement-based patch is enough for a surface hairline.
- Follow the maker’s technical data sheet for temperature limits and cure times. Many injection materials do not cure well in a cold basement, which matters in an Ontario winter.
- Inject or fill, let it cure, and scrape the surface smooth.
- Keep watching the crack. A repair that cracks again beside the old line tells you the wall is still moving.
A DIY kit fixes the crack. It does not fix the reason the crack formed. If water sits against the wall because of poor grading or a blocked downspout, the crack can return.
Fix the outside causes
These are the safest and often the most useful jobs:
- Extend downspouts so they discharge well away from the wall.
- Regrade the soil so it slopes away from the house.
- Clear window wells and check that they drain.
- Keep large trees and heavy planting beds back from the foundation if you can.
Water management costs little and lowers the pressure on the wall. Do it before, or along with, any crack repair.
Small surface jobs
You can patch a stable hairline crack in a parged (cement-coated) wall, paint over old sealed cracks, and monitor with a gauge. Hold off on any wall finishing, such as new drywall, until you have watched the crack for a full season.
What needs a contractor or an engineer
Some work is not a DIY job, and a bad guess can cost far more than the repair.
- Leaking cracks. Injection into a wet crack, and the correct choice of material, is a trade skill. A professional can inject from the inside with polyurethane. If the leak comes from poor drainage outside, they may propose exterior work instead.
- Horizontal cracks and bowing walls. These point to lateral pressure from soil. Repairs such as wall anchors, carbon fibre straps or steel beams need an engineer’s design.
- Stair-step cracks in block walls, or offset cracks. These often mean settlement. A contractor should not guess at the cause.
- Cracks that keep growing. Growth means the cause is still active.
- Cracks with mold. If you see or smell mold, the air quality issue is separate from the crack, and the moisture source needs fixing too. See mold removal companies in Ottawa for one board of contractors that do that work.
Contractor or engineer first?
A short rule: if the crack looks like a moisture problem, start with a contractor. If it looks like a movement problem, start with a structural engineer. Contractors who sell repairs have an interest in selling a repair. An engineer who charges for an assessment does not. Ask for a written scope in either case, and avoid any quote given by phone without a site visit.
Decision table
| What you see | Likely type | Homeowner job? | Who to call |
|---|---|---|---|
| Hairline crack (under about 2 mm), dry, vertical, unchanged | Shrinkage | Yes, seal and monitor | Nobody yet |
| Thin vertical crack that seeps after rain | Wet, likely non-structural | Only for a minor seep | Waterproofing contractor |
| Crack wider than about 6 mm | Possible movement | No | Engineer, then contractor |
| Horizontal crack or bowing wall | Lateral soil pressure | No | Engineer |
| Stair-step crack in block, or offset faces | Settlement | No | Engineer |
| Crack that grows between measurements | Active movement | No | Engineer |
| Crack plus mold or musty air | Moisture and air quality | No | Contractor and mold specialist |
The thresholds are common rules of thumb, not code limits. A building inspector or engineer decides for your house.
Typical costs in Ontario
Prices vary by region, access and the state of the wall. The figures below are typical ranges from published Ontario price guides. They are not quotes, and you should get several written ones.
| Job | Typical range | What drives the price |
|---|---|---|
| DIY injection kit and tools | Modest hardware store cost | Kit size, number of cracks |
| Professional injection, per crack | About $500 to $1,200 | Crack length, wall access, epoxy or polyurethane |
| Structural reinforcement | About $1,500 to $5,000 | Engineer design, number of walls |
| Waterproofing and sealing work | About $2,000 to $6,000 | Interior or exterior, length of wall |
| Severe cases such as underpinning | Can reach $10,000 or more | Depth, access, permits, engineering |
Exterior repairs need digging, so they cost more than interior injection. Some contractors also charge more for winter work. Ask each bidder to say what causes the price and whether it includes an engineer’s letter, permits and a warranty.
Toronto and Ottawa: what the ground does to your wall
Toronto and much of the GTA sit on clay-rich till and clay soils. Clay holds water, swells when wet and shrinks when dry, and pushes on basement walls. Ottawa is different in one important way: much of the city sits on Champlain Sea clay, which is sensitive to moisture changes and to trees drawing water from it. Both cities also have freeze-thaw cycles that open small cracks each winter and spring.
I found no Ottawa foundation repair board in our data for this month. The nearest ranked boards for that city are basement waterproofing and mold removal, so the numbers below use those.
What our boards show for Toronto and Ottawa
The directory ranks companies by Google rating and review count. Here is the data for September 2026. It describes the companies, and it is not an endorsement of any of them.
Toronto. The foundation repair companies in Toronto board ranks 20 companies. The median rating is 5.0 and the median review count is 76. Together the 20 have 5,345 reviews, and 3 of them have fewer than 20. The basement waterproofing companies in Toronto board also ranks 20, with a median of 100 reviews, 3,989 reviews in total, and none under 20.
Ottawa. The basement waterproofing companies in Ottawa board ranks 20 companies. The median rating is 5.0 and the median review count is 56. The total is 1,394 reviews, and 5 companies have fewer than 20. The mold removal companies in Ottawa board ranks 20 with a median rating of 4.8 and a median of 32.5 reviews, and 6 have fewer than 20.
What this means when you choose
Ratings alone tell you little here. Toronto’s median is 5.0, so most companies sit at or near the top. Look at review counts. A company with 8 reviews and a 5.0 rating has a very thin record. A company with several hundred reviews at 4.8 has a longer one. The Ottawa boards are thinner, so a review count under 20 is common and not a red flag by itself.
Use the boards to build a shortlist, then check each company directly:
- Read recent reviews for crack or leak jobs, not just the star average.
- Ask what method they propose and why, and whether an engineer reviews structural work.
- Ask for the written scope, the warranty terms and proof of insurance.
- Get at least three quotes after a site visit.
The full list for this trade is on the foundation repair hub. You can also compare other towns, such as foundation repair companies in Hamilton, if you live outside Toronto and Ottawa.
Before you start any repair
Do these things in order:
- Measure and date the crack, and photograph it.
- Note whether it is wet after rain or thaw.
- Fix the outside water sources: downspouts, grading, window wells.
- Decide with the decision table whether the job is yours.
- If not, book an engineer for movement signs or a contractor for moisture signs.
Do not cover a crack with drywall, paint or a finished wall until you know it is stable. A hidden crack cannot be monitored.
Frequently asked questions
Can I fix a crack in my foundation myself?
Yes, if the crack is thin, dry, vertical and has not changed for a long time. A hardware store injection kit or a cement-based patch can seal it. If the crack leaks, is wider than about 6 mm, runs horizontally or keeps growing, call a professional.
How do I tell a wet crack from a structural crack?
A wet crack lets water in, and it is a moisture problem first. A structural crack shows movement: it widens, is offset, runs horizontally or stair-steps through block. A crack can be both, so measure it and watch it before you pick a repair.
How much does professional foundation crack repair cost in Ontario?
Published Ontario price guides give roughly $500 to $1,200 per crack for injection. These are typical ranges, not quotes. Access, crack length, the injection material and whether an engineer must look first all change the price.
Who should I call first, a contractor or an engineer?
Call a contractor for a dry hairline crack or a simple leak. Call a structural engineer first if the crack is horizontal, offset, wider than about 6 mm or growing, or if doors and floors have shifted. The engineer’s report then tells contractors what to bid on.