Foundation crack repair kits can work on a narrow, dry or slightly damp crack in a poured concrete wall that is not moving. They often fail on cracks that leak under pressure or that widen with the seasons. A kit seals the crack, but it does not remove the water pressure or the movement behind it. If the crack leaks after rain, treat the kit as a short-term patch and get the cause checked.
What is in a foundation crack repair kit?
Most kits sell one of two materials. Both are injected into the crack through small ports fixed to the wall. Only the basic idea is the same.
- Polyurethane kits use a two-part hydrophobic foam or grout. It reacts with water, expands and forms a flexible seal. Sellers describe this foam as expanding up to 20 to 30 times its original volume.
- Epoxy kits use a two-part resin that cures hard. It bonds to clean, dry concrete and can restore some strength across a crack.
Kits include a surface sealer (often called a paste or a gel), plastic injection ports, a cartridge or bottle of resin and a mixing nozzle. You seal the crack face, fix the ports along the crack, then inject from the bottom port up until material shows at the next port.
The kit is only one part of a repair. Wall prep, crack width, temperature and water pressure decide most of the result. That is why two homeowners can buy the same kit and get opposite outcomes.
When do crack repair kits work?
A kit has a fair chance when all of these are true:
- The wall is poured concrete, not concrete block.
- The crack is narrow and straight. Hairline cracks and cracks of a few millimetres suit most kits, so read the width limit on the product you buy.
- The crack is stable. It has not grown, and it shows no step, offset or horizontal line.
- The crack is dry, or only damp. It does not run with water.
- You can reach the crack from the inside and the surface is clean and free of paint, efflorescence and loose concrete.
Many vertical shrinkage cracks in poured walls fit this description. Concrete shrinks as it cures, and these cracks often form in the first years after the house is built. They are common, and many are not structural. A stable, dry shrinkage crack is the best case for a DIY kit.
Even then, keep the result in perspective. A kit that holds for one winter has not proved anything yet. In Toronto, walls go through freeze and thaw cycles and wet springs. Watch the repair through at least one spring thaw and one heavy rain before you call it done.
Why kits fail on actively leaking cracks
Most kit failures come from water, not from a bad product. There are four common reasons.
Water pressure pushes the material out
When soil around the foundation is saturated, water pushes against the wall. This is hydrostatic pressure. Water moving through a crack under pressure can wash uncured resin out of the crack, or stop it from filling the full depth of the wall. A crack that runs during a rainstorm is under this kind of load.
Epoxy needs a dry crack
Epoxy does not bond well to wet or damp concrete. Injected into a leaking crack, it can fail to cure properly or fail to stick to the crack faces. Contractors who write about injection say the main pitfall of epoxy is that it only suits cracks that are completely dry.
Polyurethane can stop a leak but not the cause
Polyurethane is designed to work with water, so it is the better choice for a wet crack. But it does not suit every situation. Product sellers and trade sources note it performs poorly in freeze and thaw conditions in some cases and when the water table is high, and that it is not for structural reinforcement. It also seals only what it reaches. If water finds a new path through a cold joint or a second crack, the leak moves.
The crack keeps moving
Soil in the Toronto area includes clay-rich material that swells when wet and shrinks when dry. Frost also acts on shallow footings. If the wall moves, a rigid epoxy fill can crack again beside the repair. A flexible foam tolerates more movement, but a crack that keeps widening needs a diagnosis first. A kit cannot tell you why it moves.
Epoxy or polyurethane: which fits which crack?
| Situation | Epoxy kit | Polyurethane kit | Call a professional? |
|---|---|---|---|
| Dry, stable, narrow crack in poured wall | Can suit; adds bond strength | Can suit | Not always |
| Damp crack, no active flow | Poor bond risk | Can suit | If it returns |
| Crack that leaks after rain | Not suited | Short-term stop possible | Yes, check the water source |
| Crack that keeps widening | Likely to re-crack | May tolerate small movement | Yes, get a structural check |
| Stepped or horizontal crack, bowing wall | Not suited | Not suited | Yes, promptly |
| Concrete block wall | Not suited to most kits | Not suited to most kits | Yes |
| Floor crack or floor and wall joint | Varies by product | Varies by product | Often |
This table is general guidance. Read the limits on the product you buy, since kits differ. Where the manufacturer sets a crack width or temperature limit, follow it.
Warning signs that a crack is more than cosmetic
A crack is more serious when it shows any of these signs:
- It is wider at one end or has grown since you first marked it.
- One side of the crack sits proud of the other.
- It runs horizontally along a block wall, or the wall bows inward.
- It leaks or seeps after rain or during the spring thaw.
- Doors or windows above it stick, or you see cracks in the brick outside.
Mark the ends of the crack with a pencil and date them. Photograph it with a ruler beside it. Check again after a month and after the next heavy rain. This costs nothing and gives a contractor useful facts.
If you see white powder on the wall, that is efflorescence. It shows moisture moves through the concrete. It is not proof of a structural problem, but it does tell you the wall is wet at times.
What professional crack injection involves and costs
A professional injects from the inside, and often checks the outside for the water source: grading, downspouts, window wells and drainage. Most injection crews use commercial two-part resins and pumps, not a hand caulking gun, so the material can fill the crack under pressure to the full wall thickness.
Cost depends on crack length, wall type, access and whether the crack is structural. HomeStars lists crack injection in Toronto at roughly $450 to $1,100 per crack, and its pages note that block walls cost more than poured concrete. These are typical ranges, not quotes. Get a written quote that says what material is used, how much of the crack is covered and what the warranty covers.
Some contractors also warn that injection is not a fix for a wall with a drainage problem. If several cracks leak, or if water comes in at the floor joint, exterior waterproofing or interior drainage may be a better answer than repeated injection. See the trade hub for foundation repair for how the trades split.
What the Toronto boards show
The data below covers the boards on this site for September 2026. It ranks companies by Google rating and review count. It is data, not an endorsement of any company.
- The foundation repair companies in Toronto board ranks 20 companies. The median rating is 5.0 and the median review count is 76. Together they have 5,345 Google reviews. Three of the 20 have fewer than 20 reviews.
- The basement waterproofing companies in Toronto board ranks 20 companies, with a median rating of 5.0 and a median of 100 reviews. Together they have 3,989 reviews, and none has fewer than 20.
- The mold removal companies in Toronto board ranks 19 companies. The median rating is 4.9, the median review count is 74, and 5 have fewer than 20 reviews.
At the top of the foundation repair board, Groundworks Foundation Repair Toronto has a 4.9 rating from 1,739 reviews. Aquatech Basement Waterproofing Toronto has a 5.0 rating from 867 reviews, and RCC Waterproofing Toronto has 4.8 from 794 reviews.
What this means for you: ratings sit close together, since the median rating on two of the boards is 5.0. The review count is the better signal of how much evidence sits behind a rating. A 5.0 from 12 reviews tells you less than a 4.8 from 794. Read the recent reviews for words like “crack,” “injection” and “leak” to find companies that do this specific job. Then ask each company what it thinks caused the crack before it quotes a price.
If you live outside Toronto, the same ranking exists for nearby cities, such as foundation repair companies in Etobicoke, foundation repair companies in Mississauga and foundation repair companies in Markham.
How to decide: a short checklist
- Measure and mark the crack. Record the width, length and date.
- Check for water. Look after a heavy rain. A dry crack is a better kit candidate than a wet one.
- Check for movement. Wait a month, then compare with your marks.
- Fix the outside water first. Extend downspouts, clear window wells and check that the grade slopes away from the house. This costs little and reduces the load on every crack.
- Choose the material to match the crack. Polyurethane for a damp or leaking non-structural crack. Epoxy only for a dry crack where you need bond strength, and only if a professional agrees.
- Escalate early. If the repair fails once, do not repeat it. Call a professional and ask for a diagnosis, not just a second injection.
If moisture stays in the basement after a repair, check for mould, which can start on damp drywall and wood in a few days. Health Canada publishes guidance on mould in homes if you need to know when to seek help.
Frequently asked questions
Do foundation crack repair kits actually work?
They can work on a narrow, stable crack in a poured concrete wall, if you prepare the surface and follow the instructions. They often fail on cracks that leak under pressure or that keep moving. A kit treats the crack, not the water or the movement that caused it.
Should I use epoxy or polyurethane in a leaking crack?
Polyurethane is the usual choice for a leaking crack because it reacts with water and stays flexible. Epoxy needs a dry crack and does not bond well to wet concrete. Neither one fixes the cause of the leak, such as poor drainage or hydrostatic pressure.
How much does a professional crack injection cost in Toronto?
HomeStars lists about $450 to $1,100 per crack in Toronto. These are typical ranges, not quotes. Crack length, wall type, access and whether the crack is structural change the price.
When should I skip the kit and call a professional?
Call a professional if the crack is wider than a few millimetres, is growing, leaks after rain, or shows a step or a horizontal line. Also call if the wall bows inward. A pro can tell if the cause is structural or water related.