Last updated: October 11, 2026. General information, not engineering advice. A crack that is growing, bowing or leaking heavily needs a professional assessment.
Crack injection is the professional alternative to patching: a technician fills a foundation crack from the inside with a liquid that cures in place. The two common materials are epoxy and polyurethane. Which one is appropriate depends on whether the crack is dry or wet, and whether it is still moving, and neither one fixes the reason the crack formed.
The short answer
Bob Vila describes epoxy injection as a method for stable cracks, such as those left after an earthquake or impact once movement has stopped, and polyurethane injection as an option for cracks that stay damp and cannot be dried. This Old House refers to epoxy or polyurethane foam as ways to seal cracks flexibly. In both cases, a professional should assess whether the crack is structural before choosing a material.
Epoxy vs. polyurethane, in plain terms
| Epoxy injection | Polyurethane injection | |
|---|---|---|
| Typical use (per Bob Vila) | Cracks that have stopped moving; two-part pressurized epoxy injected through ports | Cracks that stay wet and cannot be dried |
| Who does it | A contractor | A professional, similar to epoxy injection |
| Good question to ask | Has the crack stopped moving? How do you know? | Why is the crack wet, and where is the water coming from? |
| What it does not do | Does not address water pressure or soil movement behind the wall | Does not address water pressure or soil movement behind the wall |
We are deliberately not giving a head-to-head strength or lifespan comparison, because the sources we reviewed do not provide one. Ask any contractor you hire to explain, in writing, why they chose their material for your specific crack.
Why foundations crack in the first place
This Old House explains that hairline cracks often come from concrete curing and shrinking, especially in the first couple of years. Vertical cracks are usually settling as the house adjusts. Diagonal and horizontal cracks tend to point to differential movement or soil and water pressure against the wall. Injection fills the gap. It does not change the forces that opened it, which is why identifying the cause comes before choosing a material.
What injection can and cannot do
- It can seal a crack against water and, with the right material and conditions, bond a stable crack.
- It cannot stop a wall that is still moving, relieve soil pressure, or correct poor drainage outside.
- It may not prevent water from finding another route if the underlying water source is unchanged.
First, work out what kind of crack you have
- Cosmetic or hairline. Thin cracks from curing and shrinkage. Often not worth injecting.
- Serviceable. Cracks that show some stress and can admit pests or moisture. Not all need repair (Bob Vila).
- Structural. The rarest type, according to Bob Vila, and one that can compromise the house and must be fixed.
- Leaking. Seal the crack and handle the water source. Bob Vila recommends diverting water by removing plantings, adding gutters and downspouts, and sloping soil at least 2 percent away from the house.
This Old House explains that horizontal cracks are the most concerning, often tied to soil pressure or water pushing the wall inward, and that diagonal cracks can indicate parts of the foundation moving differently. These deserve an engineer’s opinion before any injection. Our hydraulic cement guide includes a triage table.
Signs you need an engineer first
- Cracks that grow, spread or appear suddenly.
- Horizontal or diagonal cracks together with other movement signs.
- Doors or windows that suddenly stick, or gaps that keep growing.
- Cracks wider than about 1/4 inch, or uneven floors or leaning walls.
- Water entering through the foundation.
- You are buying a home with foundation cracks. This Old House advises a structural engineer’s inspection before deciding.
What injection costs
Published sources give total repair ranges, not a reliable per-foot injection price. This Old House lists foundation crack repair from about $2,224 to about $8,134, with an average near $5,179, depending on the extent of movement, the cause and the repair type. Bob Vila gives a broader span, from under $50 for a hairline crack to more than $8,000 for a serious fix. Get at least three written quotes and ask each contractor to itemize the materials, number of cracks, length and any related drainage work. Our hiring guide explains how to verify licensing and compare bids.
Questions to ask a contractor
- Is this crack structural, leaking or cosmetic, and how did you decide?
- Why epoxy or why polyurethane for this crack?
- Has movement stopped? Will you monitor it?
- What will you do about the water source?
- What does the warranty cover and for how long?
- If the crack reopens, what happens?
DIY kits and their limits
Retail crack kits exist, and Bob Vila mentions that a DIY concrete crack repair kit can work for wider cracks, but also advises a professional inspection first in case the crack has a serious cause. If the crack is wet, wide, horizontal or growing, skip the kit and get it assessed. A DIY fix that hides a symptom can delay finding a real problem.
After the repair
- Mark the ends of the crack with a pencil and the date, then check it periodically.
- Fix grading, gutters and downspouts so less water reaches the wall. See our exterior drainage guide.
- Watch humidity in the basement. See basement humidity levels.
- If water appears again nearby, the system needs drainage, not just another injection. See our cost guide.
Related guides
How we put this guide together
This guide was drafted with AI assistance and then edited for the site against the public sources listed below. We are not engineers or contractors. The material comparison is limited to what Bob Vila and This Old House state; we do not make claims about product strength or lifespan. If you spot an error, use the contact page and we will correct it.
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