Not every crack is a problem
Concrete shrinks as it cures, and fine cracks in foundation walls and slabs are common and often harmless. The cracks that matter are the ones that let water in, that are widening over time, or that show movement: one side higher than the other, stair-step patterns in block walls, horizontal cracks in basement walls, or cracks wider than a credit card's thickness.
A simple way to track a crack is to mark its ends and width with a pencil and date, and photograph it with a ruler beside it. Check again over several months. A crack that grows needs attention.
Types of cracks
- Vertical hairline cracks in poured concrete walls are usually shrinkage cracks. If they leak, they can be sealed.
- Diagonal cracks often come from differential settlement, where one part of the foundation has moved more than another.
- Horizontal cracks in basement walls can mean soil pressure is pushing the wall inward. This is more serious and should be evaluated promptly.
- Stair-step cracks in block or brick walls follow mortar joints and often point to settlement or lateral pressure.
- Bowing or leaning walls are a structural concern.
Injection crack repair
For leaking or non-structural cracks in poured concrete walls, contractors commonly inject:
- Polyurethane, which expands and stays flexible, sealing against water in cracks that may move slightly.
- Epoxy, which bonds the concrete on both sides of the crack and can restore some structural strength in cracks that aren't actively moving.
The crack is cleaned, injection ports are attached, the surface is sealed, and the material is injected under pressure until it fills the crack through the wall's thickness.
Repairing bowing or cracked basement walls
When soil pressure is pushing a basement wall inward, sealing the crack isn't enough. Options include:
- Carbon fiber straps bonded to the wall to stop further inward movement.
- Steel beams or braces anchored at the floor and top of the wall.
- Wall anchors that tie the wall to plates buried in stable soil in the yard.
- Excavating and rebuilding severely damaged walls.
An engineer can help decide which approach suits your wall.
Address the cause
Water and soil pressure cause many foundation cracks. Improve drainage around the house, keep gutters and downspouts working, and grade soil away from the foundation. In basements, interior or exterior drainage systems and a sump pump may be needed to relieve water pressure.
Questions to ask
- Is this crack structural or cosmetic, and how can you tell?
- What material will you use, and why?
- Will this repair stop water, stop movement, or both?
- Should an engineer look at this?
- What's the warranty on the repair?
Cracks in brick and stone veneer
Cracks in brick or stone veneer often reflect movement in the foundation beneath. Repointing the mortar fixes the appearance but not the cause. Have the foundation evaluated first, then repair the veneer once movement has stopped.
Garage and patio slabs
Cracks in garage floors and patios are common and usually not structural, because those slabs aren't part of the house's foundation. Sealing them keeps water out and slows deterioration. Cracks that are offset, growing, or that connect to cracks in the house's foundation are worth having checked.
Timing
Injection repairs can be done in most weather, but some materials cure best within a certain temperature range. Ask the contractor about timing if you're scheduling in winter.