Concrete cracks. It shrinks as it cures, it expands and contracts with temperature, and houses settle a little in their first years. That is why a hairline crack is usually the least worrying thing a homeowner finds. The ones to take seriously are cracks that change, cracks that let in water, and cracks that come with doors sticking or floors sloping.
Reading the crack
| What you see | Often means | Next step |
|---|---|---|
| Thin vertical hairline in poured concrete | Curing shrinkage | Monitor; seal if damp |
| Horizontal crack along a block wall | Pressure from the soil outside, possibly water | Get it inspected |
| Stair-step crack through mortar in brick or block | Uneven movement of the wall | Get it inspected |
| Diagonal crack from a window or door corner | Differential movement, or just a stress point | Measure and monitor; inspect if growing |
| Crack plus sticking door or sloping floor | Movement somewhere in the structure | Inspect |
| Crack leaking water or showing efflorescence | Water getting in | Fix drainage, then repair |
Nothing here is definitive. These are lookalikes that a trained eye sorts out. Signs of foundation problems covers the full list, including the signs that are not foundation-related.
How to track a crack
- Mark the ends with a pencil and write the date.
- Photograph it with a coin or ruler for scale.
- Re-check after heavy rain and again after a dry spell.
- If it moves, grows or leaks, call for an inspection.
Mecklenburg County has been through serious drought recently and in past decades. Drought can dry and shrink some soils, and the NC Geological Survey lists foundation cracks and uneven floors among the results of shrink-swell soil movement. That is general background. Mecklenburg County’s soils vary lot to lot, from low to very high shrink-swell ratings in the county survey, so a crack is not proof that soil is the cause. The Charlotte soil guide explains the county picture.
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How cracks are repaired
- Surface patch or sealant. Fine for hairline cracks, and cheap. It doesn’t change why the crack formed.
- Injection. A resin or polyurethane filler is injected into the crack from the inside to seal against water and bond the concrete. It’s usually water control rather than a structural fix.
- Reinforcing a wall. Steel straps, carbon fiber or braces for walls that are bowing or cracking under soil pressure.
- Fixing the cause. Gutters, grading or drainage, and where the footing has moved, piers or underpinning. HomeGuide puts underpinning at $10,000–$30,000+.
The first two are surface or sealing work. The last two can be structural. Structural repair needs a permit; the contractor pulls it.
What it costs
HomeGuide lists minor crack repair at $250–$800 nationally, while settling, sinking or bowed-wall repairs run $4,500–$20,000. Charlotte sources disagree on the broader job: Angi’s Charlotte page gives $2,873-$12,299 for foundation repair, and Homeyou gives $2,987-$5,194 based on a modeled house. The difference is mostly scope. See foundation repair cost for how to read the spread.
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Cracks in different places
- Poured foundation wall or slab edge. Vertical hairlines are common. Diagonal cracks that widen toward the top or bottom suggest one end of the wall has moved more than the other.
- Block walls and piers. Horizontal cracks, or cracks that follow mortar joints in a stair-step, are more often tied to soil pressure or settlement than to curing.
- Brick veneer above the foundation. Brick can crack from a small movement and show it plainly. Stair-step cracks that run up from a corner are worth a look, especially if they have widened since you first noticed them.
- Crawl space walls and piers. Look at the piers holding the girder as well as the perimeter wall. A cracked, leaning or crumbling pier is a support problem, and it shows up as a sag above. See sagging floors over a crawl space.
- Garage and porch slabs. Slabs crack to relieve stress and often matter less than a wall crack, unless one side has dropped.
Where the house sits in time
Charlotte’s housing stock is fairly new: the Census puts the median home as built in 1995, and 43% of units date from this century. Newer concrete is still in its settling years, and older houses have more time for water, roots and drainage changes to have worked on the foundation. Age alone doesn’t tell you whether a crack matters. It is context for the inspection, and it helps explain why two nearby houses can behave differently. Angi also notes basements are rare in Charlotte, and slabs are popular.
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What to tell the contractor when you call
- When you first noticed the crack and whether it has changed.
- Where it is, inside or out, and which direction it runs.
- Whether doors, windows or floors have started to stick or slope.
- Any recent plumbing leaks, tree removal, regrading or heavy rain.
- Whether a seller’s disclosure or previous inspection mentioned the foundation. North Carolina’s disclosure form asks about foundation defects.
Those answers help the contractor decide what to measure and whether a full inspection is needed or a simpler fix will do.
Water and cracks
Water is behind more crack complaints than movement is. A crack that leaks after rain, or leaves white mineral deposits, is telling you water reaches the wall. The fix often starts outside: gutters that overflow, downspouts that empty beside the wall, soil that slopes toward the house. EPA’s mold guidance recommends grading the ground to slope away from the foundation so water does not collect around it. Sealing a crack from inside while water keeps arriving outside tends to move the problem. If the wall also looks bowed or the crack runs wide, it moves from drainage into foundation repair.
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When to call right away
- A crack that grows noticeably over days or weeks.
- A wall that bows inward, or a corner that has separated.
- Water coming through a crack during or after rain.
- New cracks that appear together with sticking doors, windows that will not close, or a sloping floor.
Those are not emergencies in the sense of a gas leak, but they are the cases where waiting a season makes the repair larger. The rest can be watched.
Before you sign
- Ask whether the quote is to seal a crack or to correct what is causing it.
- Get at least three written estimates from different contractors.
- Ask what the contractor will do if the crack reopens, and get the answer in writing.
- Be wary of anyone who calls a hairline crack an emergency to sign today.
Want a contractor to look at it? Call to schedule an inspection.