Concrete Crack Diagnosis Reference

Why this matters

Cracks in concrete are everywhere - driveways, garage floors, foundation walls, slabs. Most are cosmetic + harmless; a few are structural + serious. Service techs walk past cracks every day without knowing which is which. The one who can read them protects the customer + builds trust by flagging real problems (or reassuring on harmless ones). This is the field card.

Why concrete cracks at all

Concrete shrinks as it cures (water content reduces); thermal cycles expand + contract it; soil settles unevenly; water erodes the soil under it. Some cracking is inevitable - controlled crack joints (the visible scored lines in driveways + slabs) exist specifically to direct where the unavoidable crack goes.

The question isn't "is the concrete cracked?" The question is "is this crack signaling a structural problem, or is it normal shrinkage / expansion?"

Visual signatures + what they mean

Hairline crack, thin + uniform, runs through the slab: shrinkage crack from initial curing. Cosmetic. Common on driveways + garage floors.

Crack at a corner (re-entrant corner of an L-shape): stress concentration; very common. Mostly cosmetic.

Crack along a saw-cut control joint: working as designed. Sometimes worth filling for water exclusion but otherwise not concerning.

Wide crack (1/4" or more) with one side higher than the other (vertical offset): significant. Indicates soil movement / subsidence. Investigate.

Stair-step crack in foundation block wall: settlement OR lateral pressure (saturated soil pushing in). Common in block foundations + structural in many cases.

Horizontal crack in foundation wall: serious. Block walls can crack horizontally from soil pressure pushing in. Refer to structural engineer.

Crack with rust staining at edges: rebar inside has corroded + expanded; structural concern. Especially around pool decks, balconies, exposed concrete.

Map cracking / craze cracking (network of fine cracks): surface curing issue from initial pour. Cosmetic.

Crack opens + closes seasonally: thermal cycling. Watch over a year; if it stays predictable, it's environmental, not structural.

Crack widening over months / years: progressive. Structural concern. Foundation movement.

Measurement matters

For tracking changes:

• Photograph with a coin (or quarter, or ruler) for scale
• Mark the ends of the crack on the surface with pencil + date
• Re-photograph in 3 months, 6 months
• If the crack extends past the marks, it's actively progressing - refer

Stable cracks aren't urgent. Moving cracks are.

Common locations + their typical causes

Garage floor: shrinkage cracks at corners + along control joints normal. Wide cracks may indicate subsidence - check for door alignment issues, drainage near the slab.

Driveway: shrinkage + thermal. Tree roots underneath can lift sections. Repair if creating a trip hazard or water-pool issue.

Patio / walkway: similar to driveway. Settling near downspout = drainage issue (water eroding soil).

Basement floor: shrinkage cracks common + cosmetic. Wide cracks with displacement = slab movement, possibly from heaving (frost OR expansive soil) or settling.

Foundation wall (interior):

• Vertical hairline cracks: shrinkage; usually cosmetic. Seal with epoxy injection if water entry.
• Diagonal cracks from corners of openings: stress concentration; investigate if wide.
• Horizontal: serious (saturated soil pressure).
• Stair-step in block: settlement OR pressure; investigate.

Foundation wall (exterior): same patterns as interior + add weather + freeze-thaw cycles. Look for repeating freeze damage at the top of walls.

Pool deck: rust staining at cracks = rebar corrosion. Expensive to fully repair; surface repair as interim.

Doors + windows as movement indicators

When foundation moves, doors + windows get hard to operate. Customer report of "the front door sticks in summer + opens fine in winter" is foundation moving with seasonal moisture. Crack progression + door operation should correlate.

If a foundation is moving, the customer's whole interior shows it: drywall cracking at corners of door + window openings, baseboard gaps, floor sloping.

When to refer (structural engineer)

• Horizontal crack in foundation wall
• Stair-step crack widening over time
• Vertical offset > 1/4"
• Multiple cracks throughout foundation
• Customer reports doors/windows newly hard to operate
• Floor visibly out-of-level
• Cracks accompanied by water entry that resists waterproofing

Structural engineer evaluation costs money but protects the customer + you. Don't quote remediation of structural cracks without engineering - the wrong fix can make it worse.

When customer can DIY

Surface cracks in garage floors + driveways:

• Clean crack
• Apply concrete crack filler / sealant
• Cosmetic only; doesn't address underlying movement

Customer-level repair is fine for visible cosmetic concerns. Don't represent it as structural repair.

Foundation repair options (when warranted)

Hydraulic cement injection: fills hairline cracks; stops water entry.

Epoxy injection: structural-grade adhesive bonds two sides of crack; restores some integrity.

Carbon fiber straps: reinforce vertical OR diagonal cracks externally.

Steel beams + braces: stabilize bowing or shifting foundation walls.

Helical OR push piers: stabilize sinking foundation; transfer load to deeper soil OR bedrock.

Wall replacement / underpinning: severe cases.

Each requires assessment of cause + scope. Repair without addressing cause (drainage, soil) leads to recurrence.

Concrete vs other-trade interactions

Plumbers: slab leak in concrete floor can cause moisture-driven cracking nearby. Slab leak repair + crack monitoring after.

HVAC: condensation drip from refrigerant lines crossing slab can erode + crack concrete.

Roofers: gutters discharging at foundation can erode soil, cause settlement, crack walls.

Landscape: drainage modifications + grading affect foundation moisture.

Cross-trade observation is the value-add when you walk a job and see issues outside your scope.

Pool deck specifics

Pool decks crack from:

• Shrinkage during pour
• Thermal cycling
• Rebar corrosion from chlorinated water exposure
• Pool shell movement underneath

Pool deck repair is specialty work. Surface refinishing covers cosmetic; structural needs assessment.

Customer education

When you see a crack, you can:

• Document: photograph; note location + size
• Categorize: "shrinkage / cosmetic" vs "investigate further"
• Recommend: monitoring schedule, sealant for water exclusion, OR referral

Customers feel reassured by the categorization. They feel scared without it. The walk-through-with-cracks conversation builds trust.

What NOT to say

You are not the engineer, and the wrong sentence in a driveway conversation creates liability for your company and panic for the customer.

"Your foundation is failing." You do not know that from a visual walk-by, and the customer will repeat it to a realtor, an insurer, or a buyer. Say what you saw and what it may indicate, then recommend the evaluation.

"That's nothing, don't worry about it." Dismissing a crack you have not measured is the mirror-image error. If it turns out to be progressive, you owned the reassurance. Say it looks consistent with shrinkage, and give them the monitoring method.

"This house is going to need underpinning / piers." That is an engineer's call and a specialty contractor's scope. Naming a repair method commits your company to a diagnosis you are not licensed to make.

"The builder did this wrong." Even when it looks true, you are speculating about work you did not see performed. It invites the customer into a dispute and can pull you into it as a witness.

"It's mold." Staining, efflorescence, and mineral deposit around a crack look alike. Efflorescence is salt left by evaporating water and wipes off dry. Do not name a health hazard you have not tested for.

Any number you did not measure. "About a quarter inch" from six feet away is how a hairline becomes a structural claim. Measure it or describe it without a number.

"I can fill that for you" on a crack that is still moving. Sealing an active crack hides the movement and guarantees a callback when it re-opens through your patch.

What to say instead: describe the crack (location, width measured, offset or none, direction, staining), place it in a category (consistent with shrinkage, or worth investigating), give the monitoring plan with dates, and name who evaluates it if it moves. Put the same thing in the ticket. Confident, specific, and inside your lane is what earns the referral.

References

• ACI 224 (Cracking in Concrete)
• ASTM C1543 (cracking measurement)
• Foundation Performance Association resources
• ICC + IRC foundation requirements
• Manuall internal: Common Building Materials, Mortar + Grout Selection