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

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