Kai Mallari's Notes'

Measure and Date Cracks Before Deciding Repair Is Needed (Home Systems)

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Measure and Date Cracks Before Deciding Repair Is Needed

idea decision-rule

Claim: The most important variable for any foundation crack is not current width but whether it is growing — so the first owner action is always to mark, measure, and date the crack, not to call a repair contractor.

Mechanism

A stable crack and a growing crack look identical in a single snapshot. The difference — which determines whether the crack is cosmetic or structural — only becomes visible over time. Marking crack ends with a pencil line (perpendicular to the crack) and writing the date beside each mark creates a temporal baseline. A photograph in consistent lighting creates a visual record.

The decision logic:

  • Crack stable over 6–12 months → cosmetic; no repair needed unless water is entering
  • Crack widening → active movement; escalate to structural engineer assessment
  • Crack that appeared suddenly → also escalate regardless of current width (sudden = active force)

Why this matters before calling a contractor: foundation repair contractors are not neutral advisers. Measuring and dating first lets you arrive at any consultation with actual data rather than impressions — and lets you distinguish a contractor who recommends repair from one who agrees the crack is stable.

Tools:

  • Pencil or permanent marker
  • Tape measure or crack-width gauge card (credit card = ~0.75 mm; business card = ~0.4 mm as rough comparators)
  • Phone camera
  • Avongard crack monitor (~60) for higher precision if the crack is near the engineer threshold — it overlays a millimetre grid and allows sub-millimetre measurement without re-measuring from scratch

The 6 mm (~¼ inch) threshold: this is the commonly cited width at which a vertical or diagonal crack moves from “monitor” to “engineer assessment.” Width is measured at the widest point. If you cannot close a credit card (0.75 mm) into the crack gap comfortably, you are at or below 1 mm. If a finger fits, you are well above 6 mm. For the gap between, a ruler or gauge card is the right tool.12

Scope

  • Applies to all crack types before they are categorised as horizontal (horizontal → engineer immediately, no monitoring stage needed)
  • Does not replace engineering assessment when the engineer threshold is met (>6 mm, offset, actively widening, or any horizontal crack)
  • The monitoring protocol applies to detached home foundations; strata common-property foundation work would involve the strata corporation

Idea Compass

North: Where this comes from

  • foundation (Home Systems) — the component note this idea supports
  • Basic engineering practice — temporal comparison is how you distinguish stable from active cracking

East: Tensions / failure

  • The temptation to call a contractor immediately — contractors observe the crack once; they cannot tell you if it is growing without a prior baseline
  • The temptation to ignore it entirely — a growing crack that is not monitored reaches the repair threshold without warning

South: Where this leads

West: What’s similar

  • Monitoring a water heater for the first signs of rust or pooling — the same “baseline + change detection” logic applied to a different component
  • How you monitor a car tyre for slow leaks — measuring and noting is more useful than a single snapshot

Sources

Footnotes

  1. This Old House — foundation cracks: marking ends and dating is recommended for tracking progression; “any crack that continues to grow in width or length isn’t normal” — https://www.thisoldhouse.com/foundations/foundation-cracks ↩

  2. InspectMT — 1/4 inch (6 mm) as the professional assessment threshold for crack width — https://inspectmt.com/post/diagnosing-foundation-cracks-identification-causes-and-solutions ↩

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