Foundation Crack Monitoring: How to Track If Cracks Grow
Monitoring makes sense for cracks where you are unsure whether they are cosmetic or structural. Obvious structural cracks like horizontal cracks with visible wall bowing should be evaluated by a professional immediately rather than monitored. But vertical cracks, thin diagonal cracks, and hairline cracks of uncertain origin benefit from a monitoring period that reveals whether the crack is in motion or has settled into its permanent state.
Document the Crack
Start by creating a thorough record of the crack's current condition. Take photographs of the entire crack from end to end, including close-up images with a ruler, coin, or other common object for scale. The scale reference allows you to compare photos taken months apart and detect changes that might not be obvious without a size reference.
Mark both endpoints of the crack with a pencil or fine-point marker. Draw a short line across the crack at each end, perpendicular to the crack direction, and write the date next to each mark. If the crack grows longer, it will extend beyond your endpoint marks, making the growth immediately visible without any measurement tools.
Record the crack's location on a simple sketch of the wall, noting which wall it is on, its height from the floor, its orientation (vertical, horizontal, diagonal), and any nearby features like windows, doors, pipes, or construction joints. This documentation becomes valuable context if you later show the crack to a contractor or structural engineer.
Measure Initial Width
Measure the crack width at three to four points along its length. Choose points that are evenly spaced and include the widest visible point. Mark each measurement location with a small numbered pencil mark so you can return to the exact same spot for future measurements.
A crack width comparison card is the most practical measurement tool for homeowners. These cards have printed lines of graduated widths, typically from 0.004 inches to 0.250 inches, that you hold against the crack to find the matching width. You can purchase them online for $5 to $15, or print free versions from structural engineering resources. A digital caliper provides more precise readings if you have one available.
Record each measurement with its numbered location and the date. Also note the approximate temperature, as concrete expands and contracts with temperature changes and this can cause small cyclical width variations that are not structural movement.
Install Crack Monitors (Optional but Recommended)
Crack monitors are inexpensive devices that provide continuous, easy-to-read tracking of crack movement. The standard type consists of two overlapping acrylic plates, one mounted on each side of the crack, with a calibrated grid printed on one plate and a crosshair on the other. As the crack moves, the plates shift relative to each other, and the crosshair's position on the grid indicates the direction and magnitude of movement.
Install the monitor across the widest point of the crack or at the location where you most want to detect movement. The plates are attached to the wall with screws, adhesive, or epoxy, one plate on each side of the crack. Position the monitor so the calibrated grid is visible and easy to read, and record the initial position of the crosshair on the grid.
Better crack monitors measure movement in two directions: across the crack (opening/closing) and along the crack (shear/sliding). This two-axis measurement reveals not just whether the crack is widening but whether the wall sections on either side are shifting vertically relative to each other, which indicates structural shear movement.
Crack monitors are available from construction supply retailers and online for $10 to $30 each. For most homes, one or two monitors on the most concerning cracks is sufficient. Engineering-grade electronic crack monitors that log data continuously cost $200 to $500 and are used for professional monitoring programs.
Take Monthly Measurements
Check each measurement point and crack monitor monthly, ideally on the same date each month to keep intervals consistent. Record the crack width at each numbered location, the position of the crosshair on any installed monitors, and the approximate outdoor temperature. Take a new photograph of the crack with a scale reference to maintain a visual record alongside the numerical data.
Continue monthly measurements for a minimum of six months. Ideally, monitor through a full seasonal cycle of twelve months that includes summer heat, fall cooling, winter cold, and spring warming. Concrete expands and contracts with temperature, so a crack may narrow slightly in summer and widen slightly in winter without any structural movement occurring. Only by measuring through a complete cycle can you distinguish normal thermal variation from genuine structural growth.
If at any point during monitoring the crack shows sudden, dramatic widening of 1/8 inch or more, or new cracks appear nearby, or you notice other signs of foundation distress like sticking doors or new interior wall cracks, stop monitoring and contact a structural engineer immediately. Sudden changes indicate active movement that should be evaluated before it progresses further.
Analyze the Data and Decide
After six to twelve months, review your measurements for patterns. Plot the width measurements on a simple graph with dates on the horizontal axis and widths on the vertical axis. The trend line tells the story.
Flat line with minor fluctuation: The crack is stable. Width measurements that stay within 1/32 inch of each other, with any variation correlating to temperature changes, indicate a crack that has reached its final state. This crack can be repaired at your convenience, and the repair is highly likely to be permanent because the forces that created the crack are no longer active.
Gradually increasing line: The crack is actively growing. Width measurements that show a consistent upward trend, even if the increase is small, indicate ongoing forces acting on the foundation. This crack needs professional evaluation to identify the cause and determine the appropriate repair. Simply injecting a growing crack will result in the repair failing as the crack continues to widen.
Seasonal oscillation without upward trend: The crack is responding to thermal cycles but is not structurally growing. This pattern shows the crack widening in cold months and narrowing in warm months, returning to approximately the same width each cycle. This is normal concrete behavior and not a structural concern. A flexible polyurethane injection is a good repair choice for these cracks because it can accommodate the seasonal movement.
Six to twelve months of monthly measurements reliably distinguishes stable cracks from active ones. Use pencil marks and a crack width card for basic monitoring, or install $10 to $30 crack monitors for precise, continuous tracking. Stable cracks can be repaired at your convenience. Growing cracks need professional evaluation before repair.