Brick Veneer Crack Monitor Installation

Why this matters

A diagonal crack in brick veneer above a door or window is the most common diagnostic symptom a foundation contractor sees. The homeowner asks: is this getting worse? The contractor needs to answer with data, not gut feel, because the answer drives whether the next call is a structural assessment, a remediation quote, or a "the crack is stable, no action needed" closeout. The crack monitor (also called telltale, crack gauge, or movement monitor) is the cheapest, most defensible tool for that answer. Installed correctly, it measures crack movement to 1 mm precision over months. Installed wrong, it gives misleading readings and the contractor ends up either over-quoting unnecessary work or under-quoting a problem that goes catastrophic. The technique is simple; the discipline is in the protocol.

What a crack monitor measures

A crack monitor is a two-piece device, one piece anchored on each side of a crack. The two pieces overlap with a precision grid; as the crack opens, closes, or shears, the grid shifts and the new alignment reads directly in millimeters.

Three monitor types are common:

Avongard Standard Telltale: cross-grid plastic monitor, measures horizontal and vertical movement in 1 mm increments. The most-used model in residential structural monitoring. Range: 20 mm in each direction.

Avongard Corner Telltale: same principle, configured to monitor at 90-degree corners (interior or exterior).

Digital crack monitor (Geokon, Roctest): electronic readout, logging capability, sub-millimeter resolution. Used in commercial or litigation-grade monitoring.

For typical residential brick veneer diagnostics, the Avongard Standard telltale is the right tool. Cheap, simple, glassy-clear plastic that survives weather, easy to photograph.

When to install a monitor

Install monitors when:

Crack cause is uncertain. New crack discovered; could be active movement or aged settling.

Crack is in a location where movement matters. Above a door/window opening, at a corner of the building, at a foundation-to-veneer interface.

The homeowner is considering remediation but wants to see if the crack is stable before spending money.

Litigation or insurance documentation is needed. The monitor with date-stamped photos becomes evidence.

Time-budget for monitoring exists. Useful readings require minimum 3 months of observation; ideally a full year covering all seasons (wet, dry, freeze, thaw).

Do NOT install a monitor when:

Crack is obviously catastrophic (greater than 1/4 inch wide, mortar joint failure, visible structural displacement). Skip to engineering assessment; the monitor is not adding decision value.

Active leaking through the crack is visible (water staining, salt deposits, vegetation growing in the crack). The water itself is the diagnostic.

Homeowner wants immediate action. Monitoring takes months. If the homeowner needs an answer in two weeks, hire an engineer for a single-visit assessment instead.

Choosing monitor locations

Walk the building exterior and interior. Identify cracks by:

Direction: vertical, diagonal, stair-step through mortar joints, horizontal.

Width: hairline (under 1/32 inch), thin (1/32 to 1/8 inch), wide (over 1/8 inch).

Location: above/below openings, at corners, at the foundation line.

Pattern: single crack vs systematic pattern (multiple parallel cracks suggest racking; multiple radiating cracks suggest a point of settlement).

Install monitors at the cracks that will tell you the most:

The widest crack (most active).

A crack near a corner of the building (where settlement of one footing will show first).

A crack above the largest opening (door or large window; openings concentrate stress and reveal movement early).

A crack at a foundation-to-veneer interface (separation between rigid foundation and flexible veneer indicates relative movement).

For a typical residential job with multiple cracks, install 2 to 4 monitors at strategic locations rather than one per crack.

Surface preparation

The monitor adheres to the substrate. Adhesion failure invalidates the reading. Three substrate types in brick veneer:

Brick face: clean, dust-free, dry. Wire brush any loose paint, efflorescence, or surface contamination. Wipe with denatured alcohol; allow to dry.

Mortar joint: similar prep. Mortar provides slightly less reliable adhesion than brick face; preference is to anchor monitor pieces to brick faces on each side of the crack.

Painted brick: scrape any loose paint flakes. The monitor adheres to the paint surface; if the paint is sound, adhesion is acceptable. Inform the homeowner that monitor removal will leave a paint mark.

Stone veneer: clean as for brick. Smooth stone faces give better adhesion than rough rubble stone; on rough stone, find the flattest available surface near the crack.

Installation

Step 1: Mark the alignment. Position the monitor across the crack as it will be installed. Mark the four corner positions on the substrate with pencil or chalk. The monitor must be square to the crack (one axis of the grid parallel to the crack) for accurate movement reading.

Step 2: Mix the adhesive. Most installations use a two-part epoxy (Loctite 5-Minute Epoxy, Devcon 5 Minute Epoxy, or a structural-grade methyl methacrylate). Pre-mix small batches; do not mix more than will be used in 3 to 5 minutes of working time.

Step 3: Apply adhesive to the monitor backside. A small bead at each of the four corners of each monitor piece is sufficient. Avoid adhesive in the middle of the monitor (would interfere with monitor flexibility under movement).

Step 4: Position the monitor. Place the two pieces in their pre-marked positions. The grid pattern should align at the zero reference point: the cursor on one piece centered over the zero on the other piece's grid.

Step 5: Hold for cure. Tape the monitor in place with painter's tape if 5-minute epoxy is used; hold for 5 to 10 minutes minimum. Verify alignment before tape removal.

Step 6: Document the initial state. Photograph the monitor with a ruler in frame for scale, the date written on a piece of tape adjacent to the monitor, and the location of the monitor on the building (wide shot showing the monitor in context). The initial reading is the zero datum.

The reading protocol

Installation is the easy half. The monitor produces no decision value at all unless the readings are taken on a schedule and recorded the same way every time.

Read on a fixed interval, monthly, and additionally after any event that could plausibly move the building: a heavy sustained rain, the first hard freeze, a drought break, excavation or heavy equipment on the property, a plumbing leak repair. A reading taken because something happened is worth more than a reading taken because it was Tuesday, but the routine monthly reading is what makes the event reading interpretable.

Record four things at every visit, in the same order, on the same form: the date, the horizontal reading in millimetres, the vertical reading in millimetres, and a photograph of the monitor taken square-on with the scale legible. Add the weather and the recent weather, because the whole point of a year of monitoring is to separate seasonal movement from progressive movement, and you cannot do that without knowing what the ground was doing.

Read the grid the same way every time. Note which piece carries the cursor and which carries the scale, and record the reading as a signed change from the zero datum rather than as a raw grid position. Opening is positive, closing is negative, and shear shows up as movement on the axis parallel to the crack.

Never take a reading from memory or from the previous form. Read the monitor, then compare.

Interpreting the record

The record answers one question: is the movement cyclic or progressive.

Cyclic movement returns to the datum. The crack opens through one season and closes back through the next, and after a full year the reading is at or near where it started. That signature points at seasonal soil moisture change, thermal movement, or both, and it means the structure is moving within a range it has been moving within for some time. The finding is that the crack is active but not progressing.

Progressive movement does not return. Each seasonal cycle ends further from the datum than the one before, or the reading walks steadily in one direction regardless of season. That is the finding that changes the recommendation, and it does not need a threshold in millimetres to be actionable: a crack that has not come back to datum after a full seasonal cycle is a crack that is going somewhere.

A flat record over three months is not evidence of a stable building. It is evidence of three months. Say so in exactly those terms to a homeowner who wants to close the file early, and finish the year.

Escalate to a structural engineer before the monitoring period ends, not after, if the reading accelerates between two consecutive intervals, if a new crack appears while an existing one is being monitored, if any monitor shows shear (movement along the crack rather than across it), or if the crack widens past the point where the article's own do-not-install thresholds would have sent it to an engineer in the first place. Monitoring is a diagnostic, not a holding pattern.

Removing the monitor

At the end of the period, photograph the final state, then remove the monitor with a putty knife and record the reason for removal (period complete, escalated to engineering, remediation scheduled). Warn the homeowner in advance that removal leaves an epoxy footprint and, on painted brick, a paint mark. Leave the record with the homeowner as well as in the job file; it is theirs, and it is what the next contractor or the next insurer will ask for.

References

• IRC 2021 Section R403 Foundations (referenced for foundation design and movement context)
• ACI 224R Control of Cracking in Concrete Structures (referenced for crack interpretation in structural contexts)
• Avongard Technical Data Sheets for Standard Telltale and Corner Telltale current edition
• US Army Corps of Engineers EM 1110-2-1908 Instrumentation of Embankment Dams and Levees (crack monitoring methodology, transferable to building contexts)