Foundation crack movement monitoring devices & methods:

This document describes how foundation or slab cracks can be monitored for evidence of movement and what general advice makes sense for building owners or buyers where foundation damage is found and/or where further foundation inspection, testing, diagnosis, or repair appear warranted based on a general field inspection.

We include discussion of methods used to perform ongoing monitoring of building foundations for cracking and movement.

Methods for Monitoring Foundations for Evidence of Ongoing or Episodic Movement

Building foundations may be moving, either continuously or episodically. Most movement is episodic, that is, the movement is not a simple and continuous creep but rather foundation movement or cracking occurs in fits and starts.

Our sketch (left) shows a bulged masonry block foundation wall that has bowed in two inches at its innermost point.)

Usually foundation movement and further cracking occurs in response to occurrences of what has caused the cracking in the first place.

See FOUNDATION DAMAGE SEVERITY and

then FOUNDATION MOVEMENT ACTIVE vs. STATIC for distinguishing severe and also ongoing foundation movements.

Examples of Causes of Ongoing Foundation Damage/Movement

• Continuous vehicle traffic too close to the foundation (weight) or even in a nearby roadway (vibration)
• Continuous blasting and nearby site work
• Continuous overloading or point loading on the foundation due to construction or building design

On occasion a foundation cracked or damaged by an event (drove a heavy vehicle too close to the masonry block foundation wall) may later move, crack or bend, buckle, lean, bulge, etc. in response to other site conditions that it was previously able to resist before it was weakened by the original damage (frost, water, other vehicles).

Examples of Episodic or Discontinuous Causes of Foundation Damage/Movement

• Seasonal area flooding of surface water or subsurface groundwater
• Seasonal freezing weather - frost heaving and frost lensing

List of Simple Methods to Monitor a Masonry Foundation for Evidence of New or Ongoing Movement

• Crack Pins to monitor masonry structure movement:
  
  a metal pin is secured to the masonry surface on either side of the crack. Periodic measurements are made of the distance between the two points of the pins.
  

• Crack monitor slide devices:
  
  such as a glass slide, (shown above) a more complex set of moving glass slides that include fine markings can be epoxied (or mechanically fastened) acros
  
  s a building foundation crack.
  
  Masonry crack monitoring devices provide accurate indication of any additional movement in the foundation wall. Beware: small amounts of foundation movement occur in masonry materials as a normal effect of temperature and moisture changes and may be typicallyi a millimeter or so. Don't mistake these causes for ongoing building movement. (Photo above courtesy of Avongard.)

Photo atbove of a crack monitor installed in place is courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].)

• The Avongard CRACK MONITORING DEVICE, [Image] a $16.00 U.S. device measuring 1.25" x 5.75", is an example of this product.
  
  "The Avongard Crack Monitor consists of two overlapping acrylic plates. One plate is white with a black millimeter grid, while the other is transparent with red cross hairs centered over the grid.
  
  Once the Crack Monitor is in position across a crack, the cross hairs shift vertically or horizontally on the grid if movement occurs,so that anyone can easily see and track crack movement."
  
  The Avongard crack monitor can identify masonry wall movements down to 0.5mm and can handle total movement of 30.75" in crack width and 0.375" upwards movement (one side of the surface lifting or protruding past the other, such as on a concrete floor).
  
  For longer term monitoring of a cracked masonry wall or floor we like this device. The monitor can also be used to measure movements in foundation corners by incorporating an angle bracket. Avongard provides a movement progress chart that permits logging of observations over time.
• Masonry Crack Fillers:
  
  if a horizontal, vertical, or diagonal masonry crack is filled with hard masonry patching compound, any substantial future movement is likely to show up as a new crack in the patched area (or nearby). Beware: some masonry products shrink when they dry and cure - don't mistake a patch shrinkage crack for building movement.
  
  But if a foundation crack is leaking you'll want to seal it, not just monitor it.
• Masonry Crack Caulks:
  
  filling a foundation crack with a masonry caulk is a quick, inexpensive, and effective way to seal the crack; some caulks, such as pourable sealant used to close floor cracks during radon mitigation work, are easy and effective to use.
  
  Watch out: flexible materials such as common caulks or sealants won't show small amounts of future building movement.

• Measure and Document Foundation Movement:
  
  masonry foundation cracks alone may not be the only nor even the most critical evidence of foundation movement.
  
  If a foundation wall is leaning, bending, or bowing, that stress may have resulted in several small width cracks that do not adequately describe the total amount of foundation movement.
  
  A written and photo inventory of foundation cracks, simple measurement of foundation crack length and width as well as documenting their location, may be combined with simple measurements of the total lean or bulge in a foundation wall.
  
  Photo of an inspector measuring the width of a step rack in this brick veneer wall is provifded courtesy Carson Dunlop Associates, Toronto, Ontario.
  
  See FOUNDATION BULGE or LEAN MEASUREMENTS for details.
• A foundation inspection & diagnostic report:
  
  a thoughtful inspection of the building and site as well as an inventory of existing cracks permits a diagnosis of the causes of foundation damage as well as its extent.
  
  If there is evidence of significant foundation movement, we recommend that you take this more costly step.
  
  See FOUNDATION CRACK DICTIONARY for guidance.
• Other foundation movement monitoring devices
  
   are used by professional engineers, including load cells or pressure cells, extensometers used with a borehole and tape, tilt meters that measure angular change or lean, strain meters, beam sensors, and soil movement sensors.
• Companies such as Slope Indicator sell these and other sensing and measuring devices.
• U.S. GSA, MONITORING AND EVALUATING CRACKS IN MASONRY [PDF] (2016) Retrieved 2020/12/14
  
  Excerpts:
  
  This standard includes guidance on monitoring and evaluating cracks in masonry. Three different methods are described and include the following:
  
  Using tape and a pencil, Using glass and epoxy, and Using the Avongard Crack Monitor.
  
  Cracks in masonry are evidence that the building material has moved or is still moving, (active cracking).
  
  Some causes of cracking include: settlement or foundation erosion, decay of materials, "vandalism" by renovators, structural failure, change in materials or geometry, and moisture and temperature changes.
  
  In foundation piers and piles, general cracking is often due to settlement or rotation of the pier footing.
  
  Vertical cracking or bulging of a masonry foundation wall is often due to physical deterioration of the pier from exposure, poor construction or overstressing.
  
  Horizontal cracking or bowing of a masonry foundation wall may be caused by improper backfilling, or by swelling or freezing and heaving of water saturated soils adjacent to the wall.
  
  Differential settlement of a masonry foundation wall may be caused by many different things including soil consolidation, soil shrinkage, soil swelling, soil heaving, soil erosion or soil compaction.
  
  Differential settlement of a chimney is often caused by inadequate foundations which may cause the chimney to lean and crack.

...

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• FOUNDATION SHRINKAGE vs EXPANSION vs SETTLEMENT

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