Note about foundation cracks: Generally speaking for concrete, stone, brick and masonry block foundation walls and cement floors, hairline cracks and cracks less than 1.5 mm wide or the thickness of a penny are fairly common and usually do not warrant any corrective action. Most of these small tight cracks are caused from normal settlement of the structure which usually occurs within the first few years after construction. Cracks that are larger than 1.5 mm should be sealed with cement paint, caulk or mortar to prevent water from getting in and will help in monitoring. Be aware that flexible caulks should not be used to fill cracks you want to monitor, flexible caulk stretches and will not show continued movement.
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. Non-shrinking grout is a good choice. If a foundation crack is leaking water you’ll want to seal it, not just monitor it.
“All” cracks, even hairline cracks should be monitored for continued movement.
If a crack has been sealed or filled in with paint, caulk or mortar and you notice it has re-cracked or the crack has opened up or gotten larger (and is not shrinkage of the filler product) there is movement and reason some concern even if very little. When continued movement is observed in foundation cracks they should be evaluated as there may need corrective action. Large cracks, 6.5 mm or 1/4 inch and greater after they are sealed, should be carefully watched to ensure there is no continued 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.
Examination of Cracks
A. Examine the nature and severity of the crack:
1. What direction are the cracks going and where are
they the widest?
2. Note sloped floors, bulging walls and doors that do
not fit.
B. Determine the probable cause:
1. Foundation erosion.
2. Decay and/or improper use of materials.
3. Structural failure.
4. Change in materials or geometry.
5. Changes in moisture content.
6. Thermal changes:
a. Horizontal or diagonal cracks near the ground
at piers in long walls: due to horizontal
shearing stresses between the upper wall and
the wall where it enters the ground,
b. Vertical cracks near the ends of walls,
c. Vertical cracks near the top and ends of the
facade,
d. Cracks around stone sills or lintels: due to
expansion of the masonry against both ends of
the tight fitting stone piece that cannot be
compressed.
How to Monitor Foundation Cracks – Three Simple Methods
A. Simple Method of Monitoring Cracks Using Tape and Pencil:
- Place a high quality sticky piece of tape on each side of the crack.
- Draw one short line on each piece of tape at convenient distance apart (2 inches) and parallel to the crack. Use a ruler to measure as exact as possible or use something as a template for multiple marking.
- If there is movement in the crack, the distance between the line on the tape will vary; If the crack is long, several monitors will be needed.
- Make a record chart of the distance between the marks of the tape at weekly intervals.
- Keep accurate records of these measurements and place them along with photographs in file.
- If significant widening occurs, report this with back-up data and copies of photographs to a structural engineer for consultation.
B. Monitoring Cracks Using Glass and Epoxy:
- Take a small piece of single strength window glass a microscope slide is good) to bridge over the crack. Tiny glass rods are also made for this purpose.
- Epoxy the ends of the glass to the masonry on either side of the crack; locate it in an inconspicuous place.
- If the glass breaks, it is an indication that the walls are still moving and that the crack is widening.
C. Monitoring Cracks Using the Avongard Crack Monitor:
The Avongard Crack Monitor is a simple and effective gauge to measure the movement of cracks in brick, concrete, or masonry structures. 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. For more Info./Order here: http://www.avongard.com/
- Position the monitor over the crack with the vertical “0” line on scale parallel with the crack to be measured.
- Fix the monitor with screws or adhesive.
- Cut the transparent tape holding the two plates of the scale on the monitor in a fixed position with a sharp knife; over time, the degree of movement on either side of the crack will be measured as the two plates slide independently of one another.
A Crack Progress Chart is included with each Avongard Monitor to provide an accurate record of crack movement. Just check the gauge at regular intervals and copy the position of the cross hairs onto one of the grids on the chart. Once you’ve established a pattern of movement on the Progress Chart, an engineer can then decide what remedial action is needed.
