Monitoring And Evaluating Cracks In Masonry
- Procedure code:
- HSPG Prepared For NPS - Southeast Regional Office
- Unit Masonry
- Last Modified:
MONITORING AND EVALUATING CRACKS IN MASONRY
A. This standard includes guidance on monitoring and
evaluating cracks in masonry. Three different methods
are described and include the following:
1. Using tape and a pencil,
2. Using glass and epoxy, and
3. Using the Avongard Crack Monitor.
B. Cracks in masonry are evidence that the building material
has moved or is still moving, (active cracking).
C. 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.
1. In foundation piers and piles, general cracking is
often due to settlement or rotation of the pier
2. Vertical cracking or bulging of a masonry
foundation wall is often due to physical
deterioration of the pier from exposure, poor
construction or overstressing.
3. 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.
4. 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
5. Differential settlement of a chimney is often
caused by inadequate foundations which may cause
the chimney to lean and crack.
D. See 01100-07-S for general project guidelines to be
reviewed along with this procedure. These guidelines
cover the following sections:
1. Safety Precautions
2. Historic Structures Precautions
4. Quality Assurance
5. Delivery, Storage and Handling
6. Project/Site Conditions
7. Sequencing and Scheduling
8. General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing
this procedure and should be followed, when applicable,
along with recommendations from the Regional Historic
Preservation Officer (RHPO).
A. Crack Monitor: Avongard, http://www.avongard.com/
A. A pencil, tape, ruler
B. Small piece of window glass (single thickness) or glass
C. Epoxy adhesive
D. Crack monitor
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
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
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
3.02 ERECTION, INSTALLATION, APPLICATION
A. Monitoring Cracks Using Tape and Pencil:
1. Place a piece of tape on each side of the crack.
2. Draw one short line on each piece of tape at a
convenient distance apart (2 inches) and parallel
to the crack.
3. 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.
4. Make a record chart of the distance between the
marks of the tape at weekly intervals.
5. Keep accurate records of these measurements and
place them along with photographs in file.
6. If significant widening occurs, report this with
back-up data and copies of photographs to the RHPO
B. Monitoring Cracks Using Glass and Epoxy:
1. 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
2. Epoxy the ends of the glass to the masonry on
either side of the crack; locate it in an
3. If the glass breaks, it is an indication that the
walls are still moving and that the crack is
C. Monitoring Cracks Using the Avongard Crack Monitor:
1. Position the monitor over the crack with the
vertical "0" line on scale parallel with the crack
to be measured.
2. Fix the monitor with screws or adhesive.
3. 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.
END OF SECTION