MASONRY WALL
Infrared
Analysis
Long Branch H.S.
Investigation: 7/95
Table
of Contents
Abstract
Evaluation
Illustrations
ABSTRACT
The purpose of the
infrared masonry wall survey is to utilize thermal
imaging techniques to isolate areas within the wall where
moisture has infiltrated. Only select elevations were
scanned on the night of July 12, 1995. These areas can be
seen in the Illustrations Section of this report.
The basic tool of
ABACUS Infrared Wall Survey is the Agema Thermovision 450
Infrared Thermal Measurement and Imaging System, using
the state of the art Electro-optical scanning mechanism,
the new SPRITE infrared detector, video interface and
control electronics and microprocessors for video output.
The infrared camera converts electromagnetic thermal
energy radiated from an object into electronic video
signals. These signals are amplified and transmitted to
the video processing part of the camera where the signals
are further amplified and the resultant image is
displayed on the viewfinder. The camera senses the
intensity of thermal radiation from the object surface,
and displays a monochrome image whose density corresponds
to the radiation intensity. The radiant energy levels are
interpreted as surface temperatures.
The same infrared
equipment utilized for roof moisture surveys is used for
masonry wall evaluations, however, the thermal dynamics
are very different. On roof surveys, moisture within the
roof system appears warmer than dry roofing components,
when scanned at night, because of solar energy retention.
Moisture within the masonry walls appears cooler than
sound, dry masonry because of evaporative cooling (when
scanned at night) due to infiltration.
The client selected
wall elevations were scheduled to be scanned on July 12.
A cooperative effort with local fire department allowed
the walls to be soaked prior to the survey. This wetting
of the walls provided the catalyst for moisture related
thermal differentials necessary for infrared thermal
imagery.
Wetting the walls
prior to the survey is for the purpose of creating a
thermal profile on the masonry surface. This procedure
would provide distinct heat patterns that would be
associated with a non-uniform substrate. The wetting
procedure consisted of allowing the water to soak the
exterior walls, and waiting a predetermined period of
time before scanning in order to allow most of the
surface moisture to evaporate, leaving only subsurface
moisture within the walls, which subsequently create the
thermal images. By utilizing the firehoses to wet the
walls, all contracted surfaces were heavily saturated
providing full moisture coverage of all wall surfaces.
Once the surface of the walls have dried, the infrared
survey commenced.
Scanning at night
allows for sufficient cooling of the masonry surfaces and
eliminates solar reflection. Solar reflection and
increased surface temperatures can distort or eliminate
the minute thermal changes being looked for during the
survey.
Because a crack in
the masonry wall will absorb more water than solid
masonry, it has a reservoir of coolant (water) trapped
behind it. As the residual water stored behind a crack
continues to evaporate, it cools the surface in the
immediate vicinity of the opening. These "cool"
spots are quite visible to the infrared camera.
Upon request,
certain portions of the thermal information obtained
during the scan was videotaped for further analysis. This
information is later digitized using the new Data
Translations High Resolution Frame Grabber, which
digitizes the real-time video signal for further
processing by the IRIS Image Processing Computer System.
The thermal image signal is broken down into a 16 color
temperature scale, and temperatures/colors are assigned
to the radiational intensities of the image.
The information can
now be presented as colorized thermograms, with different
colors representing different surface temperatures.
Variables that can affect the thermal radiation include
wind velocity, cloud coverage and material density. A
color bar along the bottom of the thermograms indicate
temperatures in ascending degrees with warmer areas at
the right of the bar.
Matching black and
white thermograms are also included. These thermograms
can help in locating anomalies when matched with the
colorized thermograms and the visible light photographs.
Keep in mind that the infrared wall survey is identifying
changes in temperature of as little as .10 F. degrees.
The thermographic information is carefully analyzed and
reviewed a number of times by trained thermographers, to
be sure anomalies are not overlooked.
Corresponding
visible light photographs help to orientate the
thermograms, as well as give clues to water entry points.
All three photographs are included in the illustrations
section of this report. The thermograms are positioned on
one page, with the visible light photo appearing on the
opposite page. Some thermographic sets utilize the same
visible photo as the preceding set.
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EVALUATION
The review of the
thermographic images recorded during July 12, 1995
indicated moisture infiltration within the masonry in
select locations. These areas can be found in the field
of the walls, and above and around windows and vents.
Seen by the camera
are what appears to be:
1. Cracked and
debonded mortar joints.
2. Broken or
cracked bricks.
3. Parapet wall
moisture entry at select locations.
4. Leakage at
or near window lintels, sills and frames.
Moisture that
enters the building from below grade will not be seen by
the infrared camera.
The survey
successfully isolated each of these items, which can be
viewed in the Illustrations Section of this report. The
causes of water entry are indicated in the descriptions
of the thermographic sets. Arrows point to the anomalies
seen in the thermograms.
Any entrapped
moisture within the masonry could be cause for future
deterioration. Prolonged exposure to water at these
locations will deteriorate the wall at a rate that will
increase with exponential speed the longer the problem
remains.
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ILLUSTRATIONS
During the infrared
survey of the select elevations at the Long Branch High
School, thermal data was recorded on videotape and later
processed to create the following thermograms. Each set
of photographs depicts one sample area as a colorized
thermogram, black and white thermogram, and a visible
light photograph. Only contracted wall segments were
scanned during the survey of July 12, 1995.
The colorized
thermogram depicts moisture affected wall components as
changes in color, typically blacks and reds.
The black and white
thermogram depicts wall thermal anomalies as dark spots.
Some appear as single bricks, multiple bricks (cracks in
the mortar joints) and entrapped moisture behind the
walls.
The visible light
photographs are taken from the same location as their
corresponding thermograms and depict the same field of
view.
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In this portion
of the wall, moisture is again seen above the
windows, especially over this area indicated by
the arrow. Two other patterns are seen here,
indicating debonded mortar joints, cracked
bricks, and possibly split caulking in a control
joint. They are indicated by the arrows. The
truck blocks the view of the lower window (VLP).
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This elevation is
experiencing severe interior moisture damage. The
patterns show moisture over the window, and a
general absorption through the masonry at the
area indicated by the arrow. If the building has
been waterproofed, it is possible that this area
was not treated sufficiently.
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A major crack in
the brick and mortar can be seen is the upper
left corner of the wall. Also seen is water above
the window lintels.
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Major masonry
cracks are seen in the upper right corner of this
wall. Also, substantial moisture is seen entering
above and to the right of a lower window.
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The major
problems seen in the last thermographic set can
be seen closer here. Severe cracking of the
bricks and mortar allow large quantities of water
to enter. The arrow points to a large moisture
pattern in a nearby wall elevation.
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Another major
crack in the wall creates this clearly
identifiable thermal pattern. The crack extends
from the corner of the wall to the window.
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