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Masonry Wall : Long Branch High School, Long Branch, NJ

Infrared Analysis
Long Branch H.S.
Investigation: 7/95

Table of Contents

  1. Abstract

  2. Evaluation

  3. 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.

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).

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.

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.

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.

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.

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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