Window Defect Analysis Capabilities

Reflected Zebra Board Image that Shows
Window Roller Distortion Created
During The Thermal Temper Process

Window Scratches Caused by Poor
Cleaning Procedures

The window experts at Read Consulting are often asked to evaluate windows for defects. Many of these are Low-E windows that are also tempered. Two typical defects found are scratches and roller distortion.
Often the scratches are created during post construction cleaning. Roller distortion is formed when the float glass windows are thermally tempered.
Window Scratching: This is evaluated per ASTM C 1036 and is graded by the visibility of the scratches under controlled light conditions. Typical cleaning scratches are demonstrated in the above photo.

Window Roller Distortion (Tempered Glass Roller Distortion): This is evaluated per ASTM C 1048. Distortion in reflection using s standard "zebra board" (i.e. a standard striped pattern).  The photo above shows a sample of roller distortion found on a coated window. This test was done by reflecting the zebra board off the window outer surface. This test was performed on both window exterior surfaces. Often the amount of distortion allowed is defined by the construction contract. 

Glass Experts Examine Hotel Window Defect

 The glass experts at Read Consulting performed a window defect analysis on defective windows at a hotel. The windows began to appear dirty, and no amount of cleaning could remove the "dirt". When initially installed, the insulated glass (I.G.) windows appeared normal. However, over time they began to appear perpetually dirty. Using a microscope to look through the glass from surface 1, it appeared that surface #2 was heavily scratched. The window was disassembled and surface #2 was examined directly with a microscope. The defect was found to be in the Low-E coating on surface #2. This is a manufacturing defect and not the fault of the building owners. Product liability rests solely with the manufacturer.

Glass Expert Performs a Window Defect Analysis

California glass expert was asked to analyze a window defect that appears as a streak in the window. The glass failure analysis showed that the streaks in the window were  strings of bubbles near the surface of the glass. Upper right is a photograph of the window defect which appears as streaks. Upper left is a macro-photograph of the near surface bubbles that cause the defect. This is a manufacturing defect.

Manufacturing Defect on Tempered Glass Window

Glass failure analysis expert witness performed a root cause failure analysis on window defects found on a recently built custom home. The upper left photograph shows the defect from the building exterior. The window defect resembles a dust or dirt streak and was not detected until the post construction window cleannig. In all cases, the manufacturing defect is in the center of the window, is parallel to the long side and it looks like a streak or scuff. The upper right photograph is a 200X photomicrograph of a portion of the window defect. It is composed of an array of small glass particles strongly adhered to the glass surface. It is believed that these particles were generated during the window sizing process and were a contaminant on the horizontal rollers used in the glass temper process. During glass tempering they came into contact with the hot glass surface and welded to it. This is a manufacturing defect. It is not a construction defect. This defect is often blamed for window scratching from window cleaning operations. However, these particles were visibly obvious and could not be dislodged. Therefore, these particles don't fit the popular window damage model proposed by many window cleaning experts.