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. 

California Failure Analysis Expert Witness Examines Window Damage

Window cleaning is an important final step in finishing off construction of a building. This fact is sometimes ignored, and improper cleaning results in significant damage to the new windows. This in turn leads to a lawsuit. The glass association of North America (GANA) has published a bulleton to instruct as to the proper window cleaning procedures, and it strictly prohibits the use of  metal blades. Above are photographs of two examples of the type of window damage caused when blades are used to clean windows on new construction. This damage was discovered during a window damage failure analysis.  These windows are two of over 1000 showing window scratching from window cleaning damage. The parallel nature of the scratches indicates that dirt was caught under a metal blade and dragged across the window and scratched the surface.

Glass Expert Analyzes WIndow Damage

Glass failure analysis expert analyzes scratched windows on new construction. There have been numerous occasions where a glass expert has been brought in the determine the cause of window scratching. This is often on new construction that has a stucco exterior. Post construction window claening is critical because of adhered construction materials. Removal of these materials is difficult because of their adhesion. Therefore, cleaning crews should not use blades to remove debris. In many cases abrasive debris such as stucco or cement can be captured by the blade and scratch the glass as the blade is being drawn across the surface. Abrasives can also be captured by dry cloths and pads and can also cause window scratching. The photographs above show the resulting window scratches. Upper left is a sample of cloth related window scratching, and upper right is a sample of metal blade related window scratches. These are window cleaning related and are not manufacturing defects. Only experienced window cleaners should be assigned to clean windows on new construction.

GLass Expert Discusses WIndow Failures and Window Evaluations

Glass experts at Read Consulting provide services as window experts. Read Consulting offers a wide spectrum of window testing and evaluation. Included are glass failure analysis, evaluation of window damage and window scratching, window performance (light transmission testing of low-E windows), problems with laminated glass, temper level of tempered and heat strengthened glass, nickel sulfide induced failures of tempered glass and window distortion. These services are a natural outgrowth of continuous involvement with glass, glass properties and useable items made from glass.