The daisy effect

May 1, 2007
AUTO

Editor’s note: This article is the first in a series addressing technical questions regarding windshield repair, courtesy of the National Glass Association’s National Windshield Repair Committee. For answers to these and other repair-related questions, visit www.windshieldrepair.org.

What causes a completed repair to look watery around the edges, and how can this be avoided?
Commonly known as “the daisy effect,” “halo effect” or “flowering,” this problem occurs when the resin flows out between the outer layer of glass and the inner PVB layer of a windshield. In mild cases, a technician might experience a single thin line around the perimeter of a bullseye, or along the edges of a star break. In extreme cases, the resin is forced out several inches beyond the perimeter of a combination break. Although not typically a structural problem, this can significantly diminish the cosmetic quality of a finished repair.  

There are three main causes of this unsightly problem: excessive heat, excessive pressure and de-lamination. De-lamination typically occurs in older windshields.

Excessive heat
Excessive heat softens the PVB layer of the windshield, and even under minimal pressure, allows resin to seep between the PVB and outer layer of glass. How hot is too hot depends on how much pressure is used to inject the resin and the age and condition of the windshield. Most equipment manufacturers agree that a windshield should not be repaired when the glass temperature is more than 100 degrees Fahrenheit. Always follow your equipment manufacturer’s recommendations for proper working temperatures.

In most cases, you can cool the windshield by simply shading the glass for a few moments prior to performing the repair. Reducing the interior temperature of the car also helps. However, do not direct cold air toward the windshield, or use cold water, as the sudden temperature change can cause the damage to spread.

If it is necessary to heat a windshield, do so slowly, heating an area of at least several inches around the break. Never allow the glass temperature to exceed 100 F.

Excessive pressure
Excessive pressure has the same effect as excessive heat. The amount of pressure required to fill a break varies from system to system, but obviously the higher the pressure, the more likely you are to experience the daisy effect. Always follow recommended procedures for applying pressure, and never use more pressure than necessary to fill a break.

De-lamination
Even in the best of situations, windshields begin to de-laminate with age. When subject to heat, cold and moisture, the de-lamination process accelerates. In some instances, de-lamination is present at the edges of relatively new windshields, but generally it does not show up until the glass is at least 5 years old. De-lamination is common in windshields that are older than 10 years.

Always check the entire windshield prior to beginning a windshield repair. If there is any indication of de-lamination, inform the customer of the possibility of a daisy effect. If the de-lamination is severe, encourage the customer to replace the windshield rather than repair it.
While any one of these three causes can create a daisy effect, the problem is most common when one or more of the conditions are present. To avoid the daisy effect, monitor and control the glass temperature throughout the repair process, do not use more pressure than necessary to fill the damaged area, always check the windshield for signs of de-lamination prior to starting the repair process and use extra care when repairing windshields that are more than 10 years old.