If you have been repairing windshields for very long, you have likely encountered a problem with some repairs having a watery appearance around the edges.
This problem is known by a number of names including, the daisy effect, the halo effect, or flowering, but what it refers to is resin that flows out between the outer layer of glass and the PVB (center layer) of a windshield. In mild cases a technician might experience a single thin line around the perimeter of a bulls-eye, 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, the cosmetic quality of the finished repair can be significantly diminished.
There are three main causes for this unsightly problem, excessive heat, excessive pressure, and de-lamination. De-lamination is typically found in older windshields.
1) Heat: Excessive heat will soften the PVB layer of the windshield and even under minimal pressure will allow resin to seep between the PVB and the outer layer of glass on the windshield. How hot is too hot depends on how much pressure is used to inject the resin, the age of the windshield, and the condition of the windshield, but most equipment manufacturers agree that a windshield should not be repaired when the glass temperature is over 100º Fahrenheit (38º Celsius).
a. In most cases the windshield can be cooled by simply shading the glass for a few moments prior to performing the repair. Reducing the inside temperature of the car also helps. Cold water and ice are not recommended as the sudden temperature change can cause the damage to spread.
b. If it is necessary to heat a windshield, do so slowly, heating an area of at least several inches around the break, never allowing the glass temperature to exceed 100º Fahrenheit (38º Celsius).
2) 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. For this reason high pressure systems should be avoided.
3) De-lamination: Even in the best of conditions windshields begin to de-laminate with age. When subject to heat, cold, and moisture, the de-lamination process is accelerated. In some instances de-lamination is present at the edges of relatively new windshields, but generally de-lamination does not show up until the glass is at least 5 years old. De-lamination is very common in windshields that are older than 10 years.
a. Always check the entire windshield prior to beginning a windshield repair.
b. If there is any indication of de-lamination the customer should be informed of the possibility of a daisy effect. If the de-lamination is severe, the customer should be encouraged to have the windshield replaced rather than repaired.
Summary: While any one of the three causes stated above can cause the daisy effect, the problem is most common when two or more of those 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 over 10 years old.