Tech Tip: Ring Around the Bullseye

Pressure Ring or Trapped Air?

Part One: Pressure Rings

A recent post on windshield-repair-forum.com brought to my attention that even some experienced windshield repair technicians are very confused about the cause of the ring around the outside of a bullseye, which is sometimes visible after the completion of a windshield repair. It’s time to separate the facts from the fallacy.

To be fair, there are several possible causes for a ring around a bullseye, and understanding the cause is the key to identifying what you are seeing. In this three part series, we will explore the primary causes.

A pressure ring is translucent; it has no color, and has a bit of a watery look to it.  What you see is the resin trapped between the glass and the Polyvinyl Butyral (PVB). Causes include:

Excessive pressure.

If the resin is forced into the damage under excessive pressure, it can separate the PVB laminating material from the glass.

• This is a form of separation or delamination, sometimes referred to as “flowering” or “the daisy effect,” because if the damage is severe enough the resin trapped between the PVB and the glass resembles the shape of a flower. On a bullseye it is typically a symmetrical ring around the outside of the damage, commonly referred to as a “pressure ring.” On a crack or star break it will generally follow the shape of the damage with just a fine watery looking line.
• It does not take a great deal of pressure to inject resin into most damage, and very little pressure to fill a bullseye. Do not use more pressure than necessary and avoid the use of injectors advertised as “high pressure.”

Excessive heat.

• Heat causes the PVB to soften, allowing resin that has been injected under pressure to separate the glass from the PVB.
• Adjust glass and resin temperatures to the Delta Kits recommended range of 70° – 90° Fahrenheit prior to starting a repair whenever possible. If the glass is warmer than the recommended temperature range, start with less pressure than normal.

Old glass.

• Over time the glass layers will begin to separate from the PVB sandwiched between them, most often beginning with the edges of the glass where the PVB is exposed. While this is very common in vehicles that are over 10 years old, the delamination process may actually start much sooner.
• Check the edges of the glass for signs of delamination prior to starting any windshield repair. Even without resin between the layers there may be a watery appearance, or if water has entered into the air space left by the separation there may be a milky white appearance. You may also see signs of delamination around rock damage in the windshield, indicating that not only is the windshield beginning to deteriorate, but that the damage is not new.
• If any signs of delamination are noticed prior to starting a repair, notify the customer and explain that while you will do everything possible to minimize the chances of delamination around the repaired area, a windshield that has already begun to deteriorate is very susceptible, so there is always a possibility of a pressure ring or flowering.

A combination of heat, pressure, old glass and old damage.

• Where technicians really get into trouble is when working on old damage, on an old vehicle, in the hot sun, and using excessive pressure. The combination of these four things is a recipe for disaster. A one inch combination break can quickly become a six inch delamination nightmare.

Delamination around an existing rock chip indicating an old windshield and old damage.  Proceed with caution after advising the customer!

This concludes part one of our three part Ring Around the Bullseye series. In part two we will examine trapped air.