Lamination separation (LS) is real and should be taken seriously. Most LS shows itself on a windshield’s edges, where the bonding occurs. Windshields are made from two layers of regular annealed glass and an inner layer of polyvinyl butyral or butyrate (PVB). Annealed glass used in windshields is the same type of glass used in picture frames and is usually about 9 mm thick per piece and offers little strength on its own. The strength and “safety” come when matching pieces of glass and the PVB fuse together. If the three parts separate when it’s being assembled the windshield is greatly weakened and the bond is compromised.
There are two ways LS shows itself, a cloudy, milky appearance and small bubbles usually appear near the glass’ edge. It’s usually caused by excessive heat which shrinks the vinyl lamination or by the intrusion of moisture between the two layers of glass that causes it to separate.
When bubbles are found, they occur primarily on the edges, due to the black frit paint that absorbs more heat generated from the sun. Depending on the amount and extent of the bubbling, the safety of the glass will be impacted. If you have LS, the adhesive only fuses the inner layer (9 mm of glass) to the frame, and not the whole glass assembly.
The cloudy, milky separation is caused when moisture in between the layers of glass. You’re seeing the laminate (PBV) reverting to its pre-autoclave condition, which has an opaque appearance. This also is a dangerous condition, because of the separation’s extent, for safe glass bonding. This type of separation’s cause can sometimes be the unsealed edge of the glass.
Those of you that have glass fabrication as an add-on to your services, probably have noticed if the edges of a freshly cut laminated glass part is not sealed after fabrication, a cloudy appearance may appear with time and exposure to the elements. This is because when cutting the lamination while processing the part, the lamination is stretched. Then the PVB is allowed to relax which causes it to recess between the two layers of glass that cause an access point for moisture, which allows it to separate the two layers of glass.
LS is mostly in the southern or hotter climates, though it does happen due to poor manufacturing as well. The cloudy conditions can be caused by glass fabrication but also by improper preparation of the windshield prior to installation. If the edges of the glass must have the excess lamination trimmed off for moulding fit or any other reason, make sure you seal the edges with your black primer. That way the edges are sealed and the cloudy separation will not occur.