Photo Courtesy of Trifive.com

I can always tell when a technician was trained by an “old-timer” like me. How? They “spank” or slap the glass into position rather than smooth it in place to make the seal. It comes from the old days when glass had to be spanked and seated into a gasket or when dense butyl tape needed to be forced down to contact uneven pinchwelds. Liquid urethanes call for smoothing the seal, not spanking or slapping the glass into place.

First, let me say it’s not necessarily wrong to slap the glass. It is, rather, ill-advised. There are two negative results that can happen when a glass is slapped rather than smoothed.

• If the glass is thin, chipped or scratched, then the chance of premature breakage is increased. If the glass is “hot,” the glass is more volatile and can fracture. Some of these issues can and should be caught by the technician prior to installing. However, how hard is too hard to slap the glass into place? It only takes one break to lose your profit and possibly a customer to inconvenience.
• The second negative issue involves leaking and bonding. Curved glass has a spring to it. It can be depressed as much as a couple of inches before breakage and then sprung back to its original shape or curvature. If the bead of urethane is short and the glass is slapped at its apex, it can make contact and then “string out,” causing leaks and bonding problems. If it is smoothed-out, the urethane bead is redistributed into weak areas, making for a more solid bond and leak-free installation.

If I said I never spanked or slapped the glass, I would be a liar. There are instances where a slight slap is necessary. If you have a large, tall or awkward vehicle where leveraged pressure can’t be applied to the edge of the glass, such as in large service vans, then a slight tap on the top and bottom center may be called for. Of course, this is after a careful inspection of the glass part conducted during the prep stage and that the glass is not exposed to excessive heat.

My advice is to use slapping only when you must and only when the glass was carefully inspected for pre-installation damage. Keep the glass out of bright hot sunlight for as long as possible prior to installation into the opening. Reduce the violence used in past installations as much as you can. The customer will feel less anxious if watching the process and vehicle and glass damage will be reduced to increase profits.