by Bob Beranek
  • facebook

What is a flap?” A flap is a sliver of cured urethane lying on top of another piece of cured urethane, which can cause a leak or bonding problems. Any time you are replacing a windshield and stripping back the existing bead, flaps in the urethane must be eliminated.

A flap can be caused by the cut-out procedure, strip-out procedure or by a combination of the two.

A flap can be caused by the cut-out procedure, strip-out procedure or by a combination of the two. Often, a flap is not noticed by the technician due to insufficient light, compressed timelines or the (proper) practice of not touching the bead after the strip-out procedure.

We never want to create a flap, but it can be easy to do. For example, using a cut-out tool in one direction and then finishing the cut-out action in the opposite direction can cause a flap where the start and stop points overlap. Most of the time, this flap is eliminated by the strip-out action of the full strip process, but if the flap is deep enough it can go unnoticed. The sliver left behind is almost invisible to the technician and easily missed.

If the flap is deep enough it can go unnoticed.

A flap can also be caused at the start and end point of the strip-out procedure, where the technician trims back the existing urethane bead. Again, a flap can be created if the tech strips the urethane in one direction and then finishes in the opposite direction.

If a flap is not discovered and eliminated, the new fresh bead of urethane is applied right over it, which can cause an entry way for water into the vehicle. The flap also creates a bond problem.

The first step in eliminating flaps is to realize they exist, and to look for them. Use your strip-out tool to find possible flaps within your trimmed-back bead. Gently run the tool over suspected areas, and try to catch the blade on the loose flaps. Once found, cut them off.

Try to catch the blade on the loose flaps.

I know it’s easier to use your gloved hand to find the flaps, but you run the risk of contaminating the freshly exposed existing bead with your gloves. If you must use your hand to find and eliminate a flap, make sure you wipe the surface clean according to your adhesive manufacturer’s instructions.

The flap leak can be difficult to fix. With other leaks, a little bead of fresh urethane placed over the leak area will work. However, with a “flap leak” this technique may only shift the water leak to another location. The best way to fix the leak is to remove and install the windshield. However, if you decide not to do a full removal and installation, I suggest the repair bead be extended the entire length of the roofline and down the sides an inch or two. This will divert the water and have a better chance of sealing it for good.

You run the risk of contaminating the freshly exposed existing bead with your gloves.

Don’t forget, the best thing to do is not have flaps in the first place. Take the time to look and eliminate them.

I hope everyone is having a happy and profitable 2017.  Last year was an eventful (and sometimes frustrating) year for the AGR Industry, and I predict 2017 will not be any different. New dealer directives on glass and part usage and the expectation of new calibration tool introductions will prove to be exciting and challenging.  Keep visiting this site for updates as they happen.

Today, however, I want to address a problem that can be solved with chemistry and a little extra effort. With the increase in underside mouldings, lower cowl retaining devices and self-adhesive clips, we all have faced the challenge of getting these products to adhere aggressively to plastic and painted surfaces. To put it bluntly, many of these products just don’t stick the way they should.

In the case of self-adhesive moulding clips, technicians have attempted to fix the problem with the use of “liquid clips” and a length of tape to hold the moulding down until the urethane cures. This is not the way mouldings should be reinstalled. For consistent performance, clips should be properly adhered, and the moulding attached to the clips by design.

Proper cleaning and preparation of surfaces is the key to making added parts stick during an installation. I instruct the use of self-adhesive parts this way:

  • Clean both surfaces of any residue;
  • Warm the adhesive tape to body temperature; and
  • Press in the part place for five or more seconds to allow the adhesive to bond.

The Material being prepped for application

This process works consistently if you make the effort to follow the process. However, if any of the three steps above are not followed, the result is adhesive failure – with the mouldings, cowl or clips coming loose and flying away at highway speeds.

However, I’ve recently learned about other products that can help “add on” parts stick to surfaces. At an auto dealership training course I gave last month, the body shop manager showed me a product meant to be used with double-faced tape. The generic name is an adhesion promoter.

The foam applique being applied.

I was amazed at the difference this product can make. Adhesion promoters are used routinely in body shops, but I believe they are very practical in the AGR industry, too. The directions are simple;  apply the promoter to the cleaned surface (or surfaces) that will be attached by the adhesive tape, allow it to dry 60-90 seconds, and then press into place. Once you use it the first time, you may never want to be without it again.

There are a number of brands of adhesion promoter out there, so do your own experimenting. Some products are in bottles, some are in individually wrapped packages, some have applicators and some are in saturated sponges for ease of use. Contact me at if you have experience or suggestions for using them.