Pinchweld Prep During Collision Repair

While conducting a training course recently, I covered the proper steps for prepping a pinchweld after a collision repair.

I was surprised to hear that my mostly experienced audience did not know that it is necessary to tape up the pinchweld after the primer coat and before the color and clear coat is applied.

The typical coatings applied to the bare metal of a new vehicle’s body consist of:

  • An electrodeposition coating or “etching” primer. This coating gives the bare metal corrosion resistance.
  • You apply body primer on top of that coat.
  • Once the primer coat is cured thoroughly, you should apply the color coat.
  • Finally, you cover the color coat with the clear coat.

These coatings are then baked to meld them together, and to produce a long-lasting durable finish that will resist corrosion and hold the color without fading. In most cases, glass parts are then bonded to the melded finish. Federally mandated crash testing proves this method easily meets the Federal Motor Vehicle Safety Standards that regulate windshield retention.

Problems can occur however, when the vehicle needs repair after a collision. Most collision repair shops cannot replicate the original paint job. Body shops must rely on chemical-curing coatings because the vehicles are rarely stripped of all interior parts, and baking a vehicle at OE temperatures would melt and damage parts left in the vehicle during repair. These chemical curing paints do not have the strength between coatings to meet the requirements for stationary bonded glass parts.

All adhesive companies and collision repair training organizations instruct their collision repair technicians to tape off the glass bonding area of the pinchweld before the color coat or clear coat is applied. The reason for this is the aftermarket color and clear coats cannot meet the tensile strength necessary to hold the glass in place in the event of a collision. However, the primer coat can. The primer to “E” coat adherence is strong enough to withstand the forces dictated by the federal standards.

The proper procedure to follow and to communicate to your collision center customers is as follows:

  • You should start by removing the glass part. Do not strip back the existing urethane. Leave the existing urethane in place until right before reinstallation.
  • Next, you should instruct the body shop technician or paint professional to tape off the floor of the pinchweld after the “E” coat and primer coat is applied and cured.
  • The painter can now apply the color and clear coat.
  • When the glass technician returns for reinstallation, be sure to remove the pre-applied tape and strip back the remaining existing urethane, leaving 1-2 mm.
  • Next, prime the exposed primer coat with urethane metal primer and bond it accordingly.
  • If the body shop technician does paint the bonding surface of the pinchweld, you are required to abrade off the color and clear coat to the primer level and follow the step above.

This procedure will restore the strength necessary to meet FMVSS 212 and 208. If the steps listed above are not followed, the installation is compromised, and the bond is only as strong as the strength between the primer and color coat. That is not enough.