2002 GMC Sierra 1500HD Roof Rust Repair
The Sierra 1500HD that will be pictured in this thread.
The truck began showing obvious signs of rust propagating from the backside of the sheet metal surrounding the third brake light. Chevrolet trucks are notorious for issues with water intrusion from under or through the third brake light assembly. This particular example was caused by water intrusion through the driver side mounting screw due to a poor seal and a very small fracture underneath the screw. The screws pass internal to the light seal and allow a direct path to the interior sheet metal. Evidence of moisture intrusion may also be present on the headliner inside the vehicle during severe cases. I would strongly recommend periodically checking the condition of both your light assembly as well as the condition of the seal underneath.
This photo shows the condition of the metal after putting light pressure on the affected areas. As you can see, many sections fell right through to the interior compartment.
Realizing that the damage was significant, I went ahead and Roloc'd the damaged areas back until clean metal was exposed.Unfortunately, the back side of the sheet metal showed even more extreme rust scaling. It was at this point that I realized the damaged areas would need to be cut out and a patch panel would need to be grafted in place.
I measured and marked the area that I chose to cut out. Notice the tape line in the center of the third brake light opening. This would be my reference point for centering the new panel.
No turning back now! As my dad stated, "cutting the roof open on your girlfriend's truck is not for the faint of heart." No fear here though, I wanted the repair done right. Which meant removing any and all damaged metal.
The extent of the rust damage was obvious once the original panel was removed.
The existing roof structure was panel flanged and a patch panel from a donor vehicle was sized and cut to fit.
The flanged area was ground to bare metal and the surface was prepared with a 40 grit Roloc at low speed to leave the proper tooth for the panel bond adhesive to bond to.
Both the roof and the patch panel were coated with high-grade professional panel bond adhesive. It's important to be sure that all bare metal surfaces are 100% coated with the panel bond to ensure proper corrosion prevention.
The panels were joined and clamped in place for the full 24 hour cure time of the adhesive. Some of you may be wondering why I chose to bond a patch panel in place, rather than weld. Panel bonding technology has become the industry standard because of its superior corrosion prevention. It also eliminates sheet metal distortion from the heat generated from welding.
After cured, the excess panel bond was ground flush and the area around the joint was ground to bare metal to allow the first stage of filler to properly adhere to the repair.
I chose to fill the immediate area around the joint with fiberglass reinforced filler. This will add strength to the joint as well as helping to prevent repair mapping in the final finish.
The first round of filler was blocked down with 80 grit sandpaper until the repair was relatively flush.
A coat of high-grade polyester filler, that was tech sheet approved for use over cured OEM paint substrates, was laid over the repair area and beyond. This will be block sanded smooth and straight to level any inconsistencies in the sheet metal caused by the repair and further prevent repair mapping.
This photo shows the final layer of filler after block sanding. This step was finished with 180 grit sandpaper to prepare for primer.
Several chips on the roof had begun showing signs of surface rust. While we were repairing the rear portion of the roof, we wanted to ensure that none of the other areas were left to worsen in the future. So they were Roloc'd down to clean metal and prepared to fill.
There were 10+ areas that needed to be addressed. This image shows them after they were filled and blocked level in preparation for primer.
All repair areas were covered with three coats of 2K urethane primer. They are now ready for the next round of block sanding.
Here's the roof, ready for paint, after several more coats of primer and a few rounds of body work.
Here's the finish after several coats of clear.
A quick snap shot of the project start to finish.
The roof was refinished using PPG Deltron base coat and PPG JC60 clear coat. It's a relief to have the roof rust-free and back to factory finish! On to the next project!