Anti-Corrosion Treatment; Sheet Metal Repair - GMC G Service Manual

ANTI-CORROSION TREATM ENT
This vehicle was designed and built to resist corrosion.
Application of additional rust-inhibiting materials is not nec­
essary or required under the 6-year/100,000 mile corrosion
coverage.
• Some after-manufacture rustproofing may create a
potential environment which reduces the corrosion resis­
tance designed and built into this vehicle.
• Depending upon application technique, some after-man-
ufacture rustproofing could result in damage or failure of
some electrical or mechanical systems of the vehicle.
• Repairs to correct damage or malfunctions caused by
after-manufacture rustproofing are not covered under
any of the GM New Vehicle Warranties.

SHEET METAL REPAIR

To help prevent rust, special anti-corrosion materials are
used on interior surfaces of metal panels. These materials
include special metals such as one-sided and two-sided
galvanized, zincrometal and zinc-iron alloy steels. These
specially-treated materials are used in fenders, doors,
quarter panels, rocker panels, floor pans and other critical
areas.
Spray-on materials such as zinc-rich primers and waxes
are also applied to interior surfaces. These are mainly used
in areas where moisture might gather. Sealers are applied
along exposed joints, and moisture-repelling asphaltic
sound deadeners are applied inside wheel wells and doors,
and on some underbody parts.
If these special treatments are disturbed while repairing
damaged areas, the metals may be left unprotected. This
could lead to corrosion; therefore, these surfaces should be
recoated with sen/ice-type anti-corrosion materials. Use the
following steps in applying the materials.
1. Clean-Up and Preparation
Depending on the location of the area, sandblasting,
scraping, wire brushing, sandpaper and steel wool
may be used to remove residue.
SHEET METAL 2B-29
2. Applying Primer Coats
Prime all bare metal with an acrylic chromate
material.
3. Applying Sealers
Seal all flanged joints, overlap joints and seams with
a medium-bodied sealer which stays flexible and is
paintable.
Use a heavy-bodied caulking material for all open
joints which require bridging of sealer to close a gap.
4. Applying Color
If areas such as underbody, hem flanges, exposed
joints and engine compartment need color, follow
conventional refinishing preparation, undercoat build­
up, and color application procedures. Rub-out and
extensive sanding of the undercoats is not necessary.
5. Applying Deadeners
Use a heavy-bodied undercoat with a rubberized or
asphaltic base. Areas for application can be deter­
mined by original production application.
6. Applying Anti-Corrosion Material
Use a light-bodied material designed to penetrate
between close metal-to-metal surfaces such as
pinch-weld joints, hem flanges, and other attaching
points where metal surfaces are difficult to coat with
conventional materials.
7. Conventional Undercoating
Apply to large areas such as doors, hoods, fenders,
etc. Use care not to spray material into door hardware
such as locks, run channels and window regulators.
On the underbody the material should not be applied to
any moving or rotating parts.
After undercoating, make sure that all body drain holes
are open.