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RUST REPAIRS
Tool and Material Checklist:
- Masking tape
- Fiber-glass reinforced filler
- Lightweight air grinder
- Assorted sandpaper
- Metal conditioner
- Sanding block
- Rust deactivator
- primer
- Clean cloths
- Wire brush or scraper
- Safety glasses or goggles
- Chemically Impervious
- Air filtering mask gloves
- Plastic spreader
Corrosion damage on a car takes two forms: surface rust and rustouts. In its early stages, surface
rust is a reddish coating on the metal. In time, the
rust eats pits into the surface. These pits eventually develop into holes, or rustouts. Each type of
damage requires a special repair procedure, both
of which are covered in this booklet. When doing
the procedures, do not skip any steps-there are
no shortcuts to good auto body work.
SURFACE RUST
Areas affected by light surface rust can be re-
paired simply by grinding the rust away and applying a coat of metal conditioner. If the metal is
pitted, however, additional steps are needed.
Preparing the Surface
1. Wash the affected area with water and mild
detergent, then clean with a wax and grease
remover.
2. Apply masking tape to the surrounding trim
to protect it when grinding.
3. Use a hand sander or scraper and #36 or #80
grit paper, or a lightweight air grinder and #24 grit
rigid sanding disc to remove the surface rust. Hold
the grinder against the car at a 10o angle and use a
back and forth crosscutting action. When moving
the grinder to the right, press the upper left corner
of the disc against the metal; when moving to the
left, put the pressure on the upper right corner.
NOTE: Always wear safety glasses or goggles
when grinding. To avoid breathing paint and sanding dust, an air filtering mask should be worn.
4. If necessary, use hand tools or a die grinder
attachment to remove rust from the pits, panel
edges, and other hard-to-reach areas.
5. Use metal conditioner to etch the surface and
improve the bond between the metal and the primer. It must be diluted before using; follow the
manufacturer's instructions.
6. Apply the metal conditioner with a clean cloth
and use a separate cloth to wipe it off before it
dries, If the conditioner dries before it can be re-
moved, rewet the panel and wipe it dry.
NOTE: Always wear safety glasses or goggles
and chemically impervious gloves when handling
metal conditioner or rust deactivator.
Applying Filler
1. To prepare the filter, first place the required
amount of resin on a mixing board.
2. Knead the tube of hardener thoroughly, then
squeeze a narrow ribbon across the glob of resin.
This will provide the correct proportion of resin to
hardener.
3, Mix the resin and hardener with a plastic
spreader, using a firm, flat wiping motion. Do not
stir; this will trap air in the filler and form pinholes.
4. The filler will begin to harden after a few minutes. Use the following table to determine how
much working time you will have.
| Temperature |
Working Time |
| 100oF |
3 to 4 minutes |
| 85oF |
4 to 5 minutes |
| 77oF |
6 to 7 minutes |
| 70oF |
8 to 9 minutes |
5. Continue mixing until the filler is a uniform
color. Use the color guide on the package to judge
the accuracy of the mixture. If it is too light, add
more hardener; if it is too dark, add more resin.
6. Scoop up some of the filler onto the edge of
the spreader and spread a thin skim coat over the
pitted area. Use moderate pressure to force it into
the pits.
7. Allow the filler to harden, then block sand
with #80 grit sandpaper until the filler becomes
level with the metal. Use compressed air to blow
away any excess filler dust.
NOTE: Always wear safety glasses or goggles
when blowing with compressed air.
8. If necessary, apply another skim coat of filler.
Wait until the filler has dried completely before
proceeding.
Sanding and Priming
1. Final sanding and priming are important to
achieve a smooth, professional-looking finish.
Begin by wet sanding with #400 grit sandpaper
and a sanding block. Use long, straight strokes to
avoid creating low spots.
2. Clean the sanded surface with a tack cloth,
and dry thoroughly.
3. Spray primer over the repair area and several
inches of the old finish around it. Allow the primer
to flash (surface dry) for five minutes.
NOTE: Always wear safety glasses or goggles
and an air filtering mask when spraying primer or
paint.
4. Wet sand lightly with #240 grit sandpaper,
then clean and prime once or twice more. Between
coats, wet sand lightly with #400 or #600 grit sand-
paper to achieve a very smooth surface.
SMALL RUSTOUTS
Spots of surface rust can be a sign that rust has
eaten through from the backside of the panel. Re-
pair small rustouts immediately before they be-
come bigger problems.
Preparing the Surface
1. Grind the repair area with hand tools and #36
or #80 grit paper, or use a lightweight air grinder
and #24 grit rigid sanding disc.
2. Use a pick hammer to bevel the edges of the
rustout. This will remove any loose rust and paint,
as well as create a depression to prevent the filler
from falling through the hole.
3. If the backside of the panel is accessible, use
a wire brush or scraper to remove accumulated
dirt and undercoating.
4. Apply a rust deactivator to the rust to seal out
air and moisture and prevent further oxidation.
5. Apply metal conditioner to the bare metal.
Applying Filler
1. Plug all rust holes with waterproof, fiberglass-
reinforced filler. (Regular plastic fillers absorb
moisture and should not be used.) Use a plastic
spreader to work the filler into the holes.
2. Allow the filler to harden, then sand smooth.
Wipe away excess dust with a clean cloth.
3. Cover the holes with a layer of regular plastic
filler.
4. After the plastic turns rubbery but before it
hardens, knock off the high spots with a cheese
grater. Hold the grater at a 10° to 20° angle to the
surface and pull it across the repair area.
5. When the filler has completely hardened,
sand it down, level with the metal. It is now ready
to be finish sanded and primed as described
earlier.
LARGE 'RUSTOUTS
Rust on the underside of a panel is not usually
noticed until it has attacked a large area of metal.
If left unattended, the rust will spread until it has
eaten a gaping hole in your car. Large rustouts are
not only unattractive, they can also affect the structural integrity of a vehicle. Structural
members with large rustouts should either be re-
placed entirely or the rusted area cut away and
new metal installed, Of course, the age or overall
condition of your car might not warrant these
more expensive repairs, so this procedure uses a
relatively inexpensive fiberglass cloth patch and
resin liquid.
Preparing the Surface
1. Cover all surrounding trim pieces with masking tape to protect them when grinding.
2. Use hand tools and #24, #36, or #80 grit
paper, or a lightweight air grinder and #24 or #36
grit rigid sanding disc to remove as much loose
paint and rust as possible.
NOTE: Use extreme care when grinding a rust-
out. Because rust deteriorates a panel until it is
very thin and weak, excessive pressure with the
grinder can burn a hole right through the metal.
Always wear safety glasses or goggles when
grinding.
3. Use a hammer or tin snips to break away the
softened metal around the rustout. Hammer down
the edges of the hole slightly to bevel them.
4. Use a hand sander or a #50 grit rigid sanding
disc to remove surface rust. A wire brush or die
grinding attachment is ideal for cleaning out pitted
areas.
5. Apply metal conditioner or a rust deactivator
to the repair area to neutralize any remaining rust,
particularly along the edges and in the pits.
6. After cleaning the backside with a wire brush
or scraper, apply a rust deactivator. A solid black
coating should develop. If the color is splotchy
and uneven, apply additional coats of rust deactivator, waiting one to two hours between coats.
WARNING: If any excess rust deactivator runs
onto the car's finish, wipe It off Immediately using
a cloth dampened with white mineral spirits.
Applying the Patch
1. Cut a piece of fiberglass cloth approximately
2" larger than the hole. Cut a similar piece of plastic film, or release paper, approximately 4" larger
than the hole.
2. If a stronger patch is desired, make a laminate
by cutting additional layers of fiberglass cloth.
Each additional layer should be 1/2" smaller than
the preceding one.
3. To provide maximum strength, use either liquid resin or a fiberglass-reinforced filler with long
strands. Prepare the filler as described earlier,
making sure it is mixed thoroughly before
applying.
4. Spread a thin coat of filler on the repair area
and on the piece of plastic.
5. Place the fiberglass cloth on top of the filler-
covered piece of plastic. If additional layers are being used, set the smallest one on first, the next
largest, and so on; the largest piece is put on last
because it will be the bottom of the patch.
6. Place the patch, fiberglass side down, over
the hole. Use a plastic spreader to smooth out any
wrinkles or high spots in the plastic and press out
all air bubbles.
7. When passing the spreader over the center of
the rustout, press down hard enough to leave a
1/8" to 1/4" indentation. Do not press so hard that
filler is forced out from beneath the patch.
8. Use the spreader to feather the edges of the
patch level with the surrounding metal.
9. Let the patch cure, then remove the plastic.
While the filler is still rubbery, file down any high
spots with a cheese grater.
Completing the Repair
1. Mix enough fiberglass-reinforced filler to fill
the 1/8' to 1/4" indentation in the patch. Use the
spreader to apply the filler evenly and press hard
enough to force out air bubbles. Always work the
spreader from the edges to the center.
NOTE: A smoother application can be achieved
by placing a piece of plastic film over the filler first,
then working the spreader over the plastic.
2. Let the filler dry, then remove the plastic film
(if used). Sand with #50 grit sandpaper and a sanding block to within 1/16" of the finish.
3. Switch to #80 grit sandpaper and sand down
to the finish. Do not over-sand this will only create
low spots that require additional filler.
4. Feather the edges of the filler level with the
surrounding surfaces.
5. Wipe the repair area with a tack cloth and use
compressed air to remove any excess dust particles. Spray with primer.
6. When the primer has completely dried, coat
the repair with glazing putty. Use a clear rubber
squeegee to apply the putty in smooth strokes.
7. When the putty has completely dried, use
#240 grit sandpaper and a sanding block to
smooth the glazed surface. Fill any remaining pin-
holes or voids with putty, then sand again.
8. Wet sand lightly with #400 grit sandpaper to
remove any sanding scratches.
9. Clean with a tack cloth, then prime the repair
area again. When the primer has dried, the repair
is ready to be painted.
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