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Chapter 8 Nonstructural Panel Repair
the filler as soon as it is mixed. Once the mixed filler has
cured too much, it is not workable.
C A U T I O N
Never return mixed filler to the can. The mixed filler will
contaminate the unmixed filler.
Use a clean spreader to apply a thin coat of mixed filler
to the low area. Press down hard on the filler as the first
coat is applied. This will squeeze out the air from under
the filler and reduce the number of pinholes. Pinholes are
pockets or voids in cured filler. Apply additional coats of
filler, building up the filler until an overfill (filler higher than
the surrounding metal) is achieved. After overfilling the
low area, use light strokes with the spreader on the filler
to obtain a smooth surface. Stop working the filler when
it begins to stiffen. Allow the filler to cure. Shop tempera-
tures below 60°F increase cure time. Clean the mixing
equipment while the filler is curing.
Filling a body line can be difficult. A simple body line
can be filled by spreading an overfill on the peak of the
body line. A complex body line can be repaired by forming
the filler to match the contour of the undamaged body line.
A contour sander can be used to mold the filler. Put 2"
(50 mm) masking tape over the contour sander that best
matches the shape of the original body line. Apply the
mixed body filler to the damaged body line and press the
body filler into the proper shape with the contour sander.
Hold or tape the contour sander in place until the filler
hardens. When the filler has hardened, remove the sander.
The filler should be shaped so it requires little sanding.
Most problems are caused by the filler or hardener
itself, the mixing procedure, or the condition of the appli-
cation site. To avoid problems, follow these guidelines:
Check the manufacturer’s date on the filler can.
If the filler is over one year old, do not use it. This
rule applies even if the can is unopened.
If runny liquid hardener comes out of the tube after
kneading, do not use the hardener.
If the metal is below 70°F, warm the metal with a
heat lamp before applying the filler.
If the metal is damp, use a heat lamp to warm and
dry the metal before applying the filler.
Follow the recommended mixing procedures. Too
much hardener, which is evidenced by a deeply
colored mixed filler, will cause pinholes and a
lack of adhesion. Too little hardener will cause an
insufficient cure (soft filler) and a lack of adhesion.
If the filler is to be applied over bare metal, use a
grinder or 80-grit sandpaper to remove the paint.
This procedure will abrade the surface, allowing
the filler to bind to the rough surface.
Some manufacturers recommend that filler be
applied over epoxy primer. The bare metal is
sprayed with epoxy primer. Once the epoxy primer
cures, it is scuffed and the filler is applied. Check
the paint manufacturer’s recommended cure time.
It may be as long as 24 hours.
The application site should be ground or sanded
and then cleaned to remove oil, wax, or any other
surface contamination.
The initial removal of excess filler is not really a sanding
operation. When the filler has hardened to the consistency
of processed cheese, a surform tool, commonly called a
cheese grater, is dragged across the surface. The cheese
grater, shown in Figure 8-55, works like a file to remove
excess filler. Grating is a fast way to remove filler. It is faster
than most sanding operations. However, do not grate the
filler too soon. You must allow the filler to cure long enough
to adhere to the metal. Grating too early will pull the filler
off from around the edges of the repair. The ragged edges
will require additional filler. If tack-free filler is used, grating
is not required. Allowing the filler to harden completely and
then sanding is an acceptable alternative.
Fully cured filler is sanded starting with 40-grit paper,
followed by 80-grit paper and then 180-grit paper. On
small areas that the sanding tool can span, start with
80-grit paper. Sanding before the filler is fully cured will
clog the sandpaper with sticky filler residue. The filler can
be tested for full cure by scratching it with a fingernail. If the
filler feels soft, moist, or sticky, it is not ready for sanding.
If the filler feels dry and hard, it is ready for sanding. The
sanding process will level and featheredge the filler. Do
not prime the filler for at least ninety minutes after it is
applied. Solvents will evaporate from the filler even after
it has cured. It takes ninety minutes for all the solvents to
completely evaporate from the filler.
Filler
Hardener
Figure 8-54. Body filler and hardener are combined on
a mixing board.