202 Section 2 Nonstructural Repairs
Copyright Goodheart-Willcox Co., Inc.
bare metal and prepares it for the application of lead.
After the flux is applied, the fill area and the entire bare
metal area are gradually heated. A propane torch or
an oxyacetylene torch with a special tip that burns only
acetylene must be used to heat the metal. The metal is
heated enough that the lead stick softens and adheres
to the panel when touched to the heated metal. If the
metal is too hot, the lead will melt and run off the panel.
Use steel wool or a rag to wipe the excess lead off the
fill area.
After tinning the repair area, the filler can be
applied. Two things must happen during the application
step. The bare metal and fill areas must be kept hot,
but not hot enough to melt off the lead in the tinned
area. At the same time, the lead stick must be heated
enough to soften it. Hold the torch at an angle so it can
heat both the lead stick and the fill area as the lead is
applied to the panel. Lay out enough softened lead to
overfill the fill area.
After applying the lead, the repair must be
smoothed. During this step, the lead filler on the panel
is softened with heat. The softened lead filler is then
spread out and smoothed with a wooden paddle. The
face of the paddle is coated with a layer of tallow or
paddle lubricant to prevent the lead from sticking to the
paddle. To coat the paddle with tallow, heat the face
of the paddle with the torch and touch the face of the
paddle to the surface of the tallow. The hot paddle face
will melt the tallow.
Once the lead filler cools, it can be filed in the
same way as filing high areas when metal finishing.
The lead can be finished by block sanding in the same
way as body filler. Reapplication of lead filler is not
recommended because the existing lead on the panel
will need to be heated and may melt off unless extreme
care is taken. Lead filler can be covered with body filler,
if needed.
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Aluminum Panel Repair
Operations
Some vehicles are made entirely of aluminum.
Other vehicles may have one or more aluminum
panels, such as a deck lid or hood. Aluminum is lighter
than steel. Additionally, aluminum is easier to recycle
than steel. It is anticipated that the use of aluminum
body panels will increase in the future.
Low-crown aluminum panels are the easiest
aluminum panel to repair. Dents are the most commonly
repaired type of damage in an aluminum panel. When
repairing a dent in a low-crown panel, care must be
taken to prevent stretching the panel. Aluminum is softer
than steel. Therefore, hammer-on-dolly straightening
will easily stretch aluminum. Do not use hammer-on-
dolly techniques when straightening aluminum. All metal
panels are work hardened by folds and body lines during
manufacture. Damage adds additional work hardening.
Aluminum can crack due to work hardening; straight-
ening it may cause cracks. Heating the panel during
straightening will minimize the possibility of cracking.
When buckles are released from a damaged steel
panel, the metal tends to return to the undamaged loca-
tion. Aluminum panels do not have this memory. Steel
particles left over on grinder disks, sandpaper, and files
will contaminate bare aluminum. Use dedicated tools
and sandpaper when working on an aluminum panel.
Make the repairs in an area of the shop that is isolated
from the steel repair area. Use a dust extraction system
designed for removing aluminum dust.
Aluminum is much more sensitive to heat than steel;
heat spreads faster through an aluminum panel than a
steel panel. To prevent warpage, power sanders used
on aluminum panels should be equipped with a foam
backing pad. The use of 80-grit (or finer) sandpaper
and disks will prevent excessive removal of aluminum
while sanding. Aluminum does not change color when
heated as steel does. Controlled heat is very beneficial
in repairing aluminum. Do not heat an aluminum panel
to more than 400° F. The adhesive that binds aluminum
parts is weakened by temperatures above 400° F. There-
fore, always check the back side of a panel for adhe-
sives before heating. Avoid heating panels that contain
adhesive. Monitor the temperature of the repair area with
an infared thermometer as the panel is heated. Due to
the shiny surface of bare aluminum, an infared thermom-
eter cannot make an accurate reading of bare aluminum.
Leave the paint on the panel while heating. If the paint
must be removed, apply a piece of masking tape to the
bare area and point the infared thermometer beam at the
masking tape. Heating aluminum above 600° F, called
annealing, permanently weakens the metal by removing
work hardening. Aluminum melts at 1200° F.
When performing shrinking, leveling, or raising
operations on an aluminum panel, the hammer blows
must be softer than those used on steel. Tap lightly. The
faces of hammers and dollies used for aluminum repair
must be free from nicks and gouges. Any irregularities
on the faces of the straightening tools will be transferred
to the aluminum. Some technicians use plastic- or
rawhide-faced hammers to straighten aluminum. Most
body fillers used on steel can also be used on aluminum.
The aluminum panel should be coated with epoxy primer
before applying the filler.