Automotive Bodywork and Rust Repair
Page 31
used to move metal thousandths of
helpful in smoothing out the decklid
highly crowned, modified Proto 1427
an inch. If this technique is applied
surfaces, in areas where very minor
hammer worked well for raising areas
properly and with sensitivity, metal
adjustments were necessary. Shot
of the decklid that it could reach. This
cooperates in seeking its pre-
bags limit metal movement, but are
combination dolly had several
collision format.
very forgiving regarding exact
surfaces that were good for backing
placement.
up off-dolly hammering.
unwanted deformation, as you move
such cases we resorted to stud weld-
metal with impact.
ing to pull out these areas. Working
A few areas of the decklid had
damage out with hammers, pries,
such deep and locked-in small areas
etc., is preferable to stud welding,
of damage, that no amount of clever
but sometimes you run out of con-
tool use allowed us to access them
ventional
bodywork
impact-tool
from the panel’s back side. In two
options. Then, stud welding may be
This rawhide shot mallet was
33 great for leveling some areas of
the decklid in a gentle way. Here, it is
being used against a spoon dolly that
A stud welder was used to pull out a small, but deep, dimple dent that
34
is wedged between the back of the
was inaccessible from the back of the panel. This type of device
panel and its substructure.
resistance welds a copper-plated steel stud to the panel’s surface.
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AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
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necessary. One key to getting good
easily and leave no adverse effects in
continuing to pick up low spots and
results in stud welding is to pull out
the metal. The area of this stud weld
push down high spots. Because this
the damage in controlled steps, and
was disc sanded almost flat, and left
panel had considerable crown in
avoid creating over-pulls.
for final filing and finishing when
every area of its surface, it was possi-
Stud welds are easily clipped off,
the panel leveling was completed.
ble to accomplish the entire job with-
and if they are done right, clean up
The rest of the job consisted of
out having to shrink any metal. This
While stud welders produce
35 fusion welds between studs
and panels, there should be no
permanent damage to the panels.
When pulling out dents with studs, it
Here is the result of the stud
37
is critical to locate the stud(s) in
welding operation. The deep
exactly the right place(s). Sometimes,
A simple slide hammer was
dimple, where the stud was welded,
36
multiple studs are necessary to pull
attached to the stud to pull it,
was now level with the panel. If stud
out defects like creases.
and the metal welded to it, out. The
welding had not been used here,
slide hammer was used
excessive amounts of body filler
incrementally, to avoid over-pulling
would have been necessary to fill the
and stretching the metal.
dimple.
After welding, the stud was cut
38 flush to the panel. The heat
from stud welding anneals panel
metal near the stud. As Herb cut off
the stud, he pulled on it and rocked it
The last step in the stud welding operation was to grind the stud stub
39
slightly, to finely adjust the level of
almost level to the panel. A little of the stud was left for final shaving
the metal around it to the panel.
when the panel was metal finished.
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
147
CHAPTE R 13
Because the stud metal is very soft steel, a body file can level it to the
Using a blunt pick hammer and
40
41
panel, easily. Note the burned ring around the stud weld area. This is
a plastic-clad dolly, Herb went
where the outer rim of the stud welder contacted the panel, and supplied
after the low metal that could be
current in the circuit to the stud.
accessed from the back side of the
panel. Plastic dollies only work for very
We
limited on-dolly situations, but that is
42 discovered
exactly what was called for here.
depressed areas,
where the trunk lid
is because high-crown sheetmetal con-
latching mechanism
ceals minor stretches that are not so
and trim had pushed
large as to affect its basic symmetry.
in the surrounding
Various pick hammers were the
metal. Although we
choice tools for making finer
thought that we had
adjustments to the decklid’s sur-
corrected this
face. Hammering was done lightly,
problem, we found
and interrupted with many inspec-
that it needed more
tions. At this point hammering was
work. We had good
almost entirely off-dolly. For par-
access to hammer
ticularly delicate adjustments, a
this area from the
plastic dolly was used for on-dolly
back, off-dolly.
hammering.
Metal Finishing
Metal finishing is the final stage
job. After metal finishing, the metal
coarse steel wool in the repair area.
in sheetmetal work, before body
workers in body shops turn their
There were two reasons for not
filler is applied to a panel’s surface
finished work over to painters and
cleaning the rust and paint residues
to correct any small remaining
think, or say, “Now, buddy, it’s up
to base metal until this point in the
inaccuracies. In the best situations,
to you.”
restoration. First, it would have been
no body filler is used. Metal finish-
Up to this point, we have done
difficult to use abrasives effectively
ing techniques can only be applied
little more to clean the decklid than
in the depressions and creases in the
following the completion of all of
to chemically remove the paint from
damaged metal. Those gross defects
the major movement of metal in a
it and scuff off the loose rust with
have now been corrected. Second,
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AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
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leaving the panel surface uncleaned
also made it easier to indicate low
and high spots by just dragging a
body file or sanding board over it.
The panel was made level enough
to clean it down to bare metal. This
step was accomplished with a 7-inch
disc sander and an 8-inch rotary
orbital sander. Note that abrasive
blasting was not used to do this.
Any blasting method, or media,
that would remove the pitted rust
from this panel would also tend to
stretch and warp it, unless it was
slowed down to the point that disc
sanding would be faster. Thus far, we
have tried very hard to avoid stretch-
ing or warping this panel.
As work progressed, Herb periodically dragged a body file or sanding
At this point, the decklid’s offi-
1
board over the decklid’s surface, to indicate low and high spots. This is
cial portrait shows the metal basi-
a very effective way to get a visual sense of how a panel is progressing.
cally in place, but in need of many
There are faster ways to
2
remove paint and rust from a
panel than disc sanding it. Some of
them stretch metal and should not
be used. Disc sanding doesn’t
stretch metal, and has the added
advantage of indicating high and low
We used an 8-inch orbital sander, after the disc sander, to get the panel
3
spots, and even correc-ting them to
clean and smooth. The orbital sander was too slow to do the whole
a limited extent.
cleaning job, but it was ideal for use after a disc sander to finish it.
AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
149
CHAPTE R 13
had
to
use
some
inventive
approaches, like a homemade slide-
hammer attachment, to move the
metal for metal finishing. The rest of
the work was mostly very light ham-
mer work, backed by spoons held
against the back of the decklid, and
dollies against its outside, as pick
hammers were used to raise metal.
Pick hammers play a major role in
most metal finishing operations.
Due to the extreme access problems
in this job, they played a more
minor role. You can’t pick metal up
when you don’t have access to swing
a pick hammer.
The decklid still needed many small surface adjustments to make it
When the metal work was com-
4
smooth. Some of this will be done with further metal shaping
pleted, and the panel was ready for
applications, and some will have to be accomplished with filler.
filling, it was given a final cleaning
in the areas that had not come com-
small, local surface adjustments. These
stage, all procedures used to move
pletely clean in previous sanding
involve using processes similar to the
metal are milder and less violent than
operations. Various tools and meth-
ones that we have been using, with
those employed in the roughing out
ods were employed to remove as
the addition of filing and sanding the
and bumping stages that preceded it.
much rust as possible, particularly
panel to achieve finer adjustments to
Given the extreme access prob-
from the pits in areas of the metal
its surface. In the metal finishing
lems to the back of the panel, we
that had been covered by trim.
The tool is inserted through available holes in the
6
This homemade slide-hammer attachment was very
panel. Then, the slide-hammer’s weight is slid up its
5
useful for working through holes in the decklid skin
shaft to provide outward impact against the panel. With
to raise metal. Its contact point can be slid to where it is
this end mounted on it, it has a range of about 31⁄2 inches
needed, and stays there during use.
from the edge of its insertion access.
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AUTOMOTIVE BODY WOR K AN D R UST R E PAI R
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The rest of the metal finishing
7
phase of this job was
accomplished through repeated
Next, it was time to give the panel a final cleaning, before applying
8
applications of the tech-niques used
metal conditioner and body filler to it. A coarse-wire cup brush was used
before, but in finer and finer
to dig rust out of the surface pits in some areas of the panel. Note the old lead
increments as the panel came into
repair below the wire brush.
shape.
Then, the panel surface was
blown free of all loose debris and
wiped down several times with sol-
vent. We ran solvent-soaked towels
and drying towels over it until they
came up unsoiled.
The next and last preparation,
before applying polyester filler to a
few areas of the decklid that needed
filling, was to chemically neutralize
the surface of the panel, and partic-
ularly to treat any remnants of rust
that might have remained trapped
in pits in the metal. To that end, we
diluted a commercial metal-condi-
tioner preparation per its manufac-
turer’s instructions, and scrubbed
into the panel’s surface with a
woven nylon pad and a stainless-
steel-bristled cleaning brush. We
worked sections of the panel,
An old-fashioned, carbon-steel hand wire brush was worked into the
9
roughly 2-feet square, this way, and
pits in the metal with a circular motion. This is a very effective way to dig
then wiped them dry, again, as per
rust out of pits.
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CHAPTE R 13
The
11 panel
was then
vigorously wiped
down with
solvent-soaked
rags, and dried
with clean rags.
This process
was repeated
until the rags
came up clean.
Solvent wipe
down is another small but critical step before filler is applied to a panel.
the metal-conditioner manufacturer’s
cannot be sanded off effectively.
instructions.
Metal conditioner must be applied to
The purpose of applying the
very clean metal; but it is no excuse
metal conditioner was to stabilize
for painting over rust. It neutralizes
the surface of the panel, and to pre-
and stabilizes very minor amounts of
The panel was blown with
vent the clean metal from flash rust-
rust, no more than that.
10 compressed air, to remove all
ing. A good metal conditioner does
Finally, metal conditioner gives
loose rust and debris from it. This
this by depositing a very thin phos-
clean metal tooth, that is, a micro-
small step was absolutely necessary
phate coating on clean metal. It also
scopically craggy surface to mechan-
to get good results in this job.
stabilizes any small amounts of rust
ically interlock and bond with
that remain on the panel, and that
coatings or filler applied over it.
The last step before applying
12 filler was to use metal
conditioner on the bare panel surface.
The metal conditioner was mixed to
its manufacturers’ specifications, and
applied with a nylon scrubbing pad to
After the metal conditioner sat on the metal for a minute or two, but
13
2-foot-square panel areas. In pitted
before it could dry completely, it was wiped dry with clean rags. These
areas it was worked in with a
rags did not come up clean, because metal conditioner tends to dissolve some
stainless-steel wire brush.
rust as it neutralizes it.
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Filling
Polyester filler was chosen for
this job. We mixed it thoroughly in
its can before adding hardener to it,
then we mixed the combination to a
uniform consistency. Preparing poly-
ester filler is not difficult, but it is
important to keep things very clean
when you mix and apply it, and to
avoid all contamination to it by
things like oil and debris.
When the filler was completely
mixed, we applied it to the panel
with a squeegee, in slight excess of
the build that we were trying to
achieve. Note: Never apply the poly-
ester filler in thicknesses exceeding
1/8 inch, overall, and it is best to
keep individual applications to less
than 1/16 inch.
Metal or plastic tools can be
2
Unfortunately, some people who
used to mix filler. Aluminum foil
do autobody metal work do not
Polyester filler was mixed in its
is an excellent mixing surface for
1
understand or observe these limits,
can, prior to combining it with
filler. Never mix it on newspaper or
and greatly exceed them. The results
hardener. This often overlooked step
wood. Avoid surfaces that can absorb