Automotive Bodywork and Rust Repair

by Matt Joseph

  happen, and the only productive

  thing to do about them is to solve

  the problems that they bring and to

  move on, resolving to learn from

  them and to avoid them in the

  This is the underside of the weld. It isn’t pretty, but it will never be seen.

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  future. In this case, the correction

  A little time spent leveling the area improves its appearance. Then, it will

  was relatively simple.

  have to be protected from corrosion.

  Grinding the Weld Beads and Shrinking the Bulged Area

  While the underside of this weld

  accept paint uniformly, and that no

  Next we attended to correcting

  will not be visible in use, it is an issue

  features that could trap water and

  the bulge that the welding had cre-

  of craftsmanship to give it a neat

  debris were left there to initiate or to

  ated in the short patch and fender

  appearance. On fenders configured

  encourage corrosion.

  metal. A couple of applications of

  with their undersides more visible in

  this area, a more finished appearance

  Leveling was

  1

  would be mandatory. Here, the issue

  accomplished with

  is one of choice—how far do you

  a 4-inch air disc grinder.

  want to take the job? We opted for a

  Its small size and consid-

  neat but not-so-finished appearance.

  erable speed make it

  Our priorities were to leave the

  ideal for this job. It is easy

  underside of the repair area clean

  to maneuver, and small

  and sound for coating with various

  enough to work around

  anti-corrosion treatments like etch-

  intricate features, without

  ing primer, resilient paint, and

  accidentally grinding

  undercoating. It was important that

  them.

  the area be left smooth enough to

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  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

  M I NOR R UST R E PAI R TO A F E N DE R E D G E

  After grinding, and some other abrasive stripping work, the underside of

  2

  the welded area is ready for anti-corrosion treatments. Unseen areas,

  like this one, do not require much finishing and remain stronger if they are not

  Excessive heat in the over-

  3

  leveled too extensively.

  welded area created a bulge in

  the patch and fender metal. This area

  was brought to cherry red with an

  oxy-acetylene torch, and hammered

  down in two operations that shrunk

  the metal, and relieved the bulge.

  shrinking technique resolved the

  bulge problem completely.

  The shrinking technique, in this

  case, involved heating the most dis-

  torted part of the bulge with an oxy-

  While the metal in the bulged

  A final step in the shrinking

  acetylene torch to a temperature

  4

  5

  area was still hot, it was

  process was to quench the

  between dull and cherry red. The

  worked with a hammer-off-dolly

  heated area with a wet sponge. This

  area heated this way was a little

  technique to push the bulge farther

  produced controlled shrinking action.

  larger than 1 inch in diameter. This

  down and to raise sunken areas

  Knowing exactly when and where to

  caused further local bulging. The

  around it. A low-crown hammer was

  apply the quenching action requires

  torch was then safely stowed, and

  used.

  some experience with this procedure.

  the heated, bulged area was ham-

  mered down without any backing.

  This created an upset, literally a com-

  pacting of metal in a small area that

  exchanges lateral dimension for a

  locally thickened panel area.

  The second shrinking operation

  was performed at a lower heat (dull

  red) and over a slightly wider area.

  A check with a straightedge

  6

  indicated that the shrinking

  operation was successful, and that

  the metal in the formerly bulged area

  was now within the range required

  for a good final result.

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  125

  CHAPTE R 12

  A little bowing in one area of

  7

  the outer edges of the long

  repair patch needed to be shrunk.

  That area was heated to dull red with

  an oxy-acetylene torch.

  This time, the hammering was done

  off-dolly, and the dolly rebound

  under the fender was used to raise

  some sunken metal around the

  bulge.

  In this application, the metal in

  After heating, the

  the formerly bulged area was

  8

  bowed area was

  quenched with a wet sponge to

  hammered down, off-

  enhance and control the extent of

  dolly, to upset the

  the shrinking. The area was checked

  metal there. That

  with a straightedge.

  means exchanging

  Measuring indicated that the

  some of its lateral

  bulge had been completely elimi-

  dimension for

  nated, and that the area now had

  thickness, which

  the correct shape. Some distortion

  amounts to compact-

  in the fender-edge repair patch

  ing, or shrinking, its

  metal was now removed by heating

  surface area.

  and hammering that area, gently,

  off-dolly.

  Final Steps before Filling

  The weld beads were now leveled

  visible corrosion was removed. This

  to the fender by grinding, disc sand-

  operation was left until now because

  ing, and filing them almost level

  welding tends to create scale and

  with the surrounding metal. In the

  debris that have to be removed

  battle to level welds, it is fair to use

  before filling. Final cleaning after

  any tool or device that helps do the

  welding is the best approach, since

  job. In this case, we even used a rat-

  removing every trace of contamina-

  tail file and a die grinder.

  tion from the entire area before

  After leveling the weld beads, the

  welding it would be a waste of time;

  surface was inspected. No low or

  it would just have to be done again.

  high spots were found that were

  The nylon disc-stripping wheel is

  beyond the range of modest filling

  a particularly useful tool for getting

  and filing. A few low areas were

  into the surface intricacies of metal

  raised slightly with a pick hammer,

  and removing lightly pitted contam-

  completing the metal finishing of

  ination

  from

&
nbsp; them.

  Following

  Various grinding and disc

  1

  the repair area.

  mechanical cleaning, the repair area

  sanding procedures were then

  The topside of the repair area was

  was wiped down with solvent and

  applied to the surfaces in the repair

  now

  completely

  cleaned

  and

  blown dry. This was repeated until

  area to clean, level, and prepare them

  stripped to bare, healthy metal. All

  the wiping rags came up clean.

  for the next step: filling with body lead.

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  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

  M I NOR R UST R E PAI R TO A F E N DE R E D G E

  Final leveling of some of the welds, in some areas,

  A high-speed, air-driven, right-angle die grinder was

  2

  3

  required a variety of approaches. Good, old

  particularly helpful for leveling some weld areas like

  fashioned filing with a rat-tail file is very useful for some

  the one shown here. This tool cuts quickly and accurately,

  of this work.

  and is easy to control.

  At this

  4

  point, it was

  important to clean

  the entire repair

  area for the next

  steps, tinning and

  leading. Rotary

  and hand wire

  brushes, and other

  devices, sped this

  job, as did the

  Before moving on to the next

  5

  grinder-mounted

  step (tinning), the entire repair

  nylon/carbide

  area was wiped down with solvent,

  wheel, shown here.

  and blown clean and dry. This

  procedure removed abrasive and

  chemical residues from the surface.

  Tinning

  We decided to fill the repair area

  Tinning

  1

  with body lead to correct any low

  compound

  spots, and to allow us to file the sur-

  was dripped onto

  face to exactly the contours that

  torch-heated

  would make the repair area indistin-

  metal in the repair

  guishable from the rest of the fender.

  area. The heat

  The first step was to tin the area

  was supplied by

  to be leaded. It was pre-heated with

  an air-acetylene

  an air-acetylene torch to about 300

  torch, and held to

  degrees F. Tinning solution was then

  roughly 300 to

  dripped onto it from a plastic squeeze

  350 degrees F. The air-acetylene torch produces much milder heat than the

  container. At these temperatures,

  oxy-acetylene torch, previously used for the shrinking operations.

  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

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  CHAPTE R 12

  The tinning compound was brushed around on the

  The 50/50 (tin/lead) solder was then unspooled

  2

  3

  hot metal with an acid brush, while more heat was

  from a coil and melted onto the surface. The torch

  applied to it. A visible, brown residue formed on the metal.

  was played over the area to keep the base metal hot

  This was a good indication that the tinning compound is

  enough for the solder to melt and flow onto it.

  doing its cleaning job.

  tinning solution chemically cleans

  spread it evenly across the surface.

  base metal, preparing it to accept and

  During this operation, the air-acety-

  adhere to tinning solder. As the tin-

  lene flame was played on the surface

  ning solution hit the panel metal, it

  to keep it hot enough to maintain

  sizzled on the hot surface, leaving a

  the solder in its liquid form.

  brownish film. That is the proper

  A few spots that resisted the sol-

  appearance for the application of this

  der’s flow and adhesion received

  product.

  small additional applications of tin-

  While in a liquid state, the

  4

  Next, 50/50 (tin/lead) solder was

  ning flux. Then, the solder was

  solder was spread on the metal

  uncoiled from a spool and run onto

  brushed into them with a small

  surface with a rag. The tinning solder

  the metal’s surface, as the air-

  stainless-steel-bristled brush. This

  must fully cover the metal. However,

  acetylene flame was played over it to

  worked, completing the tinning

  rubbing it too hard with the rag may

  keep it hot. After sufficient solder

  process. The whole area to be leaded

  wipe it away completely, resulting in

  had been deposited on the entire

  was now covered with a uniform

  spotty bonding of the lead filler

  area to be tinned, a rag was used to

  coating of tinning solder.

  material.

  Applying the Lead Filler

  The most outstanding character-

  Lead from a

  1

  istic of autobody lead—the one that

  30/70 body

  makes it ideal for filling depressions

  solder bar was then

  in metal work, while providing a

  stubbed onto the

  medium for filing contours—is that

  tinned surface. The

  it is a metal applied to a metal. With

  end of the bar, and the

  correct

  application,

  the

  bond

  metal around it, were

  achieved with the metal substrate is

  heated until the lead

  unequalled by that of any other type

  started to soften. Then,

  of filler. However, paddling lead

  a lead stub was

  onto a properly tinned surface is

  twisted off the heated

  about as difficult as making water

  end of the bar, and

  run uphill.

  onto the panel surface.

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  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

  M I NOR R UST R E PAI R TO A F E N DE R E D G E

  The lead

  2

  was

  softened to a

  plastic, bubble

  gum-like,

  consistency with

  the end of the

  torch flame, and

  spread on the

  repair area

  surface with a

  lubricated maple paddle. The lead application must be as even as possible,

  and generous enough to allow filing it to final contours.

  Our first step was to stub a 30/70

  putty knife. While the filler looks

  (tin/lead) body solder bar onto the

  somewhat rough, it was easy to file it

  tinned surface. This was done by

  into a smooth and accurate surface.

  heating the end of the body solder

  At this point, we killed the lead.

  bar, while playing the end of the air-

  That term describes neutralizing

  acetylene flame over it and the

  chemica
l residues from the flux used

  tinned surface. The lead material has

  in tinning, and from the lubricant

  a plastic state at between 100 and

  used to keep the maple leading pad-

  150 degrees F, depending on its com-

  dle from sticking to the lead. While

  position. In this peanut-butter-like

  the killing process will be repeated on

  state, it can be twisted off in short

  the panel after it is filed to its final

  These two photographs show

  3

  stubs, onto the tinned surface.

  format, as the last step in leading, it is

  the repair area surface after

  After

  enough

  stubs

  were

  also critical to do this before any fil-

  the lead application was complete.

  deposited, we spread them into a con-

  ing is done. Otherwise, residues will

  The apparent roughness of the

  sistent layer of filler with a lubricated

  be filed into the lead and it will be

  surface is not a problem, because

  maple paddle, much as you might

  difficult, or impossible, to fully neu-

  body lead is a soft material and files

  spread peanut butter with a small

  tralize the finished surface.

  easily into desired contours.

  The panel surface was wiped as clean as

  4

  possible, and treated with metal conditioner. This

  After the metal conditioner had reacted with the

  5

  step was repeated after filing and sanding were

  metal in the repair area for a few minutes, it was

  completed, but it is important to do it at this stage, to

  wiped off. This step, and its repetition when the surface is

  avoid filing contaminants into the filler, making them

  completely contoured, prevents the loss of paint adhesion

  harder to remove later.

  that can occur if these steps are omitted.

  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

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  CHAPTE R 12

  Shaping the Lead and Finishing the Job

  Filing lead filler is not very dif-

  ous. Some filing was solely in the

  what soft rubber backings behind

  ferent from grating and shaping plas-

  lead filler material. In other areas of

  the abrasive paper, and tend to fur-

  tic filler, except that different tools

  the repair, lead and steel panels were

  ther average and blend the surfaces

  are used to do it and the shaping

  filed and blended into a continuous

  on which they are used. Paint sticks,

  operation feels very different. We

  surface. Care was taken not to file

  wrapped in abrasive paper and with-

  began shaping the lead with a bull-