Rust Repair Part 2: Repairing small holes
Closing up small holes using a welder is a fairly simple
process provided that the hole is surrounded by solid metal.
Unfortunately, this is usually not the case with pinholes caused
by rust. Small rust holes are often surrounded by metal which has
been significantly thinned by the same rust which caused the hole
in the first place. This brings us to rust repair rule #2 - it is
often difficult to weld small rust holes closed because the
surrounding metal is so thin that burn-throughs are unaviodable.
There are 4 basic techniques which I have successfully used to
repair small holes of various origins. I will describe each method
below. The great part of these methods is that if performed with
care, the repairs are totally invisible from both sides. :-)
However, the tradeoff is that these methods can be very time
consuming. :-(
The first method is what I call the "Goop and Stick" procedure.
What you do is to weld alternatively on each edge of the hole with a
cold torch, allowing time between welds so the metal can cool enough
to prevent a burn-through. After you have made several passes along
all four edges (Gooping), you will be able to bridge across the
middle of the hole (Sticking). What you have created is a mini-
volcano which is then ground down to leave a smooth, flat
surface. Because this method leaves the backside looking ugly
(and sometimes thin), I will usually put a bead on the backside to
complete the weld before grinding away the volcano. I have
repaired holes in excess of 1/2 inch in diameter this way.
The second method for hole repair is using a copper paddle.
This repair is made by having a friend hold a copper paddle against
the hole from the backside. You then weld the hole closed by applying
a bead around the edges until the hole is closed. The copper paddle
supports the weld while it is molten, which prevents it from falling
through. Since the steel won't stick to the copper, you simply pull
the paddle away after the weld has cooled. A word of warning - The
paddle must fit tightly to the back of the hole and must be held
steady! Otherwise, a burn-through will result. Copper welding paddles
can be purchased through welding and restoration supply houses such as
Eastwood. Otherwise, I think you could make one by flattening the end
of a piece of 3/4" copper pipe. However, I have not tried this so I
don't know if it works or not.
The third method is the "Metal Tab" method. What you do is to
cut a small piece of sheet metal slightly larger than the hole. This
piece (tab) is held against the back of the hole (by your assistant)
while you weld the hole closed from the front side only. Go over the
weld if necessary to build up the metal until the entire patch is
thicker than the original metal. The weld is then ground down until
smooth on the front, and the tab is ground off of the back side.
The last method is the plug method. This is best suited for
larger holes or holes which are surrounded by a localized thin
spot. What you do is to drill out the hole to the minimum size
which has solid metal on all sides. A flat washer or steel plug
is then selected which fits tightly into the the hole, and this
plug is welded into place. If using a washer, the center hole can
be welded closed onthe bench prior to welding into place. CAUTION
- NEVER USE GALVANIZED WASHERS! The coatings emit a toxic gas when
welded (very unhealthy!), and the welds come out very brittle and
porous! Also, if you are using a used washer, make darned sure
it is clean from grease, rust, wax, etc, otherwise it will
contaminate the weld. If you use this method, you are best off
using new mild steel washers.
All of these methods are effective for performing repairs, but
all can be time consuming. About a month ago I made a rust repair
(using the metal tab and paddle methods) on the quarter panel of
my brother's convertible. The area was about 2" by 8" and was
surrounded by solid metal, as the rust out was caused by a pile of
debris which had collected in the lower corner between the inner
and outer panels. This repair took a total of about 4 hours to
make mostly because the welds had to be ground on the backside
using a die-grinder (mine is the world's worst) and it took about
6 passes to build up the metal to an adequate thickness. However,
when it was done the patch looked great from both sides and the
metal is thicker than OEM thickness. By comparison, I filled 19
other holes in solid metal (the PO had a sliding hammer dent
puller - boo, hiss!) in about an hour.
Stay tuned! Tommorrow is the last and final part (thank god?!)
on using patch panels.
Adios for now,
Mike "Will he ever stop?" Harlan
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