Repairing Rust the Right Way.
More than likely you're going to have to fix some rust at
some point. If you live in the northern states it's
In repairing rust you're gonna need a welder. There's
only one way to fix it, and that's cut out the rust and
weld in good metal. To begin welding, a MIG welder is
your best friend. Get a decent one with a gas bottle.
You will thank me.
Ok, how bad's the rust? We will assume you read the
Wisdom section and got a decent (fairly solid) vehicle.
So hopefully it's not that bad. If you are fairly new to
welding, then start with the floor. It will be hidden
and unless it's too severely rusted won't be structural.
If it is, then practice welding before you even start.
There are usually two kinds of welds you will do in
bodywork. There are plug welds and solid butt welds.
Plug welds usually attach one structure to another
structure. Like a floor pan to the floor support. Or an
inner fenderwell to a quarter panel.
Solid butt welds attach metal within the structure. Like
fixing a hole in a floorpan or welding up a hole in the
Say you're fixing rust in the floor and it extends over a
floor support. You will solid weld new metal in the floor
where you cut out the rust, then plug weld the floor back
to the support.
When you plug weld, you're replacing the spot welds the
factory put in. Since most people don't have a big spot
welding attachment, we plug weld.
To plug weld, first make sure to coat the metal parts
where they will be in contact with each other with weld
through coating. You can get it in a spray can. Once you
plug weld the parts together, you won't be able to coat
inside that seam. Never leave any metal uncoated! Then
drill or punch about a 1/4 inch hole in the upper piece
so you can weld to the other metal piece below. First
hold the two pieces tightly together with clamps or
pressure. Then using a slow circular motion with the
welder, you fill in the hole.
To butt weld, you have to get the two pieces to match
exactly. We'll cover that in a minute. Then, using tack
welds, tack the two pieces together. Spread the tacks
around the piece you are welding in. Align the two pieces
and tack, align and tack, etc. until they're a couple of
inches apart. Spread the work around so you don't heat
one area too much and warp the metal. Remember, don't
rush it. Let things cool down some before doing more
tacks. Once it's tacked in, weld short stitch welds
between the tacks about an inch long. Again, move around
the piece so you don't heat one area too much. Some
people prefer to simply keep adding more tacks until the
seam is filled to keep from warping on a big flat area.
Ok, let's fix some stuff...
First, decide if you just need to replace an area, or
replace the panel. Sometimes it's less work to weld in a
new panel than to fix five different places in that
panel. Is most of the panel solid? Is there good solid
metal all around the rust area? If so we'll cut out the
Get your grinder and grind away the paint down to bare
metal along the lines where you want to cut the rust out.
Be careful not to grind away the metal.
Try to get a flexible ruler of some sort (or the straight
edge of a piece of thin cardboard) and mark out some cut
lines with a marker around the rust area being sure to
get into good metal. Straight lines make it easier to
make a new patch.
Cut out the area with tin snips, a cut-off wheel, jigsaw,
or anything else you need to make a nice clean cut.
Now, using some flexible cardboard hold it behind the
cutout and mark the line you just cut. If you can't get
behind the piece, hold the cardboard against the cutout
and push against the cut lines with something hard to
indent the cardboard. Now you can see lines to cut out
Transfer your pattern to some good metal. Make sure it's
about the same thickness. You can use a replacement
panel, new metal, or simply cut out good metal from an
old hood or junk panel. It will be the perfect thickness
and it's cheap!
Now trim out the patch you just drew cutting about 1/2
inch outside the line. You want it to be a little big
since you still have to shape it and trim it to fit.
Shape the patch to fit the area you cut out. We'll cover
metal shaping more in another chapter.
After you have the shape, start to slowly trim the patch
to fit perfectly. The better it fits, the easier it will
Now make sure all edges on both pieces are clean to bare
metal back about 1/2 inch. Make sure if you can't get to
the back of the part after welding that you coat the
backside of it now.
Now hold it in place nice and flush so you can tack it.
Magnets work well. Align the piece and tack as you go.
Now weld that sucker in.
Now take your grinder and carefully grind down the weld
that you made being careful not to get into the
surrounding metal. Don't get it smooth, just close. If
you can, do it on the backside too. Finish up with 80
grit to finish smoothing it being careful not to grind
into the metal making it thin. You just want to get the
weld even with the rest of the metal.
Now coat it with some sealer/primer so it won't rust, and
you're finished with repairing rust!
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