Alan:
I dealt with a similar problem on my Midget earlier this year: what I
had thought was only a small hole turned out to be a series of holes that
took up 3/4 of the footwell floorpan. I ended up cutting out the center
section (leaving a 2" inch lip) and riveting in a piece of aluminum.
Later, when I have more time and money, I'll replace the floorpan with a
welded-in piece.
If the rust holes are only small, like 3/8 to 1/2 inches, you can
probably get by with cleaning and prepping both sides thoroughly, putting
a piece of metal tape over the hole on the inside, and undercoating the
backside. This presumes you plan on making a permanent repair sometime
in the future (although, I did this to an old Chevelle once and it lasted
over three years).
If the hole is larger, cut out the bad area and patch it with aluminum or
thin guage steel. You should be able to come up with odds and ends of
either material simply by contacting a local semi-trailer repair shop, or
you can go the junk yard, buy a beat-up hood and take what you need from
it. I used a reciprocating saw (Sawz-All) with a fine metal blade to do
my cutting.
To prepare the area, first clean all the rust off using coarse then fine
wire wheels (do both sides). Cut out the bad section. Wire wheel it
again, as the vibrations from the saw tend to shake more rust loose.
Treat the area with your favorite rust converter (I used Extend and did
both sides). Figure out the size of the patch, and cut, bend, and
conform it to fit over the hole on the *inside* of the car with about a
1/2 inch overlap . Make sure you leave a large lip in the floorpan that
you can later weld to. Position the patch over the hole and drill two
holes, one at each end of the patch. Don't drill into your exhaust,
wiring, or hydraulics (a good tip is to place a thin piece of plywood on
the bottom side of the floor board over the exhaust pipe holding it in
place with a floor jack; when you drill into the wood through the floor
pan, you'll see wood shaving come up the bit and know that you've gone
far enough).
Install a rivet in each of the holes, and check the fit of the patch,
hammer adjusting as necessary. Drill the remainder of the holes for your
rivets, keeping them about 1.5 inches apart. When you're through
drilling the holes, drill out the two rivets you installed earlier.
Reapply rust treatment to the edges and area surrounding the hole you cut
out earlier, and the holes you just drilled, making sure that you touch
up any scratched areas (do both sides). Once it is dry, place a piece of
cardboard over the inside of the hole and spray the bottom side with
rubberized undercoating (hang something over the exhaust to avoid getting
overspray on it). Remove the cardboard, spread newspapers under your
car, and spray the inside area and around the hole from the topside.
Spray both sides of the patch, then let everything dry.
Once dry, use a good sealing/caulking compound to make a gasket around
the hole on the inside; I used a polyurethane roofing joint/splash apron
sealer. Make one bead around the inside of the hole, and another where
the edge of the patch panel will set. Place the patch in place over the
hole and align the holes you drilled. Dip the head of each rivet in the
sealing compound, and install the rivets working side-to-side,
inside-to-outside.
When the last rivet is in place, smear the compound into place on both
sides of the floor pan, adding more as is necessary. From the bottom
side, make sure that the edges and the heads of the rivets are completely
covered with the sealer; switch to the top side and do the same. When
the sealer has set up, undercoat both sides with a rubberized coating.
Hope this helps!
Rich
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