AO Platinum Member
Join Date: Feb 2002
Location: The land that Time forgot
Alfa galvanised most of the panels on the GTV but the floorpan for some reason didn't get treated. 155 and 145/6 of the same vintage are exactly the same.
The floorpan will probably be rusting all the way along the inside joint with the sill.. and possibly at the rear trailing edge of the footwells. There is also a rust trap just behind the front wheel arch.
Alfa's of that era have a thick rubbery mastic goo applied to the underside.. It's pretty good.. but anywhere where it covers a corner, or a joint (such as that pressed and welded seam where the floorpan joins the sill) the mastic eventually becomes more brittle and eventually splits.. allowing water to get in.
That water rusts the ungalvansed floorpan, which lifts the mastic and thereby allows more water to penetrate. You can only see the full horror of what's gone on when you peel off the (now) loose mastic.
You should remove the sill covers to be able to see what's going on. Get a big screwdriver and use that to lift off the loose mastic and rust. I'd also suggest using a small hammer to tap the screwdriver like a chisel, as if you were sculpting.. it makes any scabby bits of metal fall off.
If you penetrate into the car with the screwdriver, you need to get the metal welded.
In any event, you have to remove as much of the mastic and paint and seam sealer that you need to, until you see fresh metal. The mastic sticks pretty hard.. so if any lifts off, the metal underneath is rusted. If you can't lift it or pull it off the surface, then you're good.
Clean up the rusted metal between the good areas with a wire brush and the screwdriver/chisel method until you have just smooth/thin rust exposed.
The more rust you remove the better.. a wire brush attachment to a drill will make it easier.. but if you have a sanding disk, that would be good too. If you tap the rust and hear a "metal" clang then that's fine. if it's crunchy.. then it's rust.
Treat the rust with Rust killer. Bilt Hamber do some excellent treatments but the Big H. sells Kur-rust which is also half-way decent.
Then (when it's cured) you have to seal the converted rust in. Use something like smooth Hammerite since it forms a skin over the rust. You don't need an aerosol... just brush it on.
After that, when it's dry, you can apply something thicker over it, like Waxoyl underseal.... so that you have several different layers of protection on it as thick as the original protection was (i.e. when the repaired section reaches the height of the good areas).
If you find a hole, particularly at the floor-sills joint, then you should weld more metal over the top of it. If you've cleared the paint, mastic and old rust off until you get to good metal (you can't weld metal onto rust), that makes the welder's job easier (they hate all the preparation..)
You will have to take the carpet out since the welding will melt it otherwise and you may have to shift some wiring and possibly the seats. It's why rust is the biggest killer of cars.. the effort to resolve it is way higher than for any mechanical issue.
Personally I'd get the lad to weld on a sheet of galvanised or even stainless steel (why not?) since this is all that's holding your floor to the sill and you don't want to be doing it again next year or the year after, I reckon..
Welding shops tend to have some high-build underseal stuff that they'll spray about 5mm thick over the repair.. so it's pretty much done forever once they've welded it. Before you reassemble the beast treat and paint the inside of the repair (inside the car) so that it can't rust again from the inside out. Finish off with some waxoyl poured into any seams or joints so it blocks out any way for water to get in.
Re-create any drain holes, if you've blocked them off, or you could end up with puddles inside the car (though I've never had any water inside the car.. so I dunno what those little vent/drains are actually for, apart from being a rust magnet.. )
No bullets for Chaingun..
Last edited by Ralf S.; 24-08-11 at 13:55.