Holes in floorpan MkIII.

[hoytmonger]

Was just under my car and noticed rust stains on the rubber undercoating. I pressed on them and they were soft, so I peeled away the rubber and wire brushed the loose rust out. I now have five small holes in my floorboard, one goes right through to carpet.

What's the best way to repair them from underneath?

[sooperman23]

If the holes are really small you could just use a stick welder and lay down a few beads over the holes and grind it flat (from inside the car). Then just seal it really well and spray some paint and ruberized undercoat. Make sure you get all the rust in the area completely removed. If the holes are really big, there is no way around it. You will have to cut the whole area out and weld in a new panel. I had a golf ball sized hole in my back seat floor in my MK3, and I just did a quick fix because it was the dead of winter and I figured I would fix it right later when I had the time. I removed all the rust in the area. Then I sprayed a primer sealer over the bare metal. Then I took a junk license plate I hade laying around and glued it to the floor using a liberal amount of roofing sealer. Next I screwed 4 short self tapping sheetmetal screws through the plate into the floor. I coated everything in ruberized undercoat (inside the car and underneath). Once it all dried I just put the carpet back. Its been a few years and I still havent gotten to fixing it right, but it has held up perfectly.

[2slogetta]

Your going to have to remove the interior to gain access to your holes. I assume they are quite large if you have 5. Cut them out. You must cut a larger hole than the rust damage. As there will be more that you cannot see. I try to go anywhere from .25-1.0 in larger than the damage. Floor pans have crumple zones. So this task is extra fun. Depending how bad, you may just want to install new pans. I repaired a friends car. I removed and cleaned all dated areas. Then made new pieces to cover my holes. Glued them in from the interior with 3M Panel Bond Adhesive. Very strong stuff. Used to adhere quarter panels and bed sides etc. sheet metal screws to hold the pieces in place. 24 hours later cut the screw points from beneath the vehicle. Seam seal and undercoat everything. Inside, etch prime bare metal, prime and paint. I didn't weld because the heat would have made the repair much bigger.

[deletedo1m]

If I were you I would also give the car a good look over for other possible problem areas especially the strut towers and the gas fill area.

[Bariman82]

Easy answer is to cut out the area back to good metal and weld a new piece in. Here's one I did:


Here's another. This area was the two rubber plugs in the floor of the backseat.


Welds are snotty because they were some of my first. I got better over time (21 patches and two rockers later LOL ) I always just made square or rectangular patches. No one will see it, so there are no rules.