Help! welding rust holes

[mark_fc]

Hi all,
Unfortunately not much progress has been made on the FC, i have been too busy with school. But now that i have finished my VCE i will have some time to work on it. Anyway i was hoping someone could give me a step by step procedure on how to weld up some rust holes in the rear floor pans. They range from 1mm to 7 or 8mm.

Thanks
Regards Mark

[mcl1959]

Mark, this is a good question and one that people often get a little wrong.
The first thing to do is assess just how bad the WHOLE floor pan is. Rust holes are one thing but the floor pan can also be pitted leaving it a lot thinner in places than it should be and very prone to rusting in the future.
Secondly forget about trying to patch little holes with a welder as you will chase thin metal all over the place and end up with a very messy repair. You must insert a piece of metal to fill a whole well.
You need to start repair patches in good thick unrusted metal and this is why it is generally better to install entire floor pans rather than putting in small patches.

So if you give the floor a really good clean with a wire brush (or even better a wire wheel) and you find that the majority of the floor is pitted with rust then you should replace the whole thing.
The only time I would ever consider small patches is if the majority of the floor (at least 75%) is in good order and rust was confined to just one area.

If you have decided that you are going to install a patch, mark the area with engineers chalk and cut out the floor to the shape required. Place a new piece of metal under the newly cut out hole and scribe its shape onto the metal. This gives you a pattern for the replacement piece and you can cut this out precisely.
Butt welding is better than overlap welding in appearance and is just as strong if done correctly. Overlap welding must be welded both sides and can promote rust if moisture gets between the layers.
If you are going to replace the whole floor pan then just mark out where you need to cut and don't be afraid to trim back the new floor pan if you want to if you find you are just cutting out good steel.

As far as welders go - I prefer OXY but MIG is good as well. Oxy is easier to control in my opinion and the mild steel filler rod is easier to hammer than the MIG filler rod.

Ken

[mark_fc]

Thanks for the help Ken,
I have stripped both floor pans back to bare metal with a wire brush and only found 3 very little holes on the drivers side and a couple of patches on the passengers the rest of the floor pan is still very solid, the drivers side certainly doesn’t need a complete floor pan, but the passengers will need a few small patches. I have read somewhere that you can use a bit of copper pipe to hold behind the hole when you weld it? Does this work?

Thanks
Mark

[simins]

yes placing copper / brass / aluminium plate hard up under the floorpan holes will work while you weld up your small  holes .these plates themselves will not bond to the parent metal of the car. as ken said the larger holes should be cut back to
clean metal and a patch cut to the correct size and butt welded in place.

                       hope this helps Simon Addison