Newbie in a pickle over BMW 635csi underseal!

[Dave9118]

Hi all, new to this forum and just wanted to get some advice from all you seasoned pro's out there.
I'm renovating a 1986 BMW 635csi which is in overall good condition for its age, with only minor rot in the usual places. The car has been undersealed from new by the looks of things, and has been sealed with something that I can only describe as old chewing gum (unknown). On the face of it, this has done a superb job over the years and kept the underneath solid. The only areas where rust has beaten it are around the sills and the corners of all the wheel arches.

My question is;

1. Do I strip and re-seal the whole of the underside of the car with new wax and stone chip, or just carry out my repairs and touch in where I have removed the coating?

2. There seems to be a real difference of opinion on the best brands of underseal to use, so what is the opinion of forum members on a good long lasting underseal?

Thanks in advance...

[Luxobarge]

Hi, and welcome to the forum.

1. No, I'd strip the old underseal back until you reach pristine metal, then repair from there. Unless you are going for a totally concours car and enjoy stripping old underseal off!

2) In my opinion the traditional black gooey shutz type underseal is the work of the devil and I'd never touch it with a barge-pole. Also, it doesn't actually work very well in my experience. The best results I've had is to strip back to bare metal, repair, then paint in etch primer followed by some tough chassis paint, followed by spray-on stone-chip paint. Some anti-stone-chip paints are better than others, I've had very good results with 3M stuff, and some others that I can't quite recall right now. Stone-chip is much closer to the rubbery stuff that most manufacturers use in the factory too, and that tells you something I think.

Also, applying shutz is a filthy messy job, whereas the preferred method above is nothing like as difficult or messy!

HTH

Cheers!

[Grease Monkey]

I'd recommend Rust Busters 2 pack epoxy, brilliant stuff, available in different colours, but can be over painted.
http://www.rust.co.uk


John.

[Dave9118]

Brilliant, thanks for the replies guys. Glad I don't have to strip all of that underseal off its well on there. I'm going to polly bush it before I put it back together, and was also going to rust proof the inside panels. Can I get away with just primer for this or is there a recommended coating for this too?

I'll post some more pics when I get half a chance

[pryantcc]

Brilliant, thanks for the replies guys. Glad I don't have to strip all of that underseal off its well on there. I'm going to polly bush it before I put it back together, and was also going to rust proof the inside panels. Can I get away with just primer for this or is there a recommended coating for this too?

I'll post some more pics when I get half a chance

Don't just use only primer Dave, most of it is porous and you'll be doing it again in no time! I'd be inclined to use whaterver you're putting uder the car behind the panels too. the tougher and more durable the better in my book!

[Dave9118]

Ok thanks. That makes sense. I'm glad I came on here now. I've been fumbling around in the dark a little bit (and not the good kind). I've done a couple of bikes up and had loads of fun but this is the first car I've attempted. Mechanically I'm ok, and between me and my brother we have most automotive tools you need, but this paint lark is an absolute minefield.

Thanks for the advice!