filling a rust hole

Depends on how long you want it to last. Filling the hole with Isopon paste or whatever might last a year or so. But when rust has penetrated, the surrounding metal - even some way away - will be thin as well, and this will also rust through in a short time. If you want a long lasting repair, it has to be cut out and replaced with new metal, *and* properly rustproofed on the inside as well.

If you want a cheap short term repair, the details of how to will be on the Isopon kit - Halfords etc. Painting instructions will be on the spray can.

It has to be cut out, but not necesarily replaced with metal. Doesn't really make any difference, and fibreglass is probably less likely to rust than a welded plate. Rustproofing the back is very important and probably the main cause of failure of repairs that are quite well done in most respects. Just cover the back in waxoyl followed by some underseal.

It goes something like this:

With apologies to the author of the 'Haynes translation' anonymously (still) going around - and also to the OP whose thread I've mercilessly hijacked.

Tom.

and fibreglass is probably less likely to rust

Quite a lot less likely, I would have thought !

Rob Graham

Grrrrrrrrrrrrrrrrrr.

The most important thing is to rub down to bare metal on the outide and inside edge of the panel, to get rid of all rust for an area considerably larger than the hole itself. This is difficult to achieve with double-skinned sections. If ANY trace of rust or moisture is left, the rust will tend to bounce back. I'd sooner have a fibreglass DIY repair done properly than a typical quick and dirty welding job done by a garage.

Regards George

If that 'repair' is simply plating over rust, then I'd agree. But I don't think this method is much used with external bodywork on cars.

The trouble with just filling the hole is making sure you've got at all the rust. And if the resulting hole is large, you'll have weakened the panel considerably. And the filler will fall out due to flexing - sooner or later.

My concern is that it takes time and dedication to get rid of rust, unless you replace a whole panel of course, as garages would often recommend. Garages can't afford to go the extra mile that you can on a DIY basis.

I use fibreglass to bridge a hole - epoxy preferably, as it sticks better and I've never known it come away. Add metal strips or whatever for strength, and it shouldn't fall out, crack or anything. I only use body filler for the final smoothing.

You should always use welding for a hole anywhere near anything structural.

Regards George

It's often easier to cut out the affected part and a matching bit even from a new panel than to replace the whole thing. But for wheel arches, repair panels are often available.

I'm sure a garage or MOT place wouldn't be bothered - you'll need a bodywork specialist for this.

I agree. I used 'garage' as a general term, to include people who fill a rust hole. Perhaps I should have said "BODYSHOPS can't afford to go the extra mile that you can on a DIY basis." Or at least many people, me included, wouldn't be prepared to pay the bodyshop to spend the time required. We tend to give our time for free, I guess, when it comes to many types of DIY. A real labour of love, especially on something like a total car restoration, where you'd never recoup your personal investment, even if you charged your time at the national minimum wage.

Regards George