The traditional way to repair a panel is set out with excellent illustrations in the workshop manual: it involved oxy-acetylene welding with loads of heat damping to prevent distortion but probably also a seven-year apprenticeship! Then along came Mig welding that was easier for amateurs to use and avoided the need to store large gas bottles. But there was still the heat problem, not only from the risk of distortion but also the fact (confirmed to me by someone with the right qualifications) that if you heat metal to welding temperatures, you make it more susceptible to corrosion.
If there is a way of avoiding these problems that is practical, durable and within the scope of the amateur restorer, then I think we have to consider it. If it reduces distortion, it also avoids having too much filler on the outer surface of the panel. I have researched other opinions and the majority are very much in favour. The minority are against, viewing it as the latest version of pop-rivets, alloy sheet and Isopon (Bondo). What convinced me was that it is being used now by manufacturers as a standard approach to car production and in other industries.
The rusty section of the panel is cut out as before and cleaned up to a bare metal surface along the joining edges. The repair panel is trimmed to fit and the edges to be joined are then “joddled” (or “joggled”), which means a strip of metal about 20mm wide is depressed using a special joddling tool, so they can be fitted to another piece of sheet metal flush with the main surface, but concealing the overlap. This makes for a strong joint and reduces the need for filler.
The bare metal edges to be joined must be properly prepared to take the glue. This is very important. They must be totally free of grease, oil and corrosion and the glue manufacturers also supply a product for this purpose. The glue is applied to the joddle and the repair panel fitted. The repair panel needs to be clamped, or in awkward situations small self-tapping screws could be used to secure it and the heads ground off afterwards. When the glue has cured after about four hour hours, the outer joint line that is on show can be filled and repainted in the normal way. The glue itself seals the seam inside as long as you make sure it covers all the bare metal.
The materials should be available from any factor that sells auto paint and there are also on-line sources. The products that I have found are:
3m Structural Adhesive – a two pack system that requires a special double gun that mixes the two components as it dispenses them.
Bond Tech – also two-pack with matching dispenser.
Eastwood offer a kit but this includes tools and other items that you may already have.
For a demonstration publicity video by 3m, click here.
This is Trevor Jones original post that aroused my interest (29.02.2012):
"I have just finished repairing the doors of the Magnette. I have tried various methods for the lower repairs to the door skins. The frames are fairly simple and just need time as they tend to be best repaired by welding in small sections, which prevents distortion and ensures the shape is retained. The skin repair I have tried on "scrap doors" (not Magnette) to find the best method. Welding, even slowly tack welding and using wet cloths to absorb the heat, lead to distortion. This lead me down the route of using adhesives and, I have to say, the results are stunning: no distortion and very strong repair.
The biggest problem to be aware of is that, when the skin is cut, the original remaining door skin will sag. I used John Shorten’s repair sections and trimmed them to suit the repair with a joddled flanged edge. Cleaned all the surfaces, roughed up the surfaces and applied the adhesive to the repair panel joddled edge and also to the door frame where the repair panel fits. Using some small simple screw jacks(turn buckles I made from 6 nuts welded together and a suitable length of studding/long bolt) I jacked the original skin back to its correct alignment and shape. Simply leave the adhesive to harden. Once set ,the frame flanges are turned and hammered flat: job done.
I used Bond Tech adhesive on www.bondtech.uk.com and it cost £35: Brilliant.."
My thanks to Trevor for proof-reading this piece to make sure it was right. If anyone else has personal experience of this method, please add your comment below.