We are hastily approaching the time of year where we all move indoors – indoors to the confines of our workshops and garages, to initiate the list of winter projects which our beloved classics have accumulated. I too have my winter project all lined up. I will be reassembling my old Land Rover. The majority of the project consists of cleaning old parts and putting it all back together again. However, there is one obstacle on the road and it’s called Birmabright.
Birmabright is probably best known as the material used for the Land Rover’s body since its launch in 1948. It was however also used for a few other classic British vehicles, such as the doors, the bonnet and the bootlid of the Rover P4. Towards the end of P4 production, a change was made to ordinary steel in an attempt to cut production costs. An early application of Birmabright in the 1930’s was for the bodywork of the land speed record car, Thunderbolt. Later it was equally used for the bodywork of the Bluebird K7 used for the Coniston record attempt by Donald Campbell. But the biggest applicant of Birmabright was no doubt Land Rover – right up until 1980 where Birmetals, who were producing the aluminium, closed. After this a different type of aluminium was used for subsequent Land Rovers.
Birmabright consisted of between 1% to 7% magnesium, a little manganese and the rest was aluminium. These alloys were available in a variety of temper conditions such a soft, ¼ hard and ½ hard, and were designed to be hardened through cold pressing into shape. Birmabright does not harden through aging. The alloy demonstrates good weldability while its machinability was a lot less impressive.
The body parts of the old Land Rover are directly attached to the steel chassis and to a few simple steel constructions such as the bulkhead or the door supports. This direct contact between Birmabright and steel leads to galvanic corrosion. This is a natural process which occurs when two different metal types are in direct contact through an electrolyte such as saltwater or even just the salt present in normal air humidity. The result is simple – Birmabright will disintegrate with time wherever it is in contact with the steel construction. This phenomenon is especially predominant at holes for bolts and screws. Thankfully, Land Rover also used aluminium rivets to hold several parts together, and in these places the corrosion has remained absent. But where the rivets weren’t suitable or strong enough, Land Rover often reverted to steel nuts and bolts, and in these places the corrosion on my Land Rover is quite apparent.
My question is: What is the best method of rectifying these corroded areas? Some parts will simply be replaced by brand new parts? Other parts can fairly easily be found secondhand in good serviceable condition. But I won’t be able to dodge all repairs like this, and a few questions have accumulated in my mind:
What is the best method of removing the old paint from the Birmabright panels? Rotary steel brushes, grinding and even blasting seems a bit violent on the soft aluminium. Should I consider a chemical paint remover instead?
The weldability of Birmabright is supposedly good, but I have to confess that I just don’t trust my own abilities with a MIG/TIG welder – at least not without some serious practice first. There are also a myriad of modern miracle products available enabling you to solder aluminium together using a solder stick and a small gas burner. This appears to be an easy solution, but will it prove strong enough? And will it look right?
I’ve even heard of people simply gluing old and new body parts together with a panel supporting them on the back and then filling the gap. That, however, is probably taking DIY-pebble-stone-engineering just a tad too far. I’m hoping none of our readers would ever consider that a viable solution?
Once the parts have been repaired, they will need a bit of prep work, a base coat and finally paint. This is apparently also not totally straight forward with Birmabright, as it requires a special type of base coat to ensure proper adhesion for the paint. At that stage, there’s only reassembly left to worry about. Of course, I would prefer to eliminate free travel of electrons between steel and Birmabright, so as to prevent future galvanic corrosion taking place. I presume this can be achieved by preventing direct contact between the two metals? Maybe a thin piece of rubber or similar between the two surfaces? Or could the trusty old roll of speed tape even be sufficient? Do any of our readers have any experience with this?
Last but not least, nickel-plated screws and bolts are presumably the best option for reassembly? It’s awfully tempting to use the pretty ones in stainless steel, but I believe they too will facilitate more corrosion?
That probably sums up this winter’s main challenges in my automotive life. All comments, advice and previous experience from our knowledgeable readers would be of great help to me – thank you!