300SL Gullwing/Roadster quick tip: Metal Preparation

Restoring Gullwings and Roadsters
Paint refinishing tips from Hahn and Woodward Auto Restoration

Photography from Hahn and Woodward

Hi everyone and welcome to our first 300SL Gullwing/Roadster article for MercedesHeritage. By way of introduction, “we” are Hahn and Woodward Auto Restoration. Located in Harmony, Pennsylvania (about 45 minutes north of Pittsburgh), our shop specializes in investment grade automobile restorations with a particular focus on 300SL Gullwings and Roadsters. As this article is being written (December ‘09) we are actively working on the restoration of a 1957 300SL Roadster and have a 1955 and a 1956 Gullwing waiting “in the queue” The cars have been dismantled and various components are being refurbished but there is a long way to go.

Although our focus will be on the 300 SL Gullwings and Roadster, some of our articles will apply to collector car restoration in general. Such is the case for this first article where we’d like to discuss the fascinating topic of Spray Thermal Metalizing and how we have used it in the restoration of our Gullwings/Roadsters and other vehicles. I know what you’re thinking…..how can we possibly pick a more lame subject for our first article??….but stay with me on this for a second.

More than one of the cars that have come through our shop have had previous bodywork done to them…..and this includes the Gullwings and Roadsters. In some cases, thick slabs of plastic body filler have been used to repair damage and the result is often less than Concours quality and will not last. This is where spray thermal metalizing comes into play.

Arc-Spraying silicone-bronze material to a Gullwing body. The gold areas indicate locations that have already received the material.

“Spray Thermal Metalizing” or “Arcspraying” is a process by which molten particles of metal are atomized and projected upon a surface….in this case automotive bodies and components. Upon contact, the particles flatten onto the surface, freeze and mechanically bond, initially to the roughened surface and then to each other as the coating thickness is increased. As the heat energy in the molten particles is small relative to the size of the sprayed component, the process imparts very little heat to the component resulting in virtually no distortion. The resulting surface can then be ground, sanded, primed and painted. For the Gullwings and Roadsters we use a wire material made of silicone-bronze for the steel panels and aluminum for the aluminum panels. Both of these have proven to be far superior to using lead filler.

The Arc-sprayed material produces a very rough surface. The next step is to grind this surface smooth in preparation for a light coat of polyester filler.

Arcspraying has proven to be an excellent body seam filler. We are able to blend the surface around body seams to match the body contours without the need for plastic fillers. In some cases, the process can be used to repair corroded panels that otherwise would be costly to replace. Even severely pitted metal can be restored in this manner. The sprayed metal fills in the gaps and holes with a new metal surface that does not crack or peal.

We do all of our own metalizing in-house. So far, we are very pleased with the results. Just another way in which not all restorations are alike!

As we move forward with our monthly articles, we welcome your questions, comments and suggestions. So feel free to shoot us a question at info@hahnandwoodward.com