By Jim Kerr
I was working away in the shop last week on my classic Impala project with a couple of friends when the subject of paint came up. I was preparing some of the suspension and underhood parts for their final finish and was sorting them to paint some parts, zinc-coat others, cadmium-plate a few and powder-coat several of them. My reasons for choosing these finishes are the same reason auto manufacturers use a variety of finishes for different applications on your vehicles.
Paint is the standard for most automotive parts. Current paint technology produces long-lasting, high-gloss exterior finishes that are resistant to fading, chipping and even small abrasions. Many of the paints applied to the outside of a vehicle are a base coat/clear coat combination. This process coats the part in a colour coat that may appear dull or flat; then, a clear coat of paint is applied over the base colour to protect the colour and provide a glossy finish. Of course, before any colour is applied to the body, it is first coated with undercoats or primers that help the colour coat stick to the body panels and fill minute imperfections in the metal. Paint is the choice for exterior panels and most underbody parts because it is relatively easy to apply in volume, is reasonably priced (although some paint colours are very expensive) and produces a high quality finish. I will use a base coat/clear coat finish for the exterior panels of my car. The clear coat can be polished to produce an exceptional finish, but no paint will look good if the body work isn’t good, so I have lots of work to do yet.
I have chosen paint for some underhood parts as well. Inner fenders, heater housings and some braces will be painted with a semi-gloss black finish similar to factory finishes, although some customizers will use brighter colours or may even chrome many parts.
Galvanizing is a zinc coating applied to metal to reduce rusting. The coating actually repairs itself from small scratches and is sacrificed over time. Galvanized parts will still rust, but it may take several years for this to happen. Most body panels, with the exception of the roof panel, are now galvanized at the factory by dipping the bare metal body in a huge tank as it goes down the manufacturing line. This isn’t practical for restorations, but I will galvanize many small brackets and special nuts that hold body panels together so they won’t rust. Some will be given an additional coat of paint so they blend in with the semi-gloss black panels.
Cadmium plating is often used to protect parts such as relay covers, electric motor cases and fasteners. To prepare many of the special bolts and washers that are used to hold my Impala together, I have spent hours at the bead blaster, removing rust and grime by blasting each part with glass beads. It leaves a smooth, clean finish that will rust very quickly, but the cadmium plating isn’t expensive and will protect the metal fasteners. Some chrome shops offer cadmium plating, but unless you prep everything first, you will pay for a lot of tedious labour.
Powder coating is very durable. I am having all the suspension, axle and steering components powder coated. There are a wide variety of colours available, but if you want a special colour, you may have to wait for a while before the shop “does a run” of that colour. Metal parts are stripped to bare metal by bead or sand blasting. They are then chemically cleaned of any oil before a dry powder is electrostatically sprayed on the part. The parts then proceed into an oven where they are baked and the powder melts into a smooth durable coating. Because it will withstand chipping, it is ideal for suspension parts, but is too costly for new vehicles. You will find clear powder coating on many factory alloy wheels to protect the aluminum alloy.
Disadvantages of powder coating include cost (slightly higher than paint) and the baking process. No body filler or undercoats can be used to smooth the surface because it will be baked at high temperatures. The powder does flow out to produce a smooth finish, but imperfections in the metal work will still show through. Powder coating is also used on many non-automotive metal products, from patio furniture to lamp fixtures.
The choices for finishing automotive parts are numerous: chrome, paint, powder coating, and specialty finishes such as anodizing are but a few. The factory chooses finishes for three reasons: exterior looks, body rust protection and low cost. The finishes I choose may cost a little more, but I want this classic to look as good when it is 80 as it will at 43 years old.