Many of you have written in asking where we are with the '53 Roadmaster restoration. We chose to break up the series for the past few months with other projects while we finished some door jamb detailing and trunk prep on the '53. We are now back on the project and are in the final stages before painting. Our goal for the body is to be factory straight. To achieve this, we are using the guide coat method. Guide coat is applied as a thin coat of contrasting color over the final coat of primer/surfacer. Guide coat is available from several manufacturers: Sem has an aerosol, 3M has a dry powder kit that goes on with a sponge-like applicator, part #05861. These are sold at your automotive paint distributor.
To apply: Put on a dust-coat of contrasting guide coat, allowing the primer to show through. After it dries, sand with a long board and 220 grit sand paper. This will sand away the high spots, leaving guide coat in the low spots. Keep sanding until you are down to the primer/surfacer. If there are still low spots, fill them with primer or filler, depending on how low the low spots are., then repeat the guide coat process (guide coat/sanding/filling, etc.) until you level the surface. After the surface is the way you want it, final-sand with 320 dry. This will leave the metal ready for painting. The reason for using a guide coat product instead of just a can of spray paint, is that the guide coat is compatible with all paints, whereas lacquers or enamels are not. For example, if you spray on enamel, using it as a guide coat, after it is sanded off, just a trace could cause problems if you paint lacquer over it. The two paints are incompatible. It is up to the restorer as to how many times the guide coat process is applied; generally 2-3 times will provide a factory-straight finish. Show car perfectionwould require more repetitions. Watch for a continuation of the series in upcoming issues.
A BRIEF HISTORY OF AUTOMOTIVE PAINT:
In 1923, General Motors along with DuPont, developed a spray painting system using "nitrocellulose lacquer". DuPont had actually been producing lacquer since 1905, but had not applied it for automotive use. This new paint, called "Duco", could not only be sprayed, but had an array of colors. It had to be rubbed, but did not need to be baked. To apply Duco, the body was metal-prepped, primed and sanded, then the color coats were applied, wet-sanded and buffed. These lacquers produced a beautiful, deep finish that was much quicker to apply, and were used until the 1950s. Although beautiful, lacquers had poor resistance to gasoline spills and other chemicals, and had to be rubbed out periodically to remove oxidation caused by the sun and restore the color and gloss.
By the early 1930s, "Alkyd" enamels were developed. These paints were more durable than lacquers, but required baking to make the paint flow and produce a smooth finish. Like lacquer, they oxidized and caused the colors to fade, but overall, they produced a good finish. By the mid-1950s, GM developed a new acrylic lacquer system, which produced a smooth, durable finish that held up better than the old nitrocellulose system. It didn't have the depth of nitrocellulose, but required less maintenance. By the late 1960s, acrylic enamels became available. When used with hardeners, they could be color-sanded and buffed to produce a high-gloss finish with similar depth to lacquer, and stood up well to weather abuse.
In the 1980s, under governmental mandates to lower the "VOCs" (volatile organic components), paints were developed to comply, introducing the "base coat/clear coat" system. These finishes feature greater durability and very high gloss, but less depth than the old lacquer finishes
Merry Christmas and Happy New Year, and keep 'em driving!