Here is a bunch of info on fender guitar finishes…..the with undercoat is a common thing but some guitars got it some didnt…most of the guitars were either a desert sand undercoat or white….and in 63 they got a fullerplast sealer…for the most part…some got nothing and fender used a different clearcoat before 63 but used desert sand and white as undercoats……fullerplast is also plastic…so it is a misnomer to think that all pre cbs strats were all nitro…like i said…some may have been because they got a rush paint job and got nothing underneath…but this was not the norm.

they used sealer/fullerplast….desert sand/white undercoat…then the finish and then a clear coat over that.

When Fender switched to Alder (from Ash) as it’s primary body wood in mid 1956, many books and authorities state Femder started using a product called «Fullerplast» This is a very misunderstood product. For example, there is a picture in Tom Wheeler’s American Guitars, page 54 (upper left corner), of a man with long rubber gloves dipping bodies into a tank at Fender in the late 1950’s. The description incorrectly denotes the man is applying «Fullerplast» to the bodies. Most likely, this man is staining the Alder bodies yellow, a process used on Alder from 1956 and later before spraying the sunburst finish.
Fullerplast is a clear, sprayed chemically curing sealer, unaffected by solvents after it dries. It is made by Fuller O’Brien , hence the name «Fullerplast» (and all this time you though it was named after the city of Fullerton, the home of Fender). Fullerplast soaks into the wood and creates a seal that prevents following coats from soaking into the wood like a sponge. This means spraying the color coats is easier and the coats can be applied thinner (saving material, money and dry time). Even though alder is a «closed pore» wood, the first few coats of lacquer will soak in like a sponge without some type of sealer coat. Fullerplast dries in 15 minutes, and is paintable in one hour. It is also applied very thin.

Most experts agree the actual product «Fullerplast» (as made by Fuller O’Brien) actually started to be used around 1963 at Fender. Prior to that, Fender used other products as their sealer coat, but they did the same thing. The sealer allowed any color coat (be it sunburst or a custom color) to not soak into the wood. Since the sealer is essentially a clear inexpensive primer, less color would be needed (and color costs a lot more money than a cheap sealer).

Another misconception about Fullerplast is it’s color. The sealers Fender used including Fullerplast was clear, not yellow. The yellow seen in the unpainted portions of a 1956 and later Alder body is actually a stain or dye applied under the sealer coat. This was used to simplify the sunbursting process. The Alder bodies are dipped in a vat of yellow stain/dye. Next the Alder body is sealed with a very thin coat of clear sealer (i.e. «Fullerplast»). After drying, the sunburst procedure is continued by spraying the translucent red ( starting in 1958 ) and dark blackish-brown on the edges of the body, which completes the sunburst look. Finally a clear coat is sprayed over the entire body to seal the colors. By dipping the alder bodies in a yellow stain first, instead of spraying yellow lacquer, there is one less step of lacquer to mix, spray, and dry. *

By fall 1964, Fender changed the yellow making it more whitish and opaque to better hide flaws in the wood. This allowed Fender to use cheaper Alder with more cosmetic flaws. The more whitish yellow was then sprayed over the sealer coat, as were the red and brown of the Sunburst. That is why the red and yellow now looks much different on late 1964 and later Fenders. This new whitish-yellow bleeds through the translucent red making it more orangish. Note that even though Fender was now spraying the yellow after the Fullerplast, they still continued to stain or dye the bodies yellow before the sealer coat.

Back to the yellow stain in 1956 and later. Since it was used for Alder Sunburst bodies, sometimes you don’t see it on custom color finishes. But again, most times you do. Fender was a production shop that produced mostly Alder Sunburst finished bodies. Hence they just stained all Alder bodies with the yellow, allowing them greater production flexibility. Therefore most custom color bodies have a yellow stained body too. After all, you’re not gonna see the yellow on a custom color body, so what’s the difference? Fender just stained all Alder bodies yellow and figured out later which ones would be custom colors. Again, in most cases Fender also still used a sealer («Fullerplast») in custom color finishes too. The custom color spraying process wasn’t different from sunbursting till after the sealer step. This simplified the production process, and made Fender quick to react to market demands for Sunburst or custom colored bodies.

During 1963 and 1964, when guitar production was really high, bodies destine to be a custom color often didn’t get the yellow stain, Fullerplast, primer, and clear coat procedure. After all, if the shop was really in a hurry it can just spray the color coat right over the Alder without any preparation paint (if need be). All they did was spray more color coats (especially if a clear coat wasn’t used). This would cost more in materials (custom color paint was the most expensive paint Fender used), but it sure was quick. And often, they didn’t even clear coat the color. This was truly a «rush» paint job.

Some colors were really prone to «short cutting» by the Fender factory. For example, Sonic Blue (and to a lesser extent, Olympic White) often do not have the yellow stain. In the case of Sonic Blue, this might have happened because the yellow stain was bleeding through to the blue. Other pastel colors were also shorted cutted, having no yellow stain, no Fullerplast, and/or no clear coat.

Metallic finishes didn’t come out well using this «short cut» technique. Without a clear coat, metallic colors can oxidize due to the metal particles in the finish. And it’s difficult to apply metallic coats very heavily. Hence most metallic finished bodies went through the whole production process, and got the yellow stain, Fullerblast, undercoated, and a clear coat.
Fender was inconsistent in using undercoats on their custom color finishes. During the 1960’s, if there is an undercoat it is usually a white primer undercoat. And most often you see this white primer undercoat on metallic finishes such as Lake Placid Blue or Burgundy Mist. The pastel colors like Dakota Red, Daphne Blue, Foam Green and the like don’t often use an undercoat coat either. But then again, sometimes they do. In the Fender production shop, it all depends on where the custom color order fell in the production schedule. If Fender had the time to use undercoat, they did. If they didn’t have the time or were backordered, they didn’t bother with an undercoat (depending on the color).

So why bother with an undercoat on guitars? The reason is purely financial. In today’s prices, white nitrocellulose primer undercoat costs about $15 per gallon. Any of the Fender custom colors cost about $15 per pint, with reds costing $20 per pint. So if you use the white primer to cover the wood and make the body a consistent white color, you can use about half as much color paint for a uniform top color. This could save a considerable amount of money when painting thousands of guitars. Of course the financial disadvantage to using an undercoat is it takes more time. You have another step where you have to let the body dry. So when the production schedule allowed, Fender used an undercoat. When things were rushed, Fender didn’t.

Fender also used Sunburst (or other colors) as an undercoat to custom colors. Fender probably had an ample supply of reject Sunburst (and custom color) finished bodies that had some flaw (remember, all these guitars were painted by humans, not machines). It can be assumed that the majority of custom color finishes over other finishes are probably rejected bodies. Stripping an existing bad finish to apply another is just too much work. So shooting a new custom color over a bad finish would be killing two birds with one stone. You use up those bad Sunburst bodies without stripping, and charge 5% more for the new custom color to cover the cost of painting the same body twice (or more).

Undercoats in the 1950’s were even more inconsistent. Again, sometimes they used them and sometimes they didn’t. And the color of undercoat was inconsistent too. It ranged from off-white to Desert Sand (the DuoSonic/MusicMaster color) to even silver. Again, usually the pastel colors like Dakota Red and Black often didn’t use any undercoat. And Sunburst is also seen under some 1950’s custom colors. Probably just an easy way to use up those bad Sunburst bodies without stripping them.

Some general rules can be said about undercoats used with custom colors during the 1950s. During 1954 and some of 1955, Fender used a silver metallic undercoat beneath their custom colors. Then during 1955, that undercoat changed to a white (seemingly the same finish used on native blond Telecasters). Also Desert Sand was also sometimes used as an undercoat. It doesn’t take much to imagine why Fender used white and Desert Sand for undercoat colors – heck the spray gun was already loaded with those colors (for Telecasters and Musicmasters/Duosonics), so just use those colors as the undercoat. Less production time in changing gun colors, less cost in stocking a unique primer