Mixing Automotive Paint - Stirring The Pot
Planet Color's Paint System
While we could have refinished our project C3 in the original color, the fact is, our factory white was a little subdued for our custom Corvette cravings. If the ambition was pure stock and correct, this would have been the only choice. True, we could have strayed from original, but held within the constraints of the OEM palette; however, in this build we had already overstepped the boundaries of resto, with leanings well towards custom. So why not a custom paint? Planet Color has become quite a force in the custom paint world, with a staggering selection of color and additives, which can be used in combination for an infinite number of trick paint effects.
While going full-on is tempting, what caught our attention was a more subdued offering from Planet Color's Classic Muscle Tones line of paint. A trade show display of the available colors drew us in like a magnet when we caught sight of the number PCM26 Chumma Orange-just what we were after: hugger orange on steroids. No pearl, iridescent, flake, flip-flop, or even metallic here, just a hot, clean orange that really "pops."
So now we had the paint, but anyone can tell you that the color is just one stone in the structure. Painting is a process, starting with the foundation of the primers, building up to the color, and then finishing with the deep reflectivity of a top-quality clearcoat. When painting a car, the best and most foolproof approach is to use all the products in the process from the same manufacturer's line. The paint companies have done their homework on compatibility, ease of application and durability, so why not take advantage of their expertise? We did by using the Planet Color system from bottom to topcoat.
The world of automotive refinishing chemicals is constantly changing, due to product development and regulations in some areas. Some regions have specific VOC emissions standards that must be adhered to, and the mixing ratios of the products, or even the specific products themselves, may vary from what is shown here. Every paint supply retailer should have a product data sheet for each of the specific paint products sold. The product data sheet will detail the characteristics of the product, mix ratios, as well as application information. Be sure to get a data sheet on any product you intend to spray, and treat the information there as the last word in the compliant formulation.
Here is a detailed description of the products involved in our paint job; why they are needed; how we mixed it all up; and application notes where applicable.
Primer Surfacer
Once the heavy lifting is done with the basic bodywork, after the bondo spreaders and fiberglass are put away, it is time to pick up the spray gun for the first primer coats. For metal cars, Planet Color's step-by-step refinishing guide outlines a system of etch primer, followed by a urethane surfacer. However, for a glass-bodied car such as a Corvette, there are different requirements. We went directly to Planet Color product specialist David Kidd, who directed us to their NP75 Ultra-Fill High Solids primer. This product bites like a bulldog to fiberglass or SMC panels, and is a high-build primer with excellent sanding characteristics.
For application over bare glass and body filler, the surface preparation consists of just cleaning with a surface cleaner such as Sherwin-Williams Ultra-clean solvent. We applied three even wet coats of the NP75 surfacer, allowing the solvents to flash between coats. Following the surfacer application, our Vette was block-sanded to perfection. Our initial block sanding is a hard hit with No. 180 on a long-board, which will give the maximum leveling effect for the block sanding effort. Next, any additional minor repairs are made, as required. After the first blocking, we will go back for a second primer application; this time for flawless surface texture.
5 parts-NP75 primer
2 parts-US1-US4 reducer
1 part-NH77 catalyst
Mixing Notes
The pot life of the product once mixed is about one hour, so mix only what you will use. The US1-US4 reducers are all rated for different ambient temperatures, with US1 being the fastest evaporating, recommended for use at low temps; the US4 is the slowest recommended, for use at higher temps. We like to use somewhat slower than the recommended reducer, which helps to smooth the primer application as well as hard grainy edges. Naturally, a slower reducer increases the flash time.
DIFFICULTY INDEX ::: III ANYONE'S PROJECT | no tools required I BEGINNER | basic tools II EXPERIENCED | special tools III ACCOMPLISHED | special tools and outside help IIII PROFESSIONALS ONLY | send this work out IIIII
Primer Sealer
A sealer coat is not necessary with the NP75. This surfacer can be finish-sanded with No. 600 paper and then topcoated directly. However, for this paint job, we wanted an intermediate primer coat before the topcoat color goes on. One of the main features we wanted in the sealer coat was a tinted product that will be close to our final orange basecoat color. Here the Sherwin-Williams Spectraprime Sealer System fits our needs exactly. This sealer is available in seven primary colors, which can be intermixed to create virtually any color desired. We selected the P30R, which is red, and the P30Y, which is yellow, to produce an orange sealer.
2 parts-P30 Spectaprime
1 part-S41 converter
4 parts-SpectraSeal
2 parts-US4 reducer
1 part-H38 catalyst
Mixing Notes
SpectraSeal is made by mixing the Spectraprime P30 with the S41 Converter. Once the SpectraSeal is made, it is mixed in the ratio shown with the US4 Reducer and H38 Catalyst. The SpectraSeal is sprayed over finish-sanded primer surfacer and allowed to flash; then the basecoat application is sprayed directly over the top.
Basecoat Color
As mentioned earlier, the color we chose for our custom Corvette project is a high-impact orange hue from the Planet Color Muscle Tones line. It is exactly the high-energy tint of orange we were after for what will be a highly modified mid-'70s Vette. In a basecoat/clearcoat system, the basecoat contains all the color but none of the gloss or reflectivity of the final finish. The basecoat will appear dull once the solvents flash out of it, and the object is to lay down a smooth base with minimal texture, but obtain complete color coverage. We applied two medium coats to our Corvette, which covered beautifully over the orange-tinted sealer.
1 part-Planet Color basecoat
1 part-PCS-15/25/35/or 45 basecoat stabilizer
Mixing Notes
Here, again the solvent portion of the mix, the basecoat stabilizer is temperature dependent. Again, our preference is a little slower is better than too fast for the less surface texture and a smooth application of the basecoat. Do not use a fish-eye eliminator in the basecoat or adhesion problems with the clear may result. One-two ounces of UH100/900/904/or 924 clearcoat catalyst can be added to a quart of mixed basecoat for improved chip resistance.
Gloss Clearcoat
The clearcoat in a basecoat/clearcoat system provides all the gloss, durability, chemical resistance, and reflectivity to the final finish. A high-quality clear is an essential ingredient when the goal is show-quality paint. We selected Planet Color's parent company, Sherwin-Williams Ultra 7000 clearcoat to finish our paint project. A good clear needs to go on smooth as glass-blend the edges of the spray pattern off the gun into a seamless coating, and then buff out to a mirror finish. We applied three coats of the Ultra 7000 clear over the basecoat after allowing sufficient time for the base to flash, or about 20 minutes, given our painting conditions and solvent mix.
3 parts-CC921 clearcoat
1 part-R24/26/or 28 reducer
1 part-UH924 catalyst
Mixing Notes
Ultra 7000 Clear should be mixed just prior to the intended application, and the pot-life of the mixed product is about one to two hours, depending upon the ambient temperature. The reducer selection is temperature dependent; again our preference tends to the slower side. Up to 1/2 ounce of V3K780 fisheye eliminator can be added per sprayable quart of the clearcoat.

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