When building the ultimate scale rig, there’s nothing that compares to an injection-molded body. Most often referred to as “hard” bodies, the type is preferred because injection molding offers finer, crisper detailing and allows more complex shapes than the vacuum forming process used for Lexan bodies. However, painting and detailing a “hard” body requires more steps and care than spray-bombing a clear shell. The body needs to be prepped, the paint needs to go down smoothly and special care is required to get the details right. I’ve painted a lot of hard bodies in my time as an RC modeler, and I’m going to show you how to transform your truck’s body from a piece of plastic into a work of art. Follow these steps and you’ll have an award-winning paint job.
Step 1: BLACK IT OUT
The very first thing I do to all bodies is coat the inside with semi gloss black to give the body a more realistic look. When you look inside the wheel wells of a full-size truck you see nothing but black, and painting the inside of your body will give it the same look. To make this step even easier I completely skip any prep steps and simply apply the paint. You don’t need a perfect finish here but you do want to make sure you get as little overspray as possible on the outside surface of the body.
A quick coat of semi gloss black is all you need to give your truck a more realistic look. No prep work needed here; just spray away.
STEP 2: BODY PREP
If the surface below the paint isn’t perfect, your paint is going to reflect that. Prepare the body by sanding away any excess plastic with a fine-grit sanding stick. Remove any bits of sprue, mold lines, and “flash” (thin ridges of plastic formed where the plastic sneaks past the edge of the mold). Sand lightly and check your progress frequently to avoid removing too much material. If you do overdo it, use automotive spot putty to fill in the area, then sand it flush.
This Bruiser body has a pretty noticeable mold line along the left and right fenders. A little sanding will make it go away.
TIP Anytime you have to touch the body during the paint process, make sure you first wash your hands with soap and water to reduce the risk of getting oils from your fingers onto the body and possibly running your paint job.
STEP 3: PRIME IT
A base coat of primer makes it easy to see any imperfections on the surface and will make certain you get a uniform finish when you apply color. Before priming, scuff up the plastic with 800 grit wet/dry sandpaper. This knocks the shine off the plastic and gives the paint a surface to grab onto. Wash the body with soap and water and dry it thoroughly, paying special attention to any nooks and crannies that might be holding water. If you spent the time to black out the inside of the body, be sure to mask it off to keep primer overspray from getting to that black surface. I prefer Tamiya Gray Surface Primer and I warm the can before spraying to increase can pressure and allow the paint to flow better. When painting, apply enough coats to give the body uniform coverage of primer. You don’t have to worry about your spray technique here because you aren’t looking for a perfect finish; it’s all about the coverage.
As soon as you have full coverage of primer you can stop applying coats. It will give the body a uni-form finish and let you see any imperfections that you may have missed when prepping the body.
STEP 4: PREP FOR COLOR
This step is optional, but if you want a glass-like shine, it’s a must. Let the primed body sit for a few days to completely dry, then wet-sand the entire body with 1,000 grit wet/dry sandpaper. This smoothes out the surface and gives the paint a rough surface to stick to. If you happen to rub through the paint, reprime and blend the area. When you’re done sanding the body, wash it again with soap and water and make sure it’s completely dry before applying paint.
Light sanding with 1,000 grit sand-paper is all it takes to get the primer ready for paint.
STEP 5: SPRAY COLOR
Unlike the priming steps, the color coats must be laid down carefully. For the first coat, just mist the body, don’t attempt to cover it fully. You should have a thin coat of paint with signs of primer showing through. The objective is to give the next coat of paint something to hold onto. Allow about 15 minutes for the paint to “tack up,” then apply another coat. Repeat for a third coat. With each coat, apply enough paint to provide a smooth surface, and allow it to dry before handling. If you’re using Tamiya paints, you can touch the body after about two hours. If you’re using Testors/Model Master paints, wait a minimum of four hours. Ideally, you should move the body to a warm, dry, dust-free location and let it dry for about a week—the longer, the better. The harder the paint is, the better it will sand and you’ll be less likely to sand through to the primer.
STEP 6: SAND AND RECOAT
If you like the look of the body at this stage, you can skip this next step and the polishing that follows. But if you’re going for a perfect show-car finish, this is a must: when the paint is fully cured, wet-sand the body again and recoat. For Tamiya paints, repeat to apply six to eight coats. Testors/ Model Master paints spray thicker, and four coats is usually sufficient.
STEP 7: POLISH
Now, you may be happy with the finish of the body at this point and if so, you can give it a coat of wax to bring up the shine and call it a day. I like to take it a step further and polish the paint out to give it a mirror shine using sand papers from a polishing kit from Micro Mark. Polishing the paint removes the “orange peel” texture often associated with sprayed paint. If you have a lot of orange peel, start with 4,000 grit sand paper, but if you have a pretty good surface then you can skip to 6,000 and start there. Wet-sand the entire body until you have a uniform matte finish, then sand again with a finer grit sandpapers until you get to 8,000 grit. Use caution around any corners and raised areas because the paint is at its thinnest there and you can easily rub through. If you do rub through the color, spray a little paint into a mixing cup and use a fine paintbrush to blend in the area and sand if necessary. All that’s left to do after sanding is to buff the surface with wax and a soft rag to get that mirror finish you’re looking for.
If you’re adding stripes or other graphics to the body, be sure to triple-check your masking to make certain the tape is fully adhered so paint won’t bleed under, and no areas are exposed to overspray. When spraying the color, apply light coats. Don’t overdo it with thick and/or too many coats of paint, or else you will end up with a lip of paint on the edges of the graphic. Once the paint has dried you can remove the masking tape and enjoy the custom look of your truck.
STEP 8: ADD THE DETAILS
Before painting any details, wash the detail area with dish soap to remove any wax that was used to shine up the body. Wax on the surface will keep the paint from sticking properly and it will flake off later. When masking a detail part such as a door handle or window trim, I like to use Tamiya or Parma masking tape because it’s thin and easily conforms to the surface you are masking, cuts easily with a hobby knife and it gives you a nice crisp edge. Use the edge of your fingernail or back of a fine tip paintbrush to rub it down into place before trimming. Only apply paint until you have full coverage and stop to avoid building up a large unrealistic lip on the edge of the paint. With the paint applied, let it dry for about an hour then remove the masking tape.
It’s not difficult to get a high-quality finish on an injection-molded body, it just requires patience. Most goofs happen when people get impatient and handle a still-tacky body, or try to cover the body with a single coat. Don’t rush it, and if you do make a mistake, don’t sweat it too much. Unlike a Lexan body, there isn’t really any mistake you can’t undo with a hard body. Runs can be sanded out, imperfections can filled … all the techniques an auto body shop uses apply to hard plastic bodies too.
Source from: rccaraction.com