Spray Can Basics
(Those short cans like Testors Spray Enamel®, Plasti-Kote Odds n' Ends®, or Krylon Short Cuts®.)
1. Read the instructions on the can.
2. Read the warnings and hazards.
3. Think responsibly when you use any flammable spray paint.
4. If you are in doubt, use non-flammable brush-on paints for plastics available at most places plastic car model kits are sold. Test their properties on your plastic scraps.
Use at a room temperature of 70 degrees. A cold can means lower pressure inside it and a resulting coarse spray. A cold surface means slower drying and the increased chance of drips.
Avoid spraying on very humid days. (You won't find this on the can.) Spraying a liquid from high pressure to low pressure will cool it. That 70 degree paint will be about 50 degrees when it hits the surface of the model. As the solvents evaporate, there is more heat lost. On warm humid days, this will cause moisture to condense on the model while the paint is still wet. If you see some clouding of the surface, just wait and the moisture will evaporate after the paint flashes and will not cause much harm. It can cause some colors to "blush". This is a permanent milky appearance to an otherwise pure color caused by the paint's reaction to the moisture. (Lacquers are known for this problem, but you don't care because you would never use lacquer on a plastic model. It melts the plastic.) If you get a lot of condensation, you can a: wait 3 days for the coat of paint to dry and hope for less humidity to finish the job, or b: Use a hair dryer on low setting to slightly warm the model and evaporate the condensation. This may introduce some dust but will save the time of waiting. Don't use the dryer to rush the paint drying. You will only over-dry the paint surface and be fooled into recoating too soon causing sags in the paint.
Shake can for 2 minutes after the ball begins to rattle. Occasionally twirl the can to make the ball roll around the bottom. That is where the solids in the paint settled. Keep shaking. Four minutes isn't too many. Shake between coats. Some say shake 10 seconds after each minute of spraying. Especially with metallics as the metal flakes will settle quickly.
Clean surface by removing dirt, wax, grease, etc.. If you got some stern tube lubricant on your fingers, wash them before handling the plastic. Wash your hands before working on the model. Try to avoid scratching your forehead as normal skin oils will contaminate the surface. (For me, building models involves a lot of head scratching!) If you think there is oil on the plastic you are going to paint, use a dish washing liquid detergent and clean the plastic. Rinse with warm water to completely remove the detergent. Let it dry overnight before painting. Buy a "Tack Rag" from your hobby shop or in the paint department of most stores. These are rosin impregnated gauze pads that are used to remove dust from an object to be painted. Use very light, gentle pressure or the rosin may come off onto the plastic. Most contaminates in paint come from the painter's clothing. Shake out your shirt or blow it off with compressed air. (While wearing the appropriate safety goggles and hearing protection, of course.) Same with your hands and arms. Clean the surface that your model is sitting on, as well as the masking paper you used. The force of the spray can's propellant will stir up dust on any nearby surface. Reseal the tack rag into a zipper-type plastic bag and it will keep for a year or so.
(DON'T) Scuff sand rusted, glossy or hard surfaces. No need to. Hobby Enamels are compatible with the Styrene plastic that the Vac-U-Tug Jr. is made of. They will chemically bond well to the matt surface of the plastic without sanding. Hobby enamels have little "build". They don't build up thick to hide defects in the surfaces. If you sand the plastic before painting, the painted surface may retain the look of the sanding scratches. You may want to lightly sand the brass Skeg or the resin Rudder for better adhesion of the hobby enamel to those surfaces but it will do pretty well without sanding. Use fine sandpaper on the skeg & rudder.
Press nozzle firmly. Don't be a wimpy nozzle presser. As you press the nozzle down and release it up, it will spit globs of paint. That is why you must spray an area larger than the object. As your arm is moving left to right, firmly depress the nozzle BEFORE you get to the beginning of the object and don't release until AFTER you reach the end of the object. If you are painting a 24 inch by 6 inch rectangle, you will be applying an area of paint measuring at least 28 inches by 8 inches.
Spray 10 to 12 inches from the object. That is almost ONE FOOT! Use a regular piece of copy paper as an 11 inch guide. The spray nozzles in these little cans throw a round pattern. Too close and it will be heavy in the middle, causing runs. Too far away and the paint won't make it to the object. Different cans and colors give varying results. Do a brief test spray on a scrap of paper.
Spray several light coats to avoid drips. BUT NOT ONE AFTER ANOTHER. Whether you are painting a plastic model with $3.00 worth of Hobby Enamel or a Porche with $1,500.00 worth of Urethane Enamel, the application rules are the same. The first coat is a bonding coat and is never intended to provide full coverage. It should look transparent in most areas. It should be even as possible but not thick. Let it flash between coats. Flashing is a painting term that means to let the solvents in the paint evaporate. When the first coat is DRY to the touch (5-15 minutes depending on the paint & temperature) apply the second heavier coat. (Don't touch the boat. Touch a piece of masking tape or other scrap surface that has the same amount of paint as the boat you are spraying to see if has flashed.) The solvents in the second coat will be pulled into the first coat and into the air at the same time, drying (initially) in two directions at once. If you used a heavy coat as your first coat, it will run every time because it is drying only into the air. The first coat will support the second coat until it dries. Let the second coat flash. This will take 50% longer than the first coat did. "Flashed" doesn't mean dry on the surface but your finger still leaves a texture in the paint surface. "Flashed" means dry to the touch, firm and solid. Most dark colors will cover in two coats. If a third is necessary, it too should be a medium coat. Practice on a flat piece of plastic stood on end. You should be able to spray 2 coats on a vertical surface without any drips or sags. Practice with hobby enamel. Large spray cans have enamels that are faster drying and thicker texture than hobby enamels. Most people get frustrated with hobby enamels because they are so "thin and watery".
Recoat within 3 hours (1 hour for Testors® ) or after 48 hours. Hobby enamel takes 2 to 3 days to cure completely in mild temperatures. It will be dry to the touch in about 30 minutes, longer for some colors. It is possible to mask a 1-hour or 2-hour paint coating and spray another color, then spray clear over the color coats to finish the job. As long as you stay within the 3 hour window you should be fine. (Use the same brand paint for all of the colors and clear to ensure compatibility and make a small test spray to make sure it works.) After 3 hours, if you spray fresh enamel on this dry but uncured enamel, the uncured undercoat will wrinkle as it reacts to the solvents in the fresh coat. If you are in doubt, just wait a few days before the other coats. A rushed paint job will always look rushed.
Clear spray valve immediately after using by turning the can upside down and pressing the spray button until only clear gas comes out. Then, wipe the spray nozzle on a piece of towel to remove any residue on it. A spray can will last for years if properly cleared after each use. If it doesn't work later, you can swap a spray button from another can only from the same manufacturer. Be sure to wear safety glasses when doing this in case some paint is spit out in the process.