Drop coating is an important skill that every auto body paint sprayer should aspire to master. Drop coats are administered during the last phase of the spraying process when metallic paints are used. When applied to an auto body panel correctly, drop coats offer full color coverage, perfect metallic content distribution and a better paint base that can accept lacquers with ease.
Applying Metallic Paint
Drop coating should be used with all metallic auto paints. Many paint sprayers apply metallic base coats using the same methods with which they apply solid colors, and this is a common error that compromises an otherwise perfect job. While horizontal arm movements are perfect for most solid color spray jobs, metallic auto body paint should be dropped onto the panel as soon as basic coverage has been achieved, and it is equally as important to cross coat the final application in horizontal and vertical directions.
Ensuring Uniform Paint Coverage
Before drop coats can be applied, the prepared car panel must be adequately covered with metallic auto body paint to help avoid primer transparency. Once the color is activated, a full wet coat of paint should be sprayed to the surface of the panel. It is essential that each horizontal spraying movement blends into the previous one to guarantee uniform coverage and distribution (overlaps of 30% to 40% are perfect). As soon as a single we coat has been applied, the auto body paint must be left to dry for around 10 minutes. Never spray a second coat until the first one has achieved a matte appearance.
Applying a Second Coat of Metallic Paint
Personally, I like to spray the next coat of paint in a different direction to the first, especially when the panel has been taken off the car. Sometimes, this isn’t possible on vertical panels, such as fenders and doors, if they are still fitted to the vehicle so don’t be too concerned if you are happier using a typical horizontal spraying pattern. The second application must be sprayed in a similar manner to the first coat, but try to achieve 80% wetness in comparison to the earlier application. Once more, the auto body paint must be left to dry for around 10 minutes until matte.
Applying the Drop Coat
If the metallic paint is still transparent, an additional coat may be required but this won’t be necessary in most cases. To spray the actual drop coat, position the spray gun 18 to 24 inches away from the surface of the panel and reduce gun pressure by 20% to 30%. Spray the auto body paint horizontally, moving the arm slowly across the panel so the metallic color drops (or falls) onto the surface. Maintain uniform coverage until the spraying process is complete. Recoat the panel from a similar distance straight away, but swap the horizontal movements for a vertical direction so the subsequent coat crosses the first. As well as guaranteeing even paint coverage, crossing the drop coat offers uniform metal distribution and a superior surface that will accept lacquer correctly.
Tacking the Drop Coat
Allow the drop coat to dry before visually inspecting the metallic auto body paint. Check for patches where coverage might be inconsistent and spray a further drop coat if necessary. With solvent-based auto body paint, it is always a good idea to run a tack rag over the vehicle panel as soon as the drop coat has dried. Specialist tack rags can be purchased for water-based auto body paint, but it is preferable to waive the tacking process as high paint build-up can peel back the color and this can lead to frustrating rework.
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