Mastering The Metallic Base Coat: A Guide To Perfect Spraying

Spraying a metallic base coat can be tricky, and there are a few things to keep in mind to ensure a smooth and even finish. Firstly, it is important to use the correct tip size for your spray gun; a 1.3 or 1.4 tip size is recommended for any basecoat, including metallics. You should also maintain a distance of about 12 inches from the panel when spraying to avoid striping. The paint mixture should be thinned by about 5-10% with thinners, and multiple light coats should be applied to achieve an even finish. It is crucial to follow the manufacturer's instructions, as some metallic colours require a specific application method, such as wet coats or cross coats, to achieve an even metallic finish. Additionally, the type of reducer used can impact the final result, with slower reducers being recommended to allow the paint to settle correctly.

Use a 1.3 or 1.4 tip size for any basecoat, including metallics

When spraying a metallic base coat, it is recommended to use a 1.3 or 1.4 tip size. This tip size is suitable for any basecoat, including metallics. Using a larger tip size, such as a 2.0 tip, is not advisable as this size is more suitable for primers.

To achieve the best results, it is crucial to select the appropriate spray gun nozzle tip size for your project. The tip size should be chosen based on the coating being sprayed, the project surface area, and the spray gun being used. For example, heavier coatings like primers require a larger orifice size, typically ranging from 1.7 to 2.2. On the other hand, basecoats are generally sprayed with a smaller nozzle size, such as a 1.4 to 1.6 nozzle.

When working with metallic base coats, it is essential to follow specific techniques. It is recommended to use a crisscross spraying technique, similar to a drop coat. This involves increasing the pressure slightly and maintaining a distance of about 12 inches from the panel. It is important to ensure that the metallic base coat is applied evenly. The basecoat stage provides an opportunity to experiment with the paint, allowing you to adjust the colour and ensure it lays down smoothly before sealing it with a clear coat.

Additionally, proper preparation of the surface is vital for a successful paint job. This includes cleaning and abrading the surface to create the best possible foundation for the paint application. Understanding the product and its requirements is also essential, as is matching the spray gun to the specific task at hand. While a new spray gun is not always necessary, having separate guns for different purposes, such as one dedicated to clear coats, can help prevent contamination and ensure better results.

Apply two or three coats of the prepared mixture

When applying a metallic base coat, it is important to get the technique right to avoid issues such as mottling, where the metallics settle at the bottom of the paint, or clear coat adhesion problems.

To apply two or three coats of the prepared mixture, start by thinning the paint. For single-layer metallics, thin the paint mixture by an extra 5-10% thinners only (not activator if using a 2-pack). Once the previous coat has flashed off (usually around 10 minutes, depending on the thinners), apply two to three lighter coats. Hold the gun a few inches further away from the panel than before, and leave very little flash-off time between coats. These lighter coats will give an even metallic surface while still being able to soak into the previous layers, resulting in a smooth finish.

If using cellulose paints, do not apply a finishing coat of clear cellulose or blending clear, as they do not weather well. Instead, use acrylic or two-pack lacquers. Do not apply too much thinned paint to the surface, as this can cause blotches or sagging. The surface will be slightly matte when dry, especially with cellulose paint, but it should be smooth enough to compound to a good gloss. Avoid over-use of compound or abrasive polishes, as this can cause a "greyed" effect on the aluminium flakes in the paint.

For basecoat metallic colours, follow the manufacturer's instructions. Some require a "wet" coat, while others may need one or two cross coats (lighter coats) to achieve an even, cloud-free finish. Ensure the basecoat is allowed to flash off, but not dry, before applying the lacquer. Any stripes, dirt, or other defects will be locked in once the lacquer is applied. To minimise dust problems between coats and before lacquering, use special basecoat "tack-rags", ensuring the surface is touch-dry first.

Thin the paint mixture by 5-10% more than before

When applying a metallic base coat, it's important to get the paint consistency right. This is achieved by thinning the paint with a reducer or thinner. For single-layer metallics, the paint mixture should be thinned by about 5-10% more than before. This extra thinning ensures that the paint can be applied in lighter coats, creating an even metallic surface while still being able to soak into the previous layers, resulting in a smooth finish.

To thin the paint mixture, you can use a reducer or thinner, which helps to avoid solid clumps or "orange peel" textures in your coat. The amount of thinner or reducer to add depends on the paint's technical information, which can usually be found on the side of the can. It's important to follow the manufacturer's instructions and use the recommended thinning ratio.

Once you've thinned the paint, it's crucial to test the mixture before applying it to the surface. This can be done by adding a small amount of paint to a spray gun and spraying it onto a disposable surface, such as a wooden board or an old piece of equipment. If the paint is not flowing well from the spray gun, you may need to add a little more thinner to improve the flow.

After thinning and testing the paint, you can proceed with applying the metallic base coat. Hold the spray gun about a foot away from the surface and sweep it side to side or up and down to coat the object evenly. Remember to shake the can regularly during the process to maintain a consistent paint mixture.

By following these instructions and thinning the paint mixture by 5-10% more than before, you can achieve a smooth and even metallic base coat finish.

Use a slower reducer to control mottling

When spraying a metallic base coat, using a slower reducer helps control mottling, which is essential for achieving a professional-looking finish. Mottling refers to the uneven appearance of the paint, with darker and lighter patches creating a blotchy effect. By using a slower reducer, you can slow down the drying time of the paint, allowing the solvents to escape and preventing them from getting trapped under the top layer. This is crucial because trapped solvents can lead to issues such as pinholes, shrinkage, and loss of gloss.

The key to controlling mottling is to ensure that the paint has sufficient flash-off time between coats. Flash-off time refers to the period when the solvents in the paint evaporate, allowing the paint to dry and cure. If the paint dries too quickly due to a fast reducer, it can trap solvents underneath, resulting in an uneven finish. By using a slower reducer, you can extend the flash-off time, giving the solvents more opportunity to escape.

It's important to match the reducer to the temperature conditions you're spraying in. A slower reducer is ideal for higher temperatures, as it prevents the paint from flashing off too quickly. In contrast, a fast reducer is designed for colder temperatures, as it speeds up the drying process. However, if used in warmer conditions, a fast reducer can cause the paint to dry too fast, leading to potential issues.

Additionally, it's worth noting that the SPI website recommends using the slowest possible reducer for the best results. This advice applies to most manufacturers, as a slower reducer allows for better solvent release. When in doubt, it's always a good idea to refer to the manufacturer's instructions and technical sheets for specific recommendations on reducer selection.

By following these guidelines and using a slower reducer, you can effectively control mottling and achieve a smooth and even finish when spraying a metallic base coat.

Use a mist or drop coat to even out the metallic finish

When spraying a metallic base coat, you may encounter issues such as mottling or streaks. A mist or drop coat can help to rectify these issues and even out the metallic finish.

A mist or drop coat is applied in the same way as a regular coat, but at a greater distance from the surface. This technique is used to smooth out the metallics and even out the finish. The distance from the surface should be increased from 6" to 10-12". You should also use a slower pass with a full trigger pull. It is important to note that increasing the pressure or using a higher volume of paint can cause de-lamination and adhesion issues.

There are differing opinions on whether to increase or decrease the pressure when applying a mist or drop coat. Some painters suggest increasing the pressure, while others recommend decreasing it. Similarly, some suggest increasing the flow volume, while others advise decreasing it. The key is to apply the coat before the previous coat dries, as this will help the coats adhere to each other.

When applying a mist or drop coat, hold the gun about 2 feet away from the panel and spray the paint in semi-fast strokes. This will create a hazy, even finish. It may take multiple coats to achieve the desired result. Once you are happy with the finish, you can move on to the next step, which is usually a clear coat.

It is important to note that a mist or drop coat is not always necessary when spraying a metallic base coat. With practice and the right techniques, you can achieve a smooth and even finish without needing to resort to a mist or drop coat. However, if you do encounter issues with mottling or streaks, a mist or drop coat can be a useful tool to correct them.

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