Can You Sand Single Stage Urethane Paint?by Tyler Lacoma
Many types of urethane paints require that you paint your car in stages, applying several different coats that must then be allowed to dry before the next coat is added. Depending on the sequence of steps, wet sanding is usually advised at various stages of the process, and with a process that takes four or more coats you can expect to sand twice. Single-stage urethane bypasses some of these time-consuming steps, but at a cost.
Urethane Single Stage Paints
When urethane paints are applied in stages, the last stage is applying the "clear coat" or layer of protector design to add to the sheen of the paint and protect it from damage. This is not part of the urethane process, but it is common even with single-stage urethane paints. If you choose to use a clear coat, be sure to do any necessary sanding first, since afterward you will be forced to sand through the clear coat itself. When using a single-stage paint that has a chemical hardener, you will probably need to wait only 24 hours or so before sanding. The hardener allows the paint to dry faster and more crisply, so sanding will be more effective earlier on in the process. Urethane coats that progress in stages do not generally use this type of hardener, since the layers naturally build on top of one another, but single stage brands use it to provide the necessary support to the single layer. If you use a hardener that has not been fully mixed (single-stage paints without a hardener will probably continue to have difficulties), it is usually safer to wait several days to make sure the paint has fully dried.
Sanding and Maintenance
You should only sand your urethane coat to remove problem areas, such as scratches, ridges, bubbles or other problems that have developed in the paint. Wet sanding uses a mixture of wet grit and sandpaper to sand down these flaws into a smooth surface. In multi-coat processes, 400- to 600-grit-level sandpaper can be used, followed by 1500- to 2000-rated paper in the end to remove all blemishes. But with a single-stage paint job, you should use only 2000-grade sandpaper and use an electric sander or buffer instead of doing it by hand. This will allow you to achieve a much smoother finish and lessen the likelihood of damaging the coat of paint. Single stage urethane coats, especially on metallic colors, can become dulled by the sanding process. Sometimes this dulling is expected, and you can solve it by applying protective coats of wax as soon as the paint has cured. At other times you run the risk of permanently dulling the paint, so always be careful when sanding.
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