Color sanding is an important step to giving your clear-coated carbon fiber parts outstanding depth and brilliant shine. Also called wet sanding, it is simply the application of water and high-grit sandpaper after the clear coating process.
Often, to save time, pneumatic or electric tools are used in this sanding process, especially on large flat areas. However, this process has its pitfalls, so we would like to identify some issues and offer advice that we've found helps avoid them entirely.
Swirl marks, or pig-tails, are a result of using dual action random orbital sanders (DA) or similar rotary tools, while finish sanding. Even with high grit papers up to 4,000 grit, you can be left with pig-tail like swirls in your clear coat. We recommend these methods for avoiding and removing those swirl marks:
A lot of these swirls are the result of outside contaminants on your pad. Keep your work area and parts clear of dust and debris by rinsing off your paper or pad and the part frequently. Anytime you lift sandpaper off the part is an invitation for debris to make its way in, and leave scratches behind once you start sanding again. A good rule of thumb is to rinse everything off anytime you break contact between the paper and the surface. this includes the part, the pad, and the sandpaper. Working in a sink with faucet is ideal.
Always follow up sanding tools with good old fashioned hand blocking.
Nothing sands like fresh paper. We keep a bucket of fresh 1200 and 1500 Mirka sheets in water with a splash of dish soap while we are color sanding, which we swap in frequently.
Use long strokes when hand blocking to spread out how often and how concentrated your sanding pattern changes direction. This tip is especially important for spot treating surface defects. If you choose otherwise, you might end up with areas of dense haze, which means extra time buffing or sanding, and any extra sanding means you come closer to burning through your clear coat.
Avoid using heavy pressure while sanding. With higher grits, you don't need to apply much weight at all to remove texture. In fact, if you apply downward pressure to your strokes, you run the risk of creating deeper scratches than what you were trying to remove in the first place. The best advice here is to remember that the weight of the tool in your hand is all the weight you'll need.
If you do leave behind deep sanding marks, you can always drop down your sandpaper grit to remove them quickly then climb back up to 1500. In this situation it is best to keep your sanding to a concentrated area, then feather out that area with higher grit papers, with the goal of blending the corrected area with the surrounding surface.
We hope these tips will be useful in your own projects, and that they help you avoid unnecessary time spent correcting your finish.