Hi. I am working on the final stage of my first carbon fiber skinning project. I used all XRC products and carbon from easy composites and the process went smoothly. I did do some of the early sanding with a random orbital sander at 240 grit. I then wet sanded by hand using circular motions from 400 up to 3000. At that stage, the product looked really good, but had a dull, matte finish. I don't recall having any noticeable swirl marks at that time, but it is possible they just weren't visible.

Anyways, today I did the polishing. I did all polishing using pads that I also bought on easy composite and attached to my random orbital sander. I started with the NW1 super cutting compound ( black ), then used the TopFinish 2 ( black ), and then finished it off with the EasyGloss.

Below is the final result. As you can see, there are a lot of swirl marks. I'm not really sure how to proceed now. Should I just try a second round of polishing? Should I go all the way back to the sanding stage? Should I give it another coat of resin? Or should I spray it with some automotive clear coat? I have the clear coat and wouldn't mind doing that, but would that fill in the swirl marks? I don't want to spray it and then regret it.

What do you guys with experience recommend?

Thanks!

Print-through is an effect you get in composites as a result of the shrinkage of the resin. All resins shrink as they cure, and for the most part that occurs in the mould while the surface is supported. But after demoulding the resin continues to shrink a little more, and now the surface is unsupported - so the surface loses its flatness fibres start to become visible in the resin, 'printing' onto the surface. If the part is exposed to higher temperatures than it was cured at, such as sitting in the sun, then the resin will soften and it will print.

The effect is worse in low resin content processes like infusion and pre-preg, because there is less resin for the fibres to 'float' in. It is especially bad when you have cores or other things in the layup that cause a small degree of bridging where the resin pools and shrinks more, and you end up with the shape of the core or whatever is embedded in the layup printing onto the surface as well.