The Silicone Carbide variety of sandpapers have been the staple of finishing for guitar makers for quite some time now (this includes me as well). Typically this variety of paper is termed ‘wet-dry’ sandpaper too. It is usually made for use on hard finishes or for metal sanding, but it does work very nicely for wet sanding a guitar finish.
Some builders use it to sand wood as well, although I have never used it for that purpose, but understand it works quite well. Most often the type that is used on wood is the white or bluish-gray variety, which utilize sterates to shed the sawdust, and thus qualify as a ‘no-load’ type sandpaper.
Be aware that the stearates that are used in the no-load papers can easily, and most likely cause fish-eyes in water-borne finishes.
Loading Type of Silicone Carbide Sandpapers:
The loading type of Silicone Carbide sandpaper can be recognized by it’s black or greenish black hue. This is the type of paper that I am most familiar with and have used extensively for sanding a guitar finish in preparation for buffing the finish with a wheel.
The loading type of Silicone Carbide papers are available in the CAMI scale, JS-scale, and P-scale. Remember that the traditional CAMI-scale papers can have a stray grit particle that can cause scratching, so it is better if you can get your hands on some P or JS paper. One very good P-scale paper is 3M’s Imperial Silicone Carbide Wet-Dry Sandpaper.
Again, to keep this paper from loading you will need to wet-sand with it. I will have an entire section on wet sanding a finish, but the short story is put just a couple drops of dish-washing soap into a small dish of warm water. This will keep the sandpaper from loading or scratching, and it will keep it well-lubricated. You do need to wash the finish thoroughly before applying your finish or you risk bonding issues of subsequent coats of lacquer.
When you wet sand with the 3M Imperial, be sure to go at it carefully and not too aggresive as it cuts very quickly (much quicker than it seams), and you can easily go through you finish and sand down to bare wood. Unfortunately, this has happened to me more than a few times in my guitar building career. That is an awful feeling and means you have to apply many more coats of finish.
Grit for grit, the silicone carbide cuts much more quickly than does the aluminum oxide paper and you can get some scratching with finer papers if you aren’t careful. Probably a P1000 or p1200 would equal a P800 aluminum oxide paper.