How Does Sandpaper Work?
Sandpaper works a lot like a saw, chisel, or any other cutting tool in your shop. The particles on sandpaper are made up from a number of sharp edges that cut the wood the same way a saw blade does. The only real difference is that sandpaper, unlike your saw, can’t be sharpened.
What is grit?
When talking about sandpaper "grit" is a reference to the number of abrasive particles per inch of sandpaper. The lower the grit the rougher the sandpaper and conversely, the higher the grit number the smoother the sandpaper. This make sense if you imagine how small the particles on an 800-grit sandpaper would need to be to fit into a 1" square. Sandpaper is referred to by the size of its grit (i.e. 150-grit sandpaper).
What’s grit sandpaper should I use?
Heavy sanding and stripping, roughing up the surface.
Smoothing of the surface, removing smaller imperfections and marks.
Final sanding pass before finishing the wood
Sanding between coats of stain or sealer.
Removing dust spots or marks between finish coats
Fine sanding of the finish to remove some luster or surface blemishes and scratches.