What is GRIT?
The grit or grade of sandpaper is based on the number of sand granules per square inch of paper. The higher the number, the finer the grade. Lower-numbered grades denote coarser sandpaper.
Extreme caution should be used when using extra coarse sandpaper. Most commonly used on exterior surfaces for heavy paint removal. Extra Coarse sandpaper can also be used to shape wood. Power sanders tend to use these grit numbers the most effectively. Always follow up an extra coarse sanding project with finer sandpaper to remove any scratches left by the aggressive grit.
Similar to the Extra Coarse sandpaper but can be more forgiving. It can be used to remove previous finishes and for rough shaping of wood. It will also need to be sanded with a finer paper to remove any scratches left from the aggressive grit.
Used for primary sanding of rough wood and the removal of planning marks on wood. Most versatile option. It can prepare a bare surface for a finish, smooth out a work piece, or remove scratches pretty effectively. Usually recommended to sand over a medium sandpaper with fine or very fine sandpaper when a smooth finish is desired.
Used for finishing work. It can remove raised fibers or create scuffing between coats to finalize a smooth finish. For most home workshops, this sandpaper will suffice for final sanding before the job is complete.
Used between coats of paint or varnish. Superfine sheets with grits 600 and higher are best-suited for polishing jobs. These grits will leave the ultimate finish.
Always sand in the direction of the grain--never perpendicular to it or at an angle.
Scratches made by sanding against the grain will look unattractive on the finished piece and will be particularly noticeable after staining.
Wood dust from sanding will cause problems if it's not removed from the surface before staining. Dry rags or brushes aren't the most effective tools for removing dust. Instead, use a tack cloth, a sticky piece of cheesecloth made especially for this purpose.
Always wear a respirator and safety goggles/glasses when sanding.