When a project calls for sanding, one must confirm the correct materials are being used. Reason being is due to the different sizing, backing and grit of the sandpaper. But, how can we identify what type of sandpaper is best? Subjected to the work needed for your project, grit size will come into play. Thus, we must make note that sandpaper is measured by its grit size while others are measured by both the grit and grade of the backing. When buying your sandpaper, check the item to confirm it states the pressure sensitive adhesive (PSA) or the grit and size number. This will help when deciding which one is best for the project at hand.
Sandpaper Grit Sizing: If you are looking to remove a previous material such as gelcoat; begin sanding your surface with a 150 grit or lower. A low grit number determines the coarseness of the sandpaper which will give you the ability to remove materials and coatings. Sandpaper with a grit number in the 200’s and higher would be great for finishes such as buffing, polishing or the removal of small scratches. A high grit number is equivalent to how small the grains are which will allow you to smooth the surface.
Sandpaper Weight Grade: One may see grade letters ranging from A-E which represents the durability of the sandpaper, where E is the strongest. For example, (based on the figure above) the red Mirka Royal 40 grit disc would be ranked as the most durable, next the Mirka Bulldog 120 grit Gold, followed by the gray Mirka Bulldog 400 grit Gold .
Here is a great tip!
If you are looking to conduct a wet or dry sanding, the sandpaper coating must be waterproof. An abrasive that is waterproof will last you longer with end results you’re aiming for in a wet/dry process.