A Complete Guide to Sandpaper Grit Classification
A sandpaper's grit refers to the size of the abrasive materials on the paper. There are various standards that exist for ascertaining sandpaper grit size, but common standards include the Coated Abrasive Manufacturers Institute (CAMI) and the Federation of European Producers of Abrasives (FEPA). Regardless of which standard you use to measure, a general rule is that the lower the number of the sandpaper grit, the coarser the grit grade will be.
TIP: No matter what type of sandpaper you're working with, you should always be sure that the bond between sandpaper grit and backing material is not separated during usage.
Macro grit sandpapers range across the following sub-types. The one thing they all have in common is that abrasive papers in this family all have fewer grains, but the grains they have are large.
This highly coarse sandpaper grit ensures expedited removal of all kinds of material. Because of the roughness, extra coarse sandpaper is used for the initial round of sanding on hardwood flooring. As per the FEPA standards, the sandpaper grit sizing is denoted by P30, P36, P12, and P16, while the CAMI standards denote the classes as 24, 30, or 36. The average diameter of the sandpaper grit particles can range anywhere between 530 to 1815 micrometers.
These types of sandpaper grit classes ensure rapid material removal. As per FEPA standards, these are classified as P40 or P50 and are denoted as 40, 50, or 60 by CAMI standards. The typical diameter of the sandpaper grit ranges between 336 to 425 micrometers. This sandpaper allows you to clear away a layer of finish or debris with little effort. However, it may not leave behind the smoothest surface texture.
This kind of grit is used to sand bare wood to prepare it for varnish removal or final finishing. The FEPA standards denote such types of sandpaper grit by P60, or P80, and CAMI standards denote it as 80. The diameter of the particles ranges between 190 to 265 micrometers.
These kinds of sandpaper grit are used to prepare wood for the finishing. Such sandpaper grit types are not suited for varnish removal or removing paint on wood. These can also be used to clean plaster as well as water stains present on wood. The FEPA standards denote such sandpaper grit types as P100 or P120 while CAMI standards denote them as 100 and 120. The diameter size of the particles ranges between 115 and 162 micrometers.
Very fine sandpaper grit is used for sanding over bare wood. As per FEPA standards, such sandpaper grit is denoted by P150, P180, and P220, while CAMI standards denote them as 150, 180, or 220. The diameter of the particles ranges between 66 to 100 micrometers.
The micro grit types of sandpaper grit are classified as follows and are primarily used for small, precise sanding, like taking off coats of finish or smoothing small areas of buildup.
Despite the identical name to the abrasive paper category listed above, very fine micro grits are distinct and are used for sanding finishes in between consecutive coats on either wood or drywall. FEPA classifications are P240, P280, P320, or P360 while CAMI classifications are denoted as 240. The diameter size is between 40.5 to 58.5 micrometers.
This is used to initiate wood polishing. FEPA standards classify these types of sandpaper grit as P400, P500, or P600 while CAMI classifies them as 360 or 320, and diameter sizes range between 25.8 to 36.0 micrometers.
Super fine micro grade paper is ideal to sand the final layer of finish on wood. It is just strong enough to thin patches and small inconsistencies in the layer's application, but not rough enough to actually remove anything that would want to be kept. FEPA classifies them as P800, P1000, or P1200 while CAMI classifies them as 400, 500, or 600, and average diameter sizes range from 15.3 to 23.0 micrometers.
This is one of the most delicate abrasives and is appropriately used for polishing thick finishes and performing final sanding. FEPA classifies them as P1500, P2000, or P2500, while CAMI classifies these as 800 or 1000, and the average diameter size of particles ranges between 8.4 to 12.6 micrometers.