Abrasive grains have a major impact on the product's grinding ability. Normally all abrasive products will have a grit size mentioned on the back. A "P" in front if the grit indicator, indicates a European FEPA standard that guarantees a uniform size of the grains within their group. Please look here for more information on
abrasives grades / gris sizes.
During production of grains, the material is crushed into small pieces. The grains will pass through a sieve to prevent that the grains of different sizes within specified tolerances (grit size) are mixed with other grit sizes. This ensures a steady removal of approximately equal size grains. This is very important because large grains can leave traces (cuts) on the surface of the sanding object that can be difficult to see before any paint / varnish is applied. The result may be that you have to repeat the sanding operation again to get rid of the cut.
Abrasive grains are divided into two main groups:
- Natural abrasive grains
- Synthetic abrasive grains
Naturally abrasive grain Natural abrasive grains are divided again into 2 groups:
Flint: "The good old" with a long tradition of hand sanding. Flint grains are soft and the grains are not very durable and not very sharp. They are found for example on the beaches of northern France and they have been used for centuries.
Garnet: A typical American product, used widely in the woodworking industry. The grains are very sharp and grinds with great aggressiveness when they are "new", but because they are not very durable the product will soon "sluggish" compared to synthetically manufacture abrasive grains.
Synthetic abrasive grains: Synthetic abrasive grains are "tougher" and more durable than the naturally-derived abrasive grains. Below is a list of three of the most commonly used.
White aluminum oxide
- Durable.
- Breaks and retain their sharpness.
- Very good for wood sanding.
- Good for machine sanding.
Brown aluminum oxide
- Extra durable.
- Less sharp - torn down without breaking.
- Applicable to both wood and metal.
- Good for machine sanding.
Silicon Carbide
- Very durable.
- Extra sharp. They break and retain their sharpness.
- Good for wood sanding.
- Good for finish sanding (car, stone, glass).
- Very good for fine sanding.
- Good for machine sanding.
