Understanding sandpaper

Sanding products come in many shapes and forms – each with its own intended purpose. Make sure you know what you are selling.

UNDERSTANDING SANDPAPER

If you dissect a piece of sandpaper, you will find it is made up of three layers.

THE BACKING

Layer number one is the backing material. The backing for sandpaper can be made from a variety of materials, with paper being the most common. Other materials include polyester, cotton and rayon, which are more durable than paper. These cloth-like backings are used for sanding belts and discs.

Backings are classified in different weight categories. For paper backing, the weight categories range from A to F, with A being the lightest and F the heaviest. The weight of cloth-based backings is indicated by the letters J, X, Y, T and M, with J being the lightest and M being the heaviest.

ABRASIVE MATERIAL

Layer number two is the adhesive that binds the abrasive material to the backing. This adhesive should be durable; otherwise the sandpaper won’t last very long. Nowadays, the first choice in adhesive is resin. There are a few others, but the two used most often are urea resin for handheld sandpaper and phenolic resin for power sanding. The reason phenolic resin is used in power sanding is because it holds up much better against the heat that is generated. It is strong and water resistant. Two coats of adhesive are applied – the first is applied to the backing and the second is applied after the abrasive material is attached, and covers the entire surface.

THE GRIT

The third layer is the grit, which is the material that does the actual sanding. It can be natural, such as garnet, or man-made, such as aluminium oxide or silicon carbide. Some sandpapers are better suited for sanding certain materials. The two grits used most often by woodworkers are aluminium oxide and garnet, while silicon carbide and ceramic are best suited for sanding metals.

The abrasive aggregate is selected according to the hardness of the material being cut.

• Aluminium oxide

• Silicone oxide

• Zirconia.

Aluminium oxide (light brown in colour) has a high degree of friability. What this means is that the sandpaper renews itself when heat and pressure are applied. The aluminium oxide fragments and creates new sharp edges. This property allows the sandpaper to last longer than other types of sandpaper. It is especially good for stripping old varnish and paint when sanding hardwoods.

THE TYPES OF SANDING PRODUCTS INCLUDE:

• Coated abrasive rolls

• Coated abrasive sheets

• Coated abrasive discs

• Coated abrasives for hand held grinding machines with or without holes for dust extraction

• Vulcanised fibre discs

• Narrow and wide abrasive belts

• Cylindrical sleeves with holding fixtures

• Flap wheel with flange

• Flap wheels with shafts.