While no sandpaper will last forever, the type of coating of the sandpaper has will help to increase the life of the product and achieve a better finish.

The coating refers to the overall coverage of abrasive grain particles (such as aluminum oxide or silicon carbide) which are affixed to the backing material of the product, or rather, how much space is filled or not filled with abrasive grains. There are generally three types of coating options available: open, semi-open and closed – each with a different ratio of grain and each with a different optimal application. 

Closed coat
A closed coat offers the most grain coverage, coming in at around 90-95 percent coverage on the product. This type of coating is best for sanding in a raw wood state, i.e., sanding with coarser grains. This works well because the rough sanding produces larger pieces, and with harder woods, there is also less pitch (wood resin), so the heat has less of an impact. There is less need for space between grains because they will not load as much in the first place. Additionally, with coarser grains, there is naturally more space between the tips of the grain, simply because the larger grains take up more space and fewer of them can fit on any particular size of surface area.

Closed coat products are also used for sealers, lacquers and in other finishing applications to obtain the most uniform scratch pattern and highest quality finish. If you’re grinding hard metals, you’ll want to stick with closed coats as well, to maximize the amount of grain cutting the hard material.
The benefit here is that the closed coats have more grains, and the harder woods have less pitch, so the paper will not load as quickly anyway.

Semi-open coat
A semi-open coat offers 70-75 percent coverage of grains, a nice happy medium. This level of coating is useful for hardwoods, such as oak, cherry and maple, in the raw wood stage.
Similar to the closed coat, with harder woods, there is less resin present in the wood, so less opportunity for sticky residue.

Open coat
With the most open space of the three coatings, coming in around 60-65% coverage of grains, this type is best for softer materials, including softwoods like pine and poplar, as well as softer metals, both for coarse sanding and polishing. With the extra space between the grains, there is more likelihood for the waste material to simply fall off, thereby taking a longer time to load the paper.

Conclusion
To maximize the life of the abrasives making sure to choose the appropriate product based on the application is essential. Quickly clogged sandpaper is one of the most common and frustrating problems known to anyone who sands. While it’s difficult to avoid completely, particularly when sanding softwoods and lower melting point metals, choosing an open coat product for these applications can help minimize the effects of loading, due to the additional space between grains. When sanding harder materials, or rough sanding, closed or semi-open coats can be used.

Ultimately, choosing the right abrasive material for the woodworking application will help you get the best finish in the most efficient way.

Source: Uneeda Enterprizes. For more information call 845-582-3849 or visit Sandpaper.com.