PS33 Disc

Klingspor Abrasives PS33 (Known As Stearated Discs) is a non-loading, semi-open coat, aluminum oxide (AO), resin over resin coated, paper-backed abrasive. This means you get exceptional service life, a clean sanded surface in bare wood sanding applications. Can also be used on primers, solid surface, aluminum and paints.

Stearate coating

The image above shows what a Stearate coating on top of an abrasive would look like. Notice the cascade look of the stearate.

Our PS33 Stearate discs, grits 40-320, are NOT top coated with a stearate. Instead, the Stearate is mixed into the resin that holds the AO grain onto the disc. This means the disc will not shed stearate onto the work surface, which has been known to create finishing issues with water-based finishes. Semi-Open Coat refers to the amount of grain covering the surface of the disc. See Abrasive Coatings for more details.

Resin Over Resin (ROR) coating is how the abrasive grain is applied and locked onto the backer substrate.
With the PS33 Stearated discs, you have a phenolic resin maker coat applied to the paper backer, which then the AO is electrostatically aligned perpendicularly, for maximum grain exposure and a size coat of phenolic resin is applied over top to lock in the AO grain.

Coated Abrasives

With the picture above, you'll see that the grain does not fall onto the maker coated backer, but rather pulled from below into the resin. This locks the grain deeper into the resin coat making abrasive grain shedding less likely to occur.

Open vs Closed Coat
Sanding bare-wood, you should always use an open (50%) to Semi-Open Coat (75%) abrasive. The disc on the left is a Semi-Open Coat while the disc on the right is a closed coat (100%) You'll notice that these discs, used for the same amount of time on the same wood (American Black Walnut) have different loadings across the disc.

PS33 Stearated Aluminum Oxide

Klingspor's Woodworking Shop recommended bare wood sanding disc is the PS33. Due to it's non-loading, exceptional service life, smooth sanded surface and the wide grit range of 40-1500 it's the go-to workhorse in our abrasive line-up.
You can find Stearated Aluminum Oxide in Sheets, Discs, and Rolls of all sizes.
(Grits 400-1500 are Stearate coated for Solid Surface and paint applications.)
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