When it comes to navigating the world of coated abrasives, there are many variables to consider, and it can be complicated to identify the best solution to meet your needs. With all the options out there, and even just those available through Uneeda, it wouldn’t surprise us if you felt overwhelmed or discouraged in the search for the perfect abrasives.
In this, part one of a two-part series, we’ll cover an overview of the technical aspects of abrasives to give you a primer on what the world of abrasives has to offer.
It’s important to understand the technical aspects of the abrasives, such as:
- types of grains, how they function, and what they’re used for;
- available backings;
- formats of products;
- special coatings and fillers;
- grain coating and a basic understanding of grit.
Grains:
In general, all the grains you’ll find have been synthesized in a lab and have been designed for specific purposes. The most important things to know for our purposes is the idea of “friability” (or the nature of the grain to break and make new sharp edges).
When it comes to friability, not all grains are created equal. Some grains will become dull. In woodworking, when a grain becomes dull, that can create an uneven or blotchy finish. For woodworking, we recommend aluminum oxide for most lower-grit to medium-grit applications, and silicon carbide or aluminum oxide for some finishing or higher-grit applications.
Backings: Paper, Cloth, Film, Foam
Coated abrasives—aka sandpaper products—can be made on different sorts of substrates, of which paper is only one. Each offers various advantages and disadvantages. Here’s a brief summary:
- Paper: Generally offers one of the best finishes, but can be easily torn. Depending on the thickness of the paper, it can be more or less flexible and more or less durable. Paper is often the least expensive and is good for hand and orbital sanding and can also be used on belt sanders.
- Cloth: Cloth products are often quite durable and can be used for heavy-duty machine sanding. They come in various weights and some are sturdy, while others are flexible to match contours and profiles. Because the cloth used in these products contains a weave, this can cause an uneven scratch that could cause issues in the finish.
Cloth products are typically used in applications where durability and stock removal are the highest priorities, as well as in some cases where flexibility and durability are needed. Cloth comes in belts and discs and are typically rated for wet applications and can withstand grease; they’re also washable.
- Film: The film used for coated abrasives is generally seen to be the optimal combination of durability and flexibility for sanding discs. It provides a flat surface for the grains, while also being resistant to tearing and can bend to match profiles. These qualities mean it’s good for both leveling/shaping and finishing applications, where orbital and hand sanding will be done.
Film products (paper as well) can be combined with interface pads on orbital sanders, to aid in contour sanding, reduce swirls, and reach hard to access places.
- Foam: While coated abrasives on foam sponges can be used on white wood, they’re used more frequently for finishing applications, such as sanding between coats of finish. Two types of foam are typically used—softer, more flexible and harder, less durable. Sponges are available in two types from Uneeda: those with hook and loop backing for use on orbital sanders, and those without, made simply for hand-sanding applications.
Coatings: Open, Semi-Open, Closed
In this case, coatings refers to the percentage of space on the backing covered with grain. Open coat has the most open space, least grain coverage. This allows for a cooler sanding experience and slower or less loading. This means it’d be better to use open or semi-open in applications prone to loading, such as softer woods.
Closed coat has the most grain coverage. A closed coat will produce a more even scratch and a better finish. It’s also good for heavier stock removal, since there are physically more grains present to do the cutting.
Fillers and Chemical Coatings: Stearate, Antistatic, Various Resins
Stearate is an external coating on some coated abrasives. It acts as a lubricant to reduce friction while sanding, which reduces heat—which causes all sorts of issues, from loading to uneven finish.
Stearate is sometimes described as if you’d put soap on the sandpaper, allowing the material you’re sanding to slide out from the grains, rather than load into the sandpaper as you sand. Another benefit to reducing friction is reducing the opportunity for static to occur.
In addition to stearate, some products also include special antistatic fillers/coatings to specifically reduce static. Static electricity can be a big problem when sanding, as it can cause dust extraction to run amok. This is particularly bad in wide belt sanding, where static can cause dust to stick to the belt and within machine components, causing all sorts of other issues.
Suffice it to say that if the application you’ll be doing will be prone to generating static electricity due to friction, choosing a product with antistatic properties will be beneficial.
Formats:
Wide and Narrow Belts, Discs (PSA, Hook and Loop, with holes/without holes), Sheets, Sponges (hand sanding and for sanders), other special shapes.
Coated abrasives are available in various formats based on the machine style or whether hand sanding will be done. Choosing the format will likely be the most straightforward part of the process of identifying the right product for you, unless you’re starting from the beginning in implementing a sanding strategy.
Grits:
Coarse, Medium and Fine, and beyond
Coated abrasives come in a variety of different grits, starting as low as P8 and going to P1200 and up. Lower number grits are coarser grains and will do more stock removal, whereas higher grit numbers are finer grains and will have a much smaller cut rate.
Before making a product selection, it’s key to understand at least the basics of coated abrasives. This article just scratches the surface (no pun intended!) of these products.
Check back next week for part two of Caylena Cahill’s article from Uneeda!