If you pick up any stone supply catalog, you will find endless types of abrasives used to face polish stone. Which one is best and which one do you use for which application? The following is a guide that may help to end the confusion.
There are many types of abrasives in the world, even within sandpaper. Abrasives come in all shapes and sizes. You can buy discs, belts, cup wheels, bricks, plates, bits, powders, hand pads, etc. For face polishing stone we will limit our discussion to silicon carbide and diamond abrasives in the form of hand pads, discs, plates, bricks (Frankfurt segments) and powders.
Silicon carbide describes the material that actually does the grinding, honing or polishing. Because silica and carborundum are harder than slate, limestone, onyx, marble and granite this abrasive can be used on these materials. I do not recommend grinding without the use of proper personal protective equipment (PPE), especially if grinding granite dry with a silicon carbide abrasive. Silicone carbide abrasives do not cut as fast or wear as long as diamond abrasives, which can be both an advantage as well as a disadvantage at times.
Most shops had experiences with silicon carbide before the widespread introduction of diamond abrasives. I do use all new abrasives, tools and equipment myself to become familiar with its features, advantages and limitations.
Silicon carbide is about a 9.5 on the Mohs' hardness scale, and most silicon carbide abrasives are known as loose abrasives. Silicon carbide is very short lived, as any stone craftsman can tell you. They work by sloughly off the paper or wheel. Take a silicon carbide disc and rub it on a piece of stone. Now, rub your hand across the surface and feel the abrasive that is left behind.
Diamonds are much harder than marble, granite and silicon carbide; which means that they cut (grind, hone and polish) much faster. Because diamond abrasives cost more, many people debate the issue of whether they are actually worth the additional cost. In my experience, I would say yes to most applications. The cost of diamond abrasives has decreased over the last few years because of better technology and competition. When diamonds were first introduced, many people would argue that they would get ripples (an indented surface, not flat) in a polish, but now with more rigid bonds and backer pads, as well as better techniques, this problem can be eliminated.
The diamond abrasives may require dressing, or opening up, on occasion. Because of the cost, you do not want to discard them when they stop cutting aggressively unless they are worn-out. I normally recommend using an inexpensive silicon carbide brick or stone. You can also use a soft brick, cinder block or another diamond abrasive. Diamond dressing tools are made and available if you look hard enough. Diamond blades can be dressed in the same manner. Ask the manufacturer or manufacturer's representative how they recommend dressing the abrasive.
Diamonds are a 10 on the Moh's hardness scale and, unlike silicon carbide and other loose abrasives, are known as fixed abrasives. In other words the diamond wears and does not come off the backer. Take a diamond disc and rub it on the stone and then rub your hand across the surface as you did in the experiment above. You won't feel the grit because the diamond is fixed.
Today's diamonds are available in many bonding types. The bond is how the diamond is attached to the pad. There are metal and resin bonds, electroplated, extruded, and the list goes on and on. It is beyond the scope of this article to discuss the manufacturing differences, but for our discussion we will break it down to metal vs. resin bond.