Concrete countertops are usually ground and polished wet using a diamond grinder. This article explains how to use a wet grinder/polisher most effectively.
Keep it even:
Do not use a wet grinder like a high-speed metal grinder. With wet grinders, the whole face of the grinding disc or turbo-cup wheel should be pressed evenly against the concrete. This way the disc wears evenly and the concrete is not gouged. Grinding with just the outer edge of the disc touching the concrete will wear out the rim of the disc and create crescent shaped gouges in the concrete.
Don’t use too much pressure:
Grinding with diamonds does not require great pressure. Just enough pressure is needed to hold the grinding disc flat against the concrete. The faster the disc spins, the faster it grinds.
Use the right amount of water:
Diamonds require plenty of water to cool the disc and to flush cuttings away. (This is especially critical when honing with resin-bond discs, since the resin will wear away very quickly if the discs are run without enough water.) Water flow from the grinder is adjusted so that a moderate amount of water is supplied to the center of the grinding disc. Too much water makes a mess, while too little causes excessive tooling wear.
The ideal amount is to adjust the water during grinding so that the water flowing out from under the spinning disc is just clear. Less water will look muddy with cuttings, and too much water will waste water and make a big mess fast.
Always start grinding with more water than is needed, and decrease the flow to the ideal amount. NEVER run diamond tooling dry (unless it is specifically made to do so), especially the resin-bond discs.
For more information about the entire process as well as diamond pads, please see this video: