These diamond stones suck! I accidentally ordered stones from these people off ebay and not my usual supplier. The stones did ok for about 45 minutes then stopped grinding. After wasting half a day of labor for 2 men I finally called them and ask what was wrong. Apparently CHEAP diamond glaze over and stop working when they heat up per the ediamond rep I spoke with. He told me to use water to grind( a big no-no for epoxy applications) . Then he suggested I take the grinder out to the road and grind some asphalt to bring the diamond out(which is basically vandalizing a public road) then he suggest using play sand. But keep in mind I've never had this issue with my usual supplier and not really looking to spread several hundred pounds of sand over a large floor only to have to clean it up along with all the concrete dust. So he agrees to send me a replacement set of stones at no cost. I was happy to get the issue resolved. Guess what? New stones glazed over in less than an hour just like the previous ones did. Apparently all there stones are gona be cheap and glaze over. They are the cheapest stones on the internet and I see why. Save yourself a lot of time and labor cost and get decent diamonds because these cheap diamonds are not worth the savings compared to actual diamond grinding stones. I will NEVER order from these people again as I am very disappointed and dissatisfied.