When it comes to mixing up the Rockite, "there's no real measurement to it," Chen says. He used 1.5 spray-paint caps–full of cement and added water very slowly and carefully until the mixture had the consistency of cake batter, or yogurt. "You want to keep it thick just to keep it from getting between the stone and the mold," he says. One important note: While working with the cement, keep a bucket of water nearby for washing any mixing cups or stirring sticks. After you finish, you can dump the sediment from the bucket into the garbage. "It's not harmful, you just don't want it clogging up your sink," Chen says.