I recently had Corian counters installed in my kitchen. The contractor said it would be finished with 250 grit. The counters seem dull and when viewed at an angle, they show faint sanding lines. Water does not wipe up easily but remains on the counter as a thin film or small pools that dry and leave hard water marks. Is a 250 grit finish the standard for Corian? Should I call my contractor and ask him to refinish?