Hi, we have recently had mitred edges done on our bathroom niche as well as the corner of our built in bath. My builder is insisting on corking these corners to prevent any water damage however i feel corking defeats the purpose of a nice mitred edge and in all online pictures these edges look grouted ? Am I wrong in thinking it should be grouted instead. I have no professional background so can only argue on what I have seen online which obviously doesn't make for a very good case? Please someone help!!!