I have started installing 18" travertine tile in most of my home. I have only completed only about 200 square feet so far. I have noticed that I have a slight difference in elevation from one tile to the next. I am tiling on what appears to be a flat cement floor with a 1/2 grooved troll for the thin-set. I have been told that this is normal and usually is finished with a sanding buffer to get all edges level. Is this true and is it easy enough for a handy do it yourselfer to rent a machine and do? Any suggestions or advise?