Help--shower tile covered with grout
I am so bummed--I have a cheap shower drop-in in my master bathroom, and I tried to have it jazzed up a little by having mosaic tile done all around it. The tile I picked is beautiful--sheets of rectangular tiles that are a mix of green and brown glass tile and lighter stone pieces that may be travertine. The guy who installed it did a decent job (far from perfect, but not bad). However, when he grouted, he clearly screwed up--I think he didn't wipe the grout soon enough, and ÃÂ¾ of the tile was completely coated with grout. He used the pre-mixed kind, and it was supposed to be unsanded but it was a gritty mess. He tried to tell me that this happens with "porous" stones, but he was completely full of it--this was his error. He said he would try to take care of it, and I thought he had, but when I looked more closely after he left, it was a mess still. I have scrubbed with a nylon brush and water and vinegar solution. It helped some but not too much. What seems to be working is rubbing it with a soft sandpaper block. However, my hands and wrists are killing me, and it still looks rather filmy in spots and downright coated in others.
I thought about trying to use a grout film remover, but I read the label carefully, and it said not for use with natural stone (just ceramic tile).
Any idea what I can do? I almost wonder if a power sander/buffer would work (not that I have one of those).