Many years ago, my mother covered a long hallway with plywood than installed mosaic tile. The tiles came in mesh-backed sheets: 4 sizes of tile, all with a rounded shape; each tile either white, black, or gray. The space between tiles varies from almost nothing to about 1/2", filled with medium-gray grout, which I don't think was sealed. In trying to get the floor into better shape, I started off by scrubbing it thoroughly with a vinegar/water mix, which got a lot of dirt off the tile and grout. On examining the floor, there are a few missing or cracked tiles, but we have extras so I can replace them. The grout has some problems: pitting and cracking here and there, a little low in places. Can this floor be regrouted and then sealed? I've read that you usually want to remove old grout before regrouting but that wouldn't be easy in this case. I figured I wouldn't have much to lose by trying to regrout the whole floor, even though the grout would be quite thin in places, then sealing. Suggestions welcome. Thx.