Flooring Tile - how to repair a flagstone floor

We do have flagstones in our hallway, they are sealed with some translucent, brownish, leathery stuff. This is peeling and bubbles appear, the concrete in the grouts has become like sand in some places. I would ike to know what that stuff is. Kathrin

Kathrin, I'm not sure how long the stone has been down but the brown leathery, translucent stuff sounds like the patina of your stone floor. Patina is (can be) a nice way of saying it may be a little dirty and in need of a maintainence overhaul, KIDDING!. Your floor should have developed a patina by now but should not include what you described. It sounds like it may be a build up of finish and dirt or other contaminants You should consider the use of a heavy duty stripper and get the stone down to, as close as you can, its original state. Then use a water based sealer and finish to get it to the desired luster (water based because I assume you are living in the home). As for the sandy concrete between the stone, it is just that. It is probably a masons mortar or brick mortar as opposed to grout. I would assume it to be a gray color (or perhaps a leathery brown color). If you are going to patch the missing mortar area, and after the floor is stripped the mortar is still a little brownish in color, mix up a little mortar for the repai and throw a small amount of dry dirt into the mix until acheive an approximate color match (if you need more than a small handfull in a large coffee can than go to a cement colorant to acheive the color match rather than destroy the integrity of the mortar since it is already inferior to grout as far as the floor is concerned). Hope this helps and if I have missed the mark write back and we can try again. Good luck!