Shower tile hairline cracks
Hello- I recently bought a 1924 Spanish home that has had some deferred maintenance over the last decade or so. One bathroom has a 1930-1940's tiled shower stall. On the floor of this stall, there are 4 hairline cracks through the tiles. One crack extends from the center of each wall and ends at the drain in the center of the floor. They are only very thin hairline cracks- no tile has chipped out and the tiles are not damaged in any other way. The grout seems to be intact throughout the stall. Do I have to worry about water leaking through these cracks to the subfloor? Is there some way to seal these cracks without destroying the original tile? Any help is greatly appreciated.
Will that make the tiles slippery? Should I cover all of the floor tiles, or just the ones that are cracked? Thanks for your help-