How can I tell if water has damaged bathroom floor?

[Penelope Vandergast]

Next to the shower/bathtub, my bathroom floor tiles have lost most of their grout, exactly in the place where water tends to splash out when someone is in the shower. The floor has been like this for years. (I know, I know....) I always mop it up quickly, but it's very possible that water has seeped into the places where the grout is missing. Not steadily, like with a leak, but intermittently whenever someone showers -- every few days.

I want to fix this now. How can I tell if the floor has been water damaged? I would just replace the grout but I don't want to seal in a damp subfloor. The house is 100 years old, renovated about 15 years ago before I bought it.

[Greg]

It's likely damaged.  One way to try to find out is to remove a tile or two to inspect the tile backer, if there is some present.  A probe style moisture meter can be used to probe for moisture in and/or below the backer.  If the tile comes up easily, it's saturated.

Another way to test for moisture is to tape a 12" square of clear plastic to the floor, sealing the edges.  If condensation forms under the plastic after 24 hours, it's wet.

[phred]

if house is a hundred years old the tiles were probably set in mud rather than using backer board.
  Is the floor extra bouncy?  Has it buckled any?  Run the hair dryer/heat gun for several minutes to make sure is dry.  Tape over a piece of clear plastic - as already mnetioned - to see if any moisture remains.  Repeat with heat gun if necess.  Regrout.  Tiles stores sell little grout saws to remove old grout

[Adam Zapple]

I agree with the other posters here.  I just wanted to add that the tile store will carry a silicone based flexible grout that comes in a tube.  They have various colors.  It probably won't be an exact match to what you have but it may hold you over for a while until you do a permanent repair.