I have a toilet that has a small leak around the wax ring for many years before it was discovered. The floor around the toilet flange is hardwood (oak) on plywood subfloor. The leak did not cause the floor to buckle or water to drip into the crawlspace. The leak was just absorbed into the flooring/subfloor. The only indication of something wrong was a musty odor that I couldn't figure out until recently.

I checked the other side of the subfloor in the crawlspace and saw a small black stain surrounding the drainage pipe. Surprisingly the stain is no bigger than a donut. I expect years of water damage would cause more damage. Perhaps there is unseen damage and that's what's worrying me.

If water is trapped between the hardwood floor and the subfloor, can they travel more than a few inches away from the flange?

I'm sure there is some mold growing in there, but I don't know if there's enough mold to justify ripping out the entire bathroom floor. I do still smell slight musty odor in the bathroom ocassionally.

I could rip out the bathroom floor to look, but would it be better to cut out a small square of subfloor from below, say, 1 foot away from the flange and fix the hole if there's no mold or water damage?

 

The big issue will be the area around the toilet flange. Our way of using wax rings requires that there be absolutely no movement between the toilet flange and toilet. The floor further out that supports your toilet might still be solid. The next is to see if the wood that's holding the toilet flange is still solid or not.

 

Once you remove the commode you should be able to judge the condition of the subfloor. Poke it with a knife or screwdriver if you need to.

 

Since I'm able to put the commode back and it is not rocking, doesn't that imply the subfloor is still good?

 

Good where? The only way to tell is to inspect the floor when the toilet is removed.

 

I had a leaking seal once and the subfloor was damaged from water and mold. I pulled the flooring, scabbed a new piece of subfloor in where is was supported by the studs, put down some leveling compound, and put new flooring in. Bathrooms aren't that big, and that's why I like to put sheet flooring in, cause it goes over the entire floor and any water won't go anywhere if done right.

 

Sheet flooring is no guarantee that a leaking wax seal won't damage the subfloor. I've seen more than a few where the leak got under the vinyl where it stops under the commode. I do agree that vinyl or tile is a better choice for a bath with a tub/shower.