Blue, my in-laws had a similar problem, except their upstairs hall bathroom was above their dining room. Whenever children & grandchildren splashed water out of the tub/shower, it found its way to the dining room ceiling. Their home (built in the early-60s & considered to be "an executive's" residence, FWIW), had no water proofing membrance beneath the tile floor. No one ever considered sealing the grout, either. The tile was installed over a wood subfloor, not concrete board. My dh & BILs discovered the subfloor issue when they finally demo'd the floor. We also discovered a similar problem in a former home. In both houses, corrective measures were taken but we still exercised great caution about keeping water from splashing out.

Perhaps one of the pros here will weigh in with a better suggestion, but my guess is that you'll need to tear out the existing floor and start from scratch. Sorry.

When you say it's coming through the floor - where? Through tile grout? At the juncture of the wall/floor?

Gina W, I'm not completely sure which one. Last year I tried to fix what I thought was the leak: fixed dripping angle stop and caulked heavily at base of tub. The leak came back. Caulking at corner of tub/wall/floor tile is very moldy. Yesterday I first let water sit in tub (was able to rule that out as source of leak), then splashed water in corners of tub. Water splashing on interior corner of tub ran down outside of tub, then on to floor.

I'm getting fairly alarmed by this. All of the potential problems/solutions -- ripping up tile floor, reverse sloped tub, etc -- are expensive.

BK-- Let me ask you-- how quickly do you see water after the kids have been splashing?

Bill: Within 15 minutes, possibly less. There was also an obvious water stain on the joists.

I had a contractor out since I posted this. The tub is definitely reverse-sloped about 1/2" toward the faucet end, as is the tile floor. He had two alternative ideas.

1. Put in sliding glass tub/shower door (right now it's just a shower curtain), build it up so water in the track doesn't pool in the "down" corners, redo caulk between tile floor and tub, also redo caulk between tub walls and tub using better quality caulk, total cost about $750, and yell at kid to be careful with water. This is the bandaid fix (he was being honest with me in that all of this will lessen the problem but not solve it)
OR
2. Gut the bathroom, which will probably cost $10K or so.

This is a kid's bathroom; kid is 16 and, I hope, going away to college in about 2 years. It has an ugly 1980s fluorescent light box ceiling and the same coverings & trim I hated in my kitchen -- 3" square tiles with wide grout, brass everything, ugly ratty pickled oak low quality wood vanity -- and a water hog toilet. I'd planned to just do a facelift with paint this summer when we redecorate his room, but now I'm not sure. I really do not have $10K to spend but I also like to know that I am fixing problems, not band-aiding them.

Help!
What would you (Bill or anyone else) do?
Blue

Blue
sorry to hear
same here - it was the chaulking where tub met floor +kiddies splashing
here's what helped
- re-chaulked where tub meets floor
- Make sure the liner curtain is inside the tub & properly drawn - train kiddies
- teaching kiddies not to be splashing lots of water out of tub (they saw where it was leaking onto downstairs ceiling that helped!)
+ this stupid thing was it!
http://www.dslreports.com/forum/r22235814-Keeping-water-in-shower

Btw - back in the day my dad would limit our showers to 5 min! god rest his soul - 9 children, 5 of which were girls!
good luck

Years ago, I had a stain on a ceiling under the upstairs tub where the kids showered.

We finally traced it to the overflow of the tub and if I remember to a small extent the faucet. When the kids would shower, the water would run down the tiled back wall, hit the tub faucet and some of it was getting in the crack where the faucet joined the wall. Also more was migrating through when it would hit the overflow/drain lifter of the tub which wasn't connected properly and allowed the water to just leak into the space.

So try splashing not only outisde of the tub, but run water along the back wall and check your faucet and overflow.

Good luck!

Not that it can be done properly without pulling everything out, but I'd remove the tile floor, waterproof underneath it, and install a new floor. It's not very often that this happens, but it does happen every so often, and when it does, this is the best bet. I still don't think it's the tile (if it were it'd be more of a drip-through that would be noticed over time, not a pouring through 15 minutes later). Water like electricity will find the easiest path following gravity, and I'm wondering if there may be a protrusion in your floor through which the water's going, like baseboard radiator pipes, or water supply lines for the vanity of toilet-- something like that.

Blue, I guess Bill has already given you "expert advise" but I had a similar problem to yours, and relate to your hesitation to do a complete remodel due to big cost, though my situation was slightly different. A water pipe leak underneath my bath floor messed up my bath floor completely. Tiles were laid over plywood over concrete slab, and ply got completely damaged and tiles began to come off, with floor caving in when we walked.

(Since my bath was on 1st floor, leak spread in other rooms underneath the carpet).

The solution suggested was that we only replace the 4.5x5 stretch of the flooring so as to fix the problem. To make it cost-effective, it was suggested that we fix the rotted ply layer and then lay a leno or vinyl tiles etc.

However, the con of this is that, your tub and floor would look quite different for some time until you undertake a project to match it. Besides, to fix the floor, your toilet and vanity will have to come off.

Hope this helps and wish you best of luck in making the decision.

I have this same problem. Can I just polyurethane the tile to seal it

A lot of kids don't know to keep the shower curtain INSIDE the tub while showering! Have had two tenants with mystery leaks, "It only leaks occasionally, when the kids take a shower, call a plumber".... make sure you are caulked up well (should be redone every 4 or 5 years anyway), and maybe even a little corner buffer to stop spray. ALSO: make sure your shower nozzle isn't spraying water out sideways, as happens when the screen gets clogged with grains of (?) and prevents decent flow. Make sure the shower nozzle has been put on with "thread tape", wonder if it was upgraded recently and not done correctly.