Remember, water
will find a way.
When you see mildew or loose tile, the damage is usually done.
It's sad, the contractor's license board only requires projects to last 10 years. Mastic over greenboard will last 10-12 years. Only problem is after it fails you have to pay to have it demo'ed, fix the rot and then rebuild.
I'm serious, a mortar prepared project will last over fifty years. I tear them out only because the yellow and green, pink and gray tile jobs of the '50's make people
.
No water damage behind those jobs.
KT