Quote Originally Posted by PoolDoc View Post
I can offer one bit of advice that applies to painting, re-plastering, AND applying tile: no surface is better than what's under it. If you don't have a sound surface under your tile, you'll never have a good tile application!
That sort of covers it.

Whether a sound subsurface requires removing everything or not can't be determined from here -- not even with photos! But, if you want to be 100% certain, then removing everything won't hurt.

The difficulty may come if you find rotten gunite under bad plaster. In many pools, you have to make choice between patching and complete replacement.