I am prepping to install about 1300 sq ft of porcelain tile on concrete, where currently there is some old tile + carpet. I plan on taking up the old tile with a floor stripper + the carpet. There is a problem area with the current tile where it appears the thinset or mastic or whatever was used didn't properly adhere to the underlying concrete, because the existing tile and thinset or mastic or whatever they used is coming up in a few spots fairly easily, just chipping off like it never bonded.

So my concern is something happened during the original install (14 yrs ago) to cause it to not bond, so I'm thinking once I strip down to the concrete, I should acid etch ir or something to help the new thinset I use to adhere.

Is this really needed? I plan on using some thinset with an included "bonding agent" in it. But I've used acid etching before to help other things stick to concrete (such as sealant on a concrete pool deck) so I'm thinking a little acid will roughen up the surface, esp. since it is now 14 yrs old and could use a little.

My other concern is this is a condo on the 7th floor. If I *do* do the acid, where do I drain the used acid/water combo? Presumably the acid won't 100% neutralize, so I don't want to suck the solution into any machine like a shopvac which would corrode any metal parts, and I can't flush it down the drain or over the balcony into my neighbor's furniture or metal railings, etc, etc.

Any other options? Is this just overkill? TIA!!