As long as there are not structural cracks in the concrete floor you can install porcelain tile over it.
Can you install tile over painted concrete floor.
You need to prepare by removing the paint and scarifying the surface to open up the pores of the concrete.
Even though nothing may happen nobody has a crystal ball and the track record of tile over painted floors is not great so he is basing his decision on historical data.
Painted concrete can be made porous with sandblasting or other hard abrasive actions.
No big deal hack or grind the epoxy coated surface to form keys and tile over.
As long as the paint is down well and not flaking you can go over it with some preparation.
The tile installer is right.
The thinset will probably bond to the epoxy floor.
Unfortunately the tile cannot be adhered directly to the painted surface.
You want water to readily absorb into it.
All paint will need to be removed before you begin installing the tile.
If you use a stripper to remove the paint be sure to flush it thoroughly to remove any residuals.
Paint used on concrete will not bond with the tile adhesive.
However you should remember this one instruction no.
Sheets of cement backing available from most do it yourself.
But there is a solution to the problem.
Before you lay any sort of tile whether it is stone ceramic or peel and stick vinyl you must prepare your concrete floor to ensure that the tiles will go down properly and stay where they re.
Sand or scuff it up well and wash to get.
While you can install tile directly on concrete problems erupt when the concrete cracks or shifts.
Once the concrete floor is paint free the tiling process is similar to most other floor tiling jobs.