Remove mineral tile adhesive completely?

A bathroom floor is to be newly tiled. The mineral tile adhesive has mostly been removed. Is the floor, as seen in the pictures, already sufficiently prepared or does the old tile adhesive need to be completely removed with the grinder?

I can't tell from the pictures. Adequately prepared = floor is smooth. Protruding adhesive residues can be nasty...

Hello "Gerd53". One must distinguish between what gives the feeling of being "sufficient" and what has proven to be a secure substrate preparation in practice (due to many damage cases). Like "Benutzer200," I also cannot see from the photos whether the screed surface was sufficiently pretreated. However, based on practical experience, old cement-based tile adhesives, especially when they have "aged," no longer have their original inherent strength. The same applies to old cement screeds by the way (though without serious consequences). My suggestion is that the subsequent contractor (whatever floor covering is planned next) sands the screed surface intensively. With dust extraction, of course!!! If you want to be sure whether the sanding measure was carried out sufficiently, here is a tip: The technical rule says that the support grain of the screed must be exposed. Then prime and apply a full-surface filler (for an even absorbency towards the adhesive; otherwise, the risk of future hollow spots is quite high). --------------------------------------- Good luck: KlaRa

Thank you for the answers
More precisely:
The floor was ground intensively for a longer period of time with a renovation grinder by an amateur. Grinding disc, see picture. The substrate is now firm. Even the remains of the adhesive are firm.
More pictures that might show the situation better than the above pictures. I hope I am not testing your patience.

Hello "Gerd53". The problem with remote diagnosis is always that even the experts among us cannot make the final decision about whether it was sufficient or not. In the penultimate picture, you can see on the right side that the support grain was exposed during grinding. It couldn't be better! But in the other photos, bright deposits are visible that cannot be assessed. To clarify the problem: If the bright spots are deposits of fine sediments (which occur with new screeds, but this is just an example), this layer might not have had the adhesive bond and inherent strength to ensure the bond between the screed and subsequent layers. I don't mean to scare you with this, nor am I beating around the bush about the truth. If I saw these surfaces myself, I could give an appropriate assessment immediately after a brief inspection. But that is now the task of the following trade. And this assessment as well as responsibility cannot be taken away from anyone! If a tiler is supposed to lay ceramic tiles, he MUST check the substrate. That is the duty of inspection and care of every floor, parquet, and tile layer. Therefore, this note must also mean the end of your inquiry. If the following contractor releases this surface after inspection, then we assume that this is also true from a technical point of view. Otherwise, he (but that is in any case) is liable for consequential damages that arise from his area of responsibility. Regardless of whether amateur installers or professional installation companies! ----------------------- Regards and good luck: KlaRa