It can be placed over it, but first, you must do an analysis of the adherence of the old coating. If they sound hollow when tapped or are coming unstuck, it is better to completely remove them.

 

In the case of perfect adhesion, do a heavy cleaning in the place eliminating dirt such as wax, paintings, mold, etc., and wash with plenty of water.

 

For gluing, use mortar adhesive suitable for laying new ceramic over old ceramic.

 

Only lay ceramic over ceramic with joints, even on rectified. There is a protractor on the market for: registers, boxes and door frame and recessed windows finishes to compensate for the difference in height. An inclined sill can be installed to avoid stepping on the doors.