I want to install a hard click vinyl floor over an old hard adhesive cork floor. The height of the new floor should be 4mm so it doesn't build up as high. Now, I've heard that you should only install 10mm thick vinyl flooring on HDF board on cork floors because cork is supposedly too soft. This is not true, at least to the touch: no matter how hard you press with your finger, nothing lends itself.
What are your recommendations/experiences? Pulling out the old cork is not an alternative.
We installed vinyl hardwood flooring directly floating on our old cork floor (glued down, about 5mm thick) about 5 years ago. We haven't had any problems so far, and the cork is extra good soundproofing.
Laying "PVC click vinyl flooring" over the old cork top layer is, of course, an unusual special design. It should be, because there is no fixed connection between the different types of flooring (i.e. gluing), and puncture under the action of point loads (new PVC flooring) can not be feared due to the self-sufficiency of its supporting layer HDF. Only the overall height of the structure should be uniform, so that the doors do not overstretch and do not create a danger to neighboring rooms.