To properly install a new tile surface you should remove the existing vinyl tile grind down as much of the old tile adhesive as possible and then apply the leveling compound to smooth out the surface for the new tile.
Can hardboard be place on top of vinyl tiles.
It can be confusing because many leveling compounds are marked as useable on a variety of surfaces including linoleum and vinyl.
2 loose lay the first board over the centre with its long edges at 90 degrees to the floorboards.
3 adjust it so that the edges do not correspond with the gaps between the floorboards.
Two layers of 5 8 plywood at least then use cement board.
Surely ply has better moisture resistance.
Fill low spots on the floor with patching compound applied with a putty knife.
If your flooring is already thick enough needs to be stable to prevent cracking later.
4 loose lay more boards up down and across the room.
Hardboard is a very poor poor product to use for preping a subfloor.
Stir ready to use floor patching compound with a paint stirring stick.
I was planning on using 6mm plywood for a solid base for vinyl although i see most websites recommend hardboard.
How to 4 laying hardboard and plywood 1 use a chalk line to mark two lines at 90 degree angles to each other across the centre of the room f2.