Glue ir nail ply under laminate

[john4703]

I am planning to lay laminate over some old floorboards. I’ve got thick underlay but feel that as there are gaps between the boards and broken edges where they have been lifted and re-laid I should first cover them in either hardboard or 6mm ply.
I would appreciate advice about which is best to use, ply or hardboard.
Also can I use something like ‘no more nails’ to glue this to the old floorboards? That would seem simpler and quicker than nailing it down.

 

[JohnD]

consider ripping up those tatty, cracked, broken old boards and laying a new floor in 18mm WBP ply, screwed down.