preparation of nor board for vinyl flooring
You have the subfloor now you need to lay the underlaymant.
It needs to be at least 1/4 thick, sanded and underlaymant rated.
DO NOT USE LOUAN!!
Do not use any glue under it, do not have the seams line up with the seams below, do not nail it into the floor joist below.
I use a narrow crown pneumatic staple gun to install mine.
If you use underlaymant nails you have to go back and use filler to fix all the flaws, hammer marks and the seams.
Any flaws will show right through the flooring.