Wallpaper – Poor Adhesion Issue Due to Dusty Walls

The existing wallpaper in this sink / vanity room of a hall bathroom is unique, because instead of coming in rolls, it came in pieces of torn paper, each about the size of a paper plate, that were placed on the wall in random ways, with the pieces overlapping each other.  This was a fairly popular wallpaper option back in the ‘90’s. 
I’m to hang new wallpaper in this room, so my first step was to remove the torn paper.  

This started out seeming easy, because the paper was literally falling away from the wall – but only around the top, and only the top 5” or so.  The lower areas were stuck nice and tight to the wall. What’s going on?

The original installer hung his wallpaper directly on new drywall / Sheetrock , with no primer and no other prep.  Turns out that, under this wallpaper, there are actually several different types of wall surfaces related to the new drywall.  

The main part of drywall is grey in color .  But here you see a band of white running along the top of the wall, under the ceiling, about 5” wide.   This is where the joint compound was applied , to smooth over joints , drywall tape , and nail heads . 

But the curious thing is that the wallpaper is adhering to the drywall – but not to this white band of joint compound below the ceiling line.
The reason?  After the drywall guys sanded this area smooth, no one wiped off the dust left over from sanding .  Thus, there was  a layer of dust on the wall, between the wall and the wallpaper.  Well, the wallpaper paste wants to bite into a solid surface, and it can’t get a grip on dust.  That’s why you see this top portion pulling away from the wall. 

I have a lot more prep to do in this room.  But before moving forward, I took a sponge and bucket of water and wiped the dust off that top portion of wall.  Now I’m assured that any smoothing compound or primer or wallcovering or other that is applied, will stick . 

For reference, here’s a shot of the un-primed drywall being uncovered as I strip off wallpaper in another area.  This picture shows the sections of drywall , joint compound , and also paint (from overspraying the woodwork ).  Wallpaper adheres to all these different surfaces in different ways.  Another reason to always use a wallpaper primer – it will adhere to just about any surface, and will create a uniform coating for the wallpaper to adhere to. 
I like Roman Pro 977 Ultra Prime.