How can we effectively clean the plaster to prepare for furring strips and drywall installation, and is there a product to seal stubborn adhesive remnants to prevent future issues with paper layers?
So, we have this old 1949 cement block house that we’re trying to spruce up. The exterior just has some faded paint, and inside we’ve got layers upon layers of wallpaper and drywall. We’ve managed to strip everything down to the original cement-like plaster, but there’s this one stubborn layer of wallpaper that just won’t budge. We’ve tried water and brushing, but it’s just making a mess. And we can’t scrape it off because the plaster isn’t smooth. The heat source is this old crude oil system, so there’s black dust on all the walls.
We’re planning to fur out the exterior and add siding soon, but right now we’re just feeling a bit overwhelmed by the interior. How clean does the plaster need to be before we can start adding furring strips and hanging drywall? Is there some kind of product we can use to seal the stubborn wallpaper residue? And will leaving some paper behind cause issues in the long run? 
I need to cancel my appointment for tomorrow.
I tried looking online but couldn’t find a definitive answer about my specific materials and the climate. I’m used to living by the coast, where everything is impacted by moisture. Now I’m adjusting to this desert climate.