Of all the wall surfaces, brick, stone and cement are the most difficult to cover with wallpaper, and it's not recommended by manufacturers or professionals. In MOST cases it is better for you in the short and long term to stay away from attempting to do it. It's not worth the trouble and will not work.
You might find some people saying that wall liner is the best solution to cover up walls made with brick, stone, or cement but ask any experienced paperhanger and they will tell you to even stay away from that supposed solution. There are two main reasons.
Lots of Small Indentations
Brick and stone are porous by their very nature. You cannot had a primer that will stick on top of them and no wallpaper paste that we know will work long term.
Lines With Show
Brick and stone are again, by nature, very bumping and rough, all of which will easily show through the wallpaper. How is the installer going to smooth our bubbles? We have seen people try to do this and the end result is not pretty.
If You HAVE To Do It Then You Must Even Out the Surface
The first thing you will have to do is make the surface more even. Typically, this is much easier with brick than stone because bricks start with a more even surface. You will need to apply mortar or other filler between the gaps and smooth uneven areas. Be careful with stone since it can be difficult to soften harder edges. Sanding is recommended, which will mean a lot of dust. You will need to cover your room and move out anything that does not have to be there.
Another way to even the surface is to install 1″x2″ strips of wood to the top and bottom of the wall. Then you can install a heavily textured wallpaper to those strips of wood, overlapping each seam. It won't look perfect, in fact, it will look like a fabric wall, or curtain, but it will be extremely easy to remove at a later date.