Of all the wall types, brick and stone are the most difficult to cover with wallpaper, and it usually is not recommended. It is not something that most people consider because brick and stone are not often used within homes. However, it is not completely unheard of. Perhaps you do not like the look of the brick or stone on your fireplace or you are enclosing part of the exterior of your home. In these instances, you may be looking for an easier way to remodel than to tear the wall down and start from the beginning.
Honestly, the best solution is to find a veneer to place over the brick or stone. You can change the look and texture without having to do a lot of additional work. There are a wide range of options and plenty of instructions online. The process can be time consuming, but the end results are often amazing.
Going with Wallpaper
If you do not find a veneer you like, or if you have your heart set on a certain wallpaper, you can apply it over brick or stone. Just be aware that you will need to dedicate a considerable amount of time to the job (up to a few days). You will also need to be prepared for some serious cleanup.
Even 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. You may want to cover the doors to the other rooms in the house too.
Adding the Wallpaper
Once the surface is smoothed, you can begin hanging the wallpaper. Anything applied over brick or stone should be made of a much stronger material than the average wallpaper. Called bridging material, it is designed to make rough surfaces smoother. This is the first layer.
The second layer is the wallpaper itself. With the grooves and edges covered, you can finally apply the desired wallpaper over the bridging material. Keep in mind that you may not want wallpaper applied too close to the fire. Not only is it a potential hazard, it is likely the fire will cause blacking over the wallpaper directly above it.