ᐅ Removing Old Wallpaper Adhesive: How Do the Professionals Do It?

Hello
Our walls are plastered with lime-cement plaster and were covered with non-woven wallpaper. Since we want smoothly plastered walls now, the old wallpaper needs to be removed. There is still adhesive underneath. Because the walls are rough, this adhesive is not easy to wash off and would be an enormous amount of work given the surface area. I’m also worried that using too much water might cause it to seep down the walls under the screed. How do professionals handle this? Surely no one washes the walls with a small kitchen sponge. Are there machines for this? I had already thought about a steam vacuum cleaner. The wallpaper itself is not the problem; I can remove it easily. But the adhesive is the issue.