I'm fixing one of the bedrooms in my house. While scraping the paint of the interior side of the exterior wall, I found that it has cement board attached to the cinder block wall. The problem is that the cement board moves a bit (in and out) when you press it, and whenever you knock on it, it sounds like it not completely attached to the cinder block. I don't know how the cement board is attached to the wall, since it is covered with a layer of gypsum or join compound. I would like to reattach the cement board with a minimum effort, as I need to have the room ready soon. What's the best way to do it?