We are going to be painting our dining room and after we scraped the wallpaper down and washed the glue off of the walls we noticed around the thermostat that there is an open area where you can sort of see the wall behind it. It looks concrete-like which leads me to believe it may be plaster walls. My house was built in 1956 and the rest of the walls in the house are drywall so I am not sure why this room would be plaster or if its plaster. It is not an addition or anything. Can anyone tell me how to identify this? We are looking to install a chair rail and are leery to do so if it is plaster walls. Thanks!