asloudasitgets

i recently changed out my front door bell. well when i went out to change the frint door bell, i noticed that the one i bought needs space inside the wall so that the connection to the wires can fit, and that the button sits flush against the house. so i took a chisel and took out some of the cement to let the button fit. remind you the old one had its own casing so it would just sit on top of the wall. Well when i was chiseling some parts just gave way and now the mounting screws have to where to be drilled, and i cant ree drill it somewhere eles cause of the big hole. I noticed also when i took the old one iff it was just stuck on there with some white rubber glue of some sort?

does anyone know what it is? maybe i could just glue it on cause i have nothing to screw into. or maybe some filler i can use to let dry then i can srill into?