I have just moved into an old georgian house, around 200 years old, and iwas going to hang a heavy duty mirror. When i drilled through the old plaster, I hit some air then quickly hit a very 'rubbery' material that bounced the drill bit back a bit.
Does anyone have any idea what this could be? I was drilling into a wall that was alongside a window and would have later been brick (at a much deeper point).
Im unsure if i should force it on or relocate the hole. Does anyone have any ideas?