Anyone got opinions on what could be going on here? Drilled in with masonry bit, goes through initial later of plaster easy enough, hits something harder, the suddenly gives in to what feels hollow. Also sounds hollow when knocked on. Was going to use plugs to hang a curtain track but seems like stone kind of plasterboard fixing might be more suitable.
Anyone got opinions on what could be going on here? Drilled in with masonry bit, goes through initial later of plaster easy enough, hits something harder, the suddenly gives in to what feels hollow. Also sounds hollow when knocked on. Was going to use plugs to hang a curtain track but seems like stone kind of plasterboard fixing might be more suitable.
Context: Victorian house above bay window