A few on here used the dreaded Rawlplug tool , including me . I 've told this on here before , but as an apprentice we were installing lighting on a new multi storey ar park in the city , Holiday Street , actually. After chalking a line we would sit on top of the steps , plugging the concrete ceiling for conduit saddles ....one day we could hear this strange , reverberating sound coming up from the lower floors ..... one of our guys comes up saying the sprinkler guys have got these drills that" hammer into the concrete , Hilti or something , you've never seen anything like them "