I have plastered walls. The plaster board has a foil backing for insulation purposes.:furious::furious::furious:
You dont know what the fk you are talking about go back to school stud finders will work on ceilings.Use them every day and works every time:furious::furious::furious::furious:
In case you're interested, its name is an 'awl'.Once you find your "lumber" through the drywall I always get a "poker" (I'm not sure exactly what it's called... it looks like a screwdriver with a sharp point.) Anyway, use it to map out the "lumber" so you're dead on the center. I do this when I install heavy plasma tv's. Once I find the stud I poke holes until I find the edge of the stud... then go the other way until I find the opposite edge. This way you know for sure you're screwing into the center.
(simple putty fills the holes when done)