We've used them here with the same walls. Stud finders work by sensing the difference in the density of the areas it is moved over. When it's over a stud, the area is denser than when it isn't, and the difference shows up on the readout. Whether your wall board is plaster or sheetrock shouldn't matter. They are a little more sluggish to give you a readout, so you need to move the finder more slowly over the plaster wall while searching than you would with sheetrock.