If you're planning on hanging something on your walls -- whether you have plasterboard or plaster -- most directions will tell you to hang the item on a stud. Studs are vertical wooden beams that are a part of the wall frame. The plasterboard or plaster is placed over the studs. Although you can easily use a stud finder to find the studs in plasterboard walls, you cannot use most stud finders with plaster. Instead, you have to rely on a much more primitive -- but just as accurate -- form of stud finding.
Knock on the wall -- starting at the far left of the wall -- moving slightly to right. When you knock, it should feel and sound hollow on the other side. This is the area between studs.
Move slowly to your right while gently knocking on the wall. When the wall feels harder and you hear a dull sound while knocking, you have located a stud. Place a mark on the wall with a pencil to indicate where a stud has been found.
Continue moving to the right and knocking on the wall until you encounter the next hard wall area. Place a mark on that stud as well. Do this until you've marked all of the studs.
Measure the length between each stud. Typically, the studs are 40 cm (16 inches) apart.
Tap a nail into the wall where you have placed a stud mark. If there is some resistance, you've lined the nail up perfectly with the stud.
Keep in mind that most electrical sockets are mounted to the stud. If there is an outlet on the wall, start at that point (using the knocking method) moving right, then left, away from the electrical line.