Determine whether you have plaster walls or drywall by doing one of the following: Insert a thumbtack in the wall. Drywall is soft and will allow the pin to push through with minimal effort, while plaster walls are more rigid and difficult to pin without the help of a hammer.  Feel your wall. Plaster is harder, colder, and smoother than drywall. Tap on the wall. Drywall sounds hollow, while plaster doesn't.  Plaster walls are typically found in older homes, so your home's age can also be a helpful indicator.