One aspect of the disclosure is a plaster board having a first edge and an opposed second edge, and a third edge and an opposed fourth edge. The plaster board includes a first layer of hardened plaster material including a first surface and an opposed second surface, and a second layer of hardened plaster material including a first surface and an opposed second surface. The second layer of hardened plaster material is stacked against the first layer such that their first surfaces face one another. The first layer and the second layer together define the first, second, third, and fourth edges of the plaster board. The plaster board also includes a viscoelastic polymer disposed between the first surfaces of the first and second layers of hardened plaster material. The viscoelastic polymer does not extend substantially to the first, second, third, and fourth edges of the plaster board.