Mortar is a workable paste used to bind construction blocks together and fill gaps. It is typically made of sand, a binder like cement or lime, and water. Mortar hardens after setting to form a rigid structure. Different types of mortar are used depending on the binder, intended use, and required properties. Cement mortar provides high strength and is used for load-bearing walls. Lime mortar is used above ground, while mud mortar is a cheaper option for ordinary buildings. Special mortars include fire-resistant, lightweight, and sound absorbing varieties.