The object of the present invention is a mortar for buildings that contains foamed polystyrene and cement. The mortar contains the foamed polystyrene and a part of the cement in the form of a ground material and it contains 50-200 kg of unbound, anhydrous cement for every 1 m3 of ground material, where the ground material includes granules of 0.5-10 mm and is made by grinding pressed foamed concrete that has been allowed to stand and contains foamed polystyrene. For the production of the mortar, the pressed foam concrete that has been allowed to stand and contains polystyrene foam is ground into granules no larger than 10 mm, cement is added, then water is added thereto upon application.; Such mortar can be used to create various building structures that include a frame structure (40), a foam concrete panel (60) affixed to the frame structure (40) and mortar (14) applied into the interspaces of the frame structure (40).