During the restoration of historical buildings, it is very important for the maintenance of the authenticity of the building that decisions related to the selection of materials and the plaster mortar mixtures, determined through plaster analyses, are in accordance with those of the historical structure. In restoration of the historical buildings, there are also some important parameters related with interior room acoustics such as propagating sound properly, ensuring speech intelligibility, preventing from undesirable interior noise and maintaining of auditory comfort conditions. The present study investigates how the sound-absorption coefficient of existing plaster layers can be increased and describes the means of ensuring the newly applied plaster layers are in accordance with the historical structure. Within the study, three different plaster mixtures containing three different type of binder, with plaster layers of 3 cm, 6 cm, 9 cm and 12 cm thickness were produced with each mixture type. The sound-absorption coefficient tests were carried out according to mixtures type and plaster layer thickness. The sound absorption coefficients were modeled using MATLAB software for different plaster thicknesses based on the results obtained from the sound-absorption coefficient measurements. In following stage, to show the effect of the measurement results of the sound-absorption coefficient within the place, a historical place was selected and reverberation time analyses were carried out in the direction of the measurement results. In this research, it is demonstrated that the sound absorption can be increased by means of increasing plaster layer thickness and changing mortar mixture types. It is concluded that the sound absorption research for historical buildings systematically carried out in order to show the role of importance sound absorption material selection in accordance with historical plaster analysis in restoration process. (C) 2018 Elsevier Masson SAS. All rights reserved.