Causes of cracks in the plaster of unheated stone buildings

Abstract

Introduction. The objects of the study are unheated stone buildings. Most of them are historical, including cultural heritage sites. The subject of the study is the analysis of the causes of cracks in the inner plaster layer. Damage of the internal plaster coating has a strong influence on the condition of wall paintings and artistic decoration of the exterior walls of preserved historical objects of cultural heritage. There is a lack of systematic studies of the causes of the damage on the walls. The scientific novelty of the work is the development of a finite element model. In this model, a fragment of masonry is considered together with a plaster coating. The practical significance of the study is to establish causal relationships between damage to load-bearing stone walls and internal plaster coatings. The study is aimed at identifying the most significant factors and impacts that influence the appearance of damage in the inner plaster layer of unheated stone buildings and religious buildings.
 
 Materials and methods. A detailed analysis of the stress state of the plaster layer during the course of shrinkage deformations in it was performed. Numerical research methods based on a finite element model of a fragment of masonry with a plaster layer were used.
 
 Results. The paper provides a graph of the dependence of the main tensile stresses on the ratio of the modulus of elasticity of the plaster mortar to the modulus of deformation of the masonry. With an increase in this ratio, the values of the main tensile stresses increase linearly. When they reach a value of 1.0 MPa, they become comparable to the limiting stresses at which a crack is formed. The obtained results are of great practical importance in the development of programs for the inspection, repair and restoration of historical cultural heritage sites.
 
 Conclusions. It is established that the values of the main tensile stresses practically do not depend on the thickness of the plaster layer. Humidity deformations of the plaster layer significantly exceed temperature ones and are the most significant factors for the appearance of cracks on the internal plaster coating of external walls in the absence of force cracks in the walls.