The causes of too rapid destruction of historic brick buildings have their source in the use of impermanent and inappropriate building materials, in faulty execution, inaccurate or incorrect static assumptions, in inappropriate construction solutions, as well as in the erroneous assessment of the natural features of the land.
Strength and durability of masonry structures, especially those under active load, depends on the quality of the materials used, the strength of stones or bricks, mortar strength and adhesion, binding method (thread used), joint thickness, the quality of workmanship and the correctness of the construction solution.
According to modern technical requirements, the method of bonding used should ensure a permanent static balance of the system, regardless of mortar cooperation. In addition, the structural solution of the walls, pillars etc. masonry elements must not allow condensation of water vapor inside the structure or on its surface to an extent detrimental to the durability and strength of the structure itself, as well as human health and property safety.
As can be seen, previously erected masonry structures often differed from the above-mentioned technical conditions, especially stone structures.
Layers are intertwined in stone constructions, composed of materials with different mechanical and physical characteristics, often with natural defects. Therefore, the structure of the walls in cross-section is heterogeneous. Individual stones in the wall work unevenly and have different resistance to static deformation and destructive factors. It is also characteristic, that in many cases, in the initial period of construction, when shaping masonry structures, the principle of using the inherent properties of materials was not followed, improperly worked stones were used, binding regularity was not observed, filling joints with mortar, bringing the face to the vertical. These fundamental defects of the systems were covered with mortar: hence the considerable thickness of the joints and plasters.
Brick masonry structures were made much more correctly in terms of bonding behavior, but also here, both in the cross-section of the walls, as well as in the facing parts, bricks of different quality are found. In addition to well-burnt bricks, bricks with production defects in the form of large and hairline cracks were used, resulting from drying and firing as a result of improper mixing and fragmentation of the raw material. These structural defects of brick materials facilitate and accelerate the process of destruction.
In the old masonry structures, both stone, like brick, there is no horizontal damp proof insulation between the foundation walls and the walls of the upper part of the building, nor vertical insulation at the contact with the ground of the walls of the basement rooms.
In many cases, irregularly running channels are found in thick walls, cavities and grooves, as well as unfilled spaces left by decayed wooden anchors and other structures.
In some systems, the lack of a proper transition can be found when changing the thickness of the walls (no faults, faults too large or undercutting the face of the wall). Frequent structural defects include dry jointing of longitudinal and transverse walls, as well as incorrect solutions of door and window openings, especially the overhangs.
In addition to the factors described above, the most dangerous are defects in the method of foundation and defects in the structure of the foundations themselves. Errors in the construction of foundations are mainly due to insufficiently selected ground pressure surfaces or too shallow foundations. Most often, this is due to the wrong recognition of the type and quality of the soil. There are also cases, that the shallower foundation occurred as a result of later shearing of the layers of the land surrounding the building due to its regulation or even erosion. In the past, much attention was paid to the construction of foundations in general, however, there are failures caused by the foundation of the building on the preserved old underground structures, that have been deformed.
Structural defects in brick historic buildings can often be found also in the incompetent use of vault cross-sections, arcade, lintels, supports and load-bearing walls. In the case of excessive deformation or cracking of the vaults and arches can be noticed, that displacements occur in the supports as a result of increased strut values, delamination of joints, scratches and general weakening of spatial bonds. A similar phenomenon may occur in the case of flat covers, if their cross-section is not adapted to the span and load.
Serious damage to the maintenance of historic substances can also be caused by construction errors resulting from ill-considered conservation actions. The introduction of irrational structures or the use of layouts has a particularly negative impact on the durability of historic buildings, which not only do not contribute to the strengthening of the building, but on the contrary, they become the reason for disturbing the balance of the existing structural system.
A considerable share in making wrong or dilettante conservation decisions are made superficially and without due discernment of technical expertise.