Of the many factors that can cause serious damage to historic buildings or works of art (np. wall paintings) biological factors should be mentioned.
Biological processes occur quite commonly as a result of the action of fungi, insects, plants, bacteria, and often animals and birds. The destructive effect of these organisms on masonry materials can be directly or indirectly through other structures.
Mushrooms, mold, insects and bacteria attack organic parts, which may be in the structure of the walls or with which the walls may be coupled (np. wooden anchors, ceilings, roof trusses, etc.).
The spread of the house fungus is extremely extensive. In favorable conditions, pine wood attacked by the fungus loses more than a few months of strength 90%), which can lead to structural failure and catastrophic consequences.
The active action of bacteria and fungi can be recognized not only by the appearance of mold and tarnish on structural parts, but also by the characteristic smell.
The harmful effects of insects on wooden structures and interior furnishings are well known. Need to emphasize, that with prolonged activity of insects, not only the weakening of load-bearing structures may occur, but also damage to masonry systems due to the unfavorable impact of deformed wooden elements.
The destructive effect of insects can even be very harmful to some metals.
Biological attack can also cause rapid decomposition of stones and mortar. A number of microorganisms in favorable physicochemical conditions (temperature, humidity, acid environment, etc.) grows on an inorganic substrate. These microorganisms, as a result of various biochemical abilities, cause corrosion and decomposition of limestone, dolomites, marbles, granites and other mineral materials containing silicates and aluminosilicates.
Biological corrosion most severely damages limestone, marbles and other stones and mortars containing calcium compounds. Various types of microflora willingly develop on the surface of these materials, which produces decomposing biochemical products, as a result, the process of transformation and decomposition of the structure takes place. Need to emphasize, that the activity of microorganisms is multidirectional. Many microorganisms have special adaptive abilities to changes in the environment, very rapid reproduction and expansion.
Plants can also be very harmful, especially grass, trees, creepers and mosses, that entwine or grow on the surfaces of unprotected walls and vaults. Roots, penetrating deep into joints and cracks, by the force of expansion they burst and crumble stones and loosen even the most bonded walls. As a result of this action, conditions are created that are conducive to the penetration of other destructive factors, especially moisture.
The destructive effects of pets should also be mentioned here, especially cows and horses and birds, especially pigeons. Animals contribute, apart from other damage, to the increase of moisture and the release of harmful salts.
Birds, on the other hand, are quite commonly the cause of various types of damage to the architectural decor of buildings, and pigeon manure containing phosphoric acid can have a particularly destructive effect on stones.