What are the factors of destruction of stones? (Reasons of damage and deterioration of stones) Part 2

The effect of wind on the destruction of building stones

Since the wind carries the dust particles, the wear caused by these particles destroys the rocks. Erosion is more common in areas with stronger winds and more dust particles in the air.

Temperature changes and expansion and contraction of rocks

Expansion and contraction caused by frequent temperature changes is another factor in the destruction of stones over time; Especially if the stone is composed of several minerals with different volume expansion coefficients. This factor causes a lot of damage in areas with severe climate changes.

Stones such as travertine have acceptable resistance in harsh weather conditions such as cold, heat and severe frosts. (Of course, it should be noted that the resin and processing operations have been done correctly on the stone)

Rock mud, the main cause of limestone destruction

Mudstones destroy limestone but act as a protective coating for other rocks and prevent their deterioration. Marble and marble have the highest amount of lime and are very vulnerable to stone mud.

The effect of acids on stone destruction

In general, anything that is not pH neutral will damage your stone in some way. This includes any natural, synthetic or homemade product that contains any acidic or alkaline substances such as lemon or citric acid and acid rain.

Strong mineral acids such as sulfuric acid, hydrochloric acid, hydrofluoric acid, etc., should not be sprayed even a drop on the stone plate, because it causes corrosion of the stone and makes the desired surface out of smoothness and uniformity and makes it cloudy, which itself It causes disruption in working and also makes it harder to clean the work surface. It is also possible for chemicals to remain in the created holes, which over time will cause the destruction of the stone.

(Granite is said to be resistant to most acids, except for hydrofluoric acid, which is found in small amounts in some stain removers and cleaners. But if the granite contains calcite, serpentine, onyx, or other calcareous minerals that react to acid are sensitive, you may find cloudy spots on polished granite surfaces.)

The results of the stone durability test in sulfuric acid and nitric acid solutions show that stones with non-carbonate composition are resistant to these solutions and stones with carbonate composition are resistant. (Nikodel, M., and Jamshidi, A., and Hafzi Moghadis, N. (2019). This test was performed on 14 samples of different Iranian stones.

Microbiological or vegetative growth

The roots of plants and weeds that grow between the seams of the stone cause moisture in the stone and secrete organic and acidic substances that lead to the disintegration of the stone. Dust particles of organic or inorganic origin may also sit on the surface of the stone and penetrate into the pores of the stone. When these materials come into contact with moisture or rainwater, the bacteriological process begins and acid-producing microorganisms attack the stones, causing decay. It appears that under certain environmental conditions, attack by microorganisms can be a serious problem, but evidence suggests that growth of microorganisms usually occurs in rock that has been partially degraded by other processes.

Contact and human interventions

This is more important in historical buildings; Due to people’s increasing interest in historical structures, the impact of human contact on stone surfaces as well as other building materials has become a serious concern. For example, stone floors are gradually worn down by foot traffic. The stones are damaged by people who plunge sharp objects into the soft stone in search of engravings and souvenirs, and the removal of wall paintings has become an important maintenance problem.

Original construction and bilateral decay

The durability of stone structures largely depends on the factors that were observed in their initial construction. When different types of stones are placed next to each other and have a contact surface, mutual decay occurs. For example, when sandstone is used under limestone, the chemicals that are transferred from the limestone by rainwater to the sandstone cause its destruction.

Also, the use of steel and cast iron parts, roll plates, reinforcing bars, etc. are often used in the construction or repair of stone structures and building facades, while some of these metals are prone to corrosion, which can lead to cracking. And the crust becomes stone. Therefore, non-corrosive materials such as epoxy-coated steel, special types of stainless steel, or non-corrosive non-ferrous alloys should be used in construction.

Rainwater passing through the surfaces of copper and its alloys, after reaching the limestone, can cause green spots on the stone and destroy it. It is very difficult to remove rust and stains from stones with high porosity. The expansion of iron and steel corrosion inside the facade has the greatest effect on the destruction of stone, for this reason, all metal parts used in the facade must be rust-proof and stainless steel.