Five main culprits that damage stone

(Many great historical monuments around the world are made of stone. Despite wars and long periods of historical change, thanks to the natural properties of stone, they still showcase their beauty today. The image shows the Parthenon temple in Greece.)

 

Stone is one of the relatively high-end materials in the field of interior and exterior decoration. Its pure natural textures and patterns, combined with various surface treatments, can elevate the decorative effect of both interior and exterior spaces. Compared to other decorative materials that are difficult to clean once stained or easily shattered by heavy impact, stone is significantly more practical. It is not only structurally strong and resistant to heavy impacts, but also has a smooth surface that resists general dirt and stains, making it a highly cost-effective decorative material.

 

 

However, this doesn't mean that stone is invulnerable. In the practical application of stone, there are still many destructive factors in the environment that can cause erosion. Therefore, don't assume that simply choosing stone as a decorative material means you can neglect its maintenance. To extend its lifespan as much as possible, we still need to understand the destructive factors that affect the lifespan of stone and perform corresponding maintenance.

 

 

In the eyes of the general public, water is the source of life, but for those working with stone, water is, to some extent, the root of all evil. Because water is the most difficult substance to eliminate in daily life, various stone products are relatively susceptible to water erosion in many details, leading to a variety of problems. The root cause of many common phenomena is often water. Water carries oxidizing or reducing minerals and salts into the stone, and also introduces various modern industrial pollutants, thus accelerating the dissolution and destruction of the stone. This can lead to the loss of calcium carbonate and other components, causing the stone to lose its luster; or the formation of gels inside the stone, resulting in water stains; or the migration of calcium components to the surface, causing whitening; or the rusting of iron in the stone, resulting in rust stains.

 

On the other hand, rainwater, condensation, and groundwater enter the stone through micropores. With changes in temperature, the stone repeatedly contracts or expands, and the resulting stress can cause cracking and damage. This is especially true for outdoor stone exposed to humid environments and significant diurnal temperature variations. The repeated, uneven absorption, penetration, and dissolution of water, along with continuous contraction and expansion, can easily cause the rock to crack. Furthermore, in colder climates, such as in northern regions, when the stone's capillaries absorb sufficient moisture, and the temperature drops below 0°C, the water in the stone freezes and expands. When the expansion force of the ice exceeds the structural strength of the stone, damage occurs; this is known as freeze-thaw damage.

 

It is also worth noting that water is an indispensable condition for the growth of microorganisms and other organisms. The growth of microorganisms can also cause significant damage to the stone.

 

 

Natural stone inherently contains salt crystals during its natural formation process. After being mined and processed, the salt crystal content may increase due to the penetration of cement, mortar, dust, moisture, seawater, and polluted liquids into the micropores. On the one hand, salt generates significant pressure during crystallization, and if the stone's temperature rises significantly, the salt will expand in volume. On the other hand, under certain conditions, some salts can recrystallize to form new hydrates, occupying a larger volume and generating greater pressure. These situations can all lead to internal damage to the stone.

 

In typical usage scenarios, the damage caused by salt crystallization to stone is often exacerbated by wind. Salt crystals inside the stone dissolve in water (moisture) and diffuse to the surface. Wind accelerates water evaporation, thus promoting salt accumulation and crystallization. Repeated salt dissolution and crystallization can cause the surface of the stone's micropores to flake off in a powdery or scaly manner. If washed by rainwater, over time, deep grooves can easily form on the stone's surface, affecting its aesthetic appearance. Furthermore, some decorative stones exhibit a phenomenon of constantly damp surfaces that never dry. The reason for this is often the hygroscopic effect of salts. This is something we need to pay close attention to in our daily lives.

 

 

 

From ancient China to ancient Babylon in Mesopotamia, to ancient Greece, Egypt, and Rome along the Mediterranean coast, humanity's long journey from barbarism to civilization has left behind a vast legacy of stone artifacts. As a result, many great stone buildings and sculptures around the world have been preserved to this day. However, the details of most of these relics are now stained and blurred, and the culprit is acid rain.

 

The combination of carbon dioxide, sulfur dioxide, and other oxides in the air with rainwater increases the acidity of the water, making it more corrosive. This acidic liquid is extremely damaging to stone, especially carbonate stones. When acid rain falls, the calcium carbonate in the stone reacts chemically with the sulfur dioxide in the acid rain, producing calcium sulfate. Some of the calcium sulfate enters the gaps between the stone grains, depositing on the surface of the marble in the form of a crust, which then gradually peels off, affecting the stone curtain wall. The remaining soluble salts may further corrode the stone through recrystallization or hydration.

 

 

 

Smog is a mixture of moisture, dust, and various combustion products from chemical fuels. The smoke and dust act like a sponge, absorbing various gases, and when mixed with water, they form an acidic solution. Severe industrial pollution, vehicle exhaust emissions, and stagnant atmospheric circulation are the main causes of industrial smog. Smog is not only harmful to living organisms but also causes significant staining and corrosion of stone buildings and decorative stones.

 

 

 

 

Generally speaking, the erosion of stone caused directly by biological organisms or their metabolites is much less significant than that caused by other destructive factors. However, the erosion and damage to stone caused by biological organisms, especially microorganisms, should not be ignored. The products of biological metabolism, including oxygen, carbon dioxide, and organic acids, dissolve in water and increase its corrosiveness. Simultaneously, during the process of organic matter decomposition, organisms promote redox reactions of minerals and consume minerals, thus accelerating rock decomposition. Additionally, the excrement of animals such as birds can also cause damage to stone.

 

 

Unprotected new stone surfaces are often more easily colonized by organisms such as algae, bacteria, and lichens. Once these organisms occupy the stone surface, biodegradation continues to penetrate deeper, causing irreversible damage to the stone. Furthermore, some plants, such as Virginia creeper and ivy, can grow into cracks in the stone, directly causing stress damage.

 

Of course, the various factors leading to stone corrosion are not isolated; they occur simultaneously and mutually reinforce each other. Therefore, in practical applications, we need to carefully analyze the local climate and geological conditions and adopt the most appropriate methods for stone maintenance to prevent erosion.