Among the many marbles, white marble is undoubtedly one of the most widely used stones. White marble is used in high-end and luxurious walls, floors, background walls, stairs, countertops, etc.
The simplicity and elegance of white marble, noble temperament, softness and delicacy are really addictive, and the decorative effect is even better, which is simply fantastic. Its mild tones, white snow, and pure beauty like snowflakes allow many designers to make full use and display. But at the same time, it is also the most loved and feared variety. However, white marble is hypocritical, fragile, and difficult to serve in terms of anti-fouling, which makes some users regret it, especially the fact that white marble is easy to turn yellow, which makes many people love it. Users of white marble stay away. In order to solve the quality problems such as white hair and yellow hair, we have to analyze the internal and external factors, thoroughly understand the nature of marble, and the root cause of the quality problem, and then we can solve the fundamental problem. So what causes white marble to turn yellow? How to keep the original appearance of white marble? We will help you!
Causes of yellowing of white marble
The structure and composition of the white marble stone itself
Scanning electron microscope studies on the surface of the most common white marble found that iron minerals with particle sizes ranging from 2 microns to several hundreds of microns exist on the surface and texture of white marble, some of which are distributed on the surface of the plate, and some are enriched in the surface. texture. The oxidation of iron minerals contained in white marble is considered to be the main reason for the yellowing of marble. Since most marbles have a single and uniform color except for the texture part, when the iron-containing minerals randomly dispersed in the marble are oxidized to form yellow or brown hydrated iron oxides, defects on the board surface are formed, and the aesthetic feeling is stains, especially for white marble. The iron in white marble slabs mainly exists as ferrous sulfide, iron carbonate and magnesium iron silicate. These iron minerals are dispersed in the marble matrix or enriched in the marble texture. When these ferrous minerals on the stone surface are oxidized by oxygen in the air to form ferric iron and combine with water to form hydrated ferric hydroxide, what we often call rust is formed, commonly known as spit yellow. If no protective measures are taken, this phenomenon of marble spit yellowing will appear 8-12 months after the marble is placed.
An interesting phenomenon is that this phenomenon of yellowing does not occur for marbles placed next to a heat source, such as a hot water pipe, which shows that the yellowing phenomenon of white marble is closely related to water. However, contact with water does not necessarily lead to yellowing of white marble. The thermal shock test on white marble shows that the stone samples are placed in deionized water at 15-25°C for 6 hours, and then the samples are placed in an oven at 100-110°C for 18 hours. After 20 such cycles, it was found that only the surface iron-rich samples exhibited a slight yellowing phenomenon, which was much lower than the natural yellowing phenomenon. This experimental phenomenon shows that the oxidation-reduction reaction of ferrous iron to ferric iron proceeds very slowly due to the very low conductivity of deionized water. Therefore, although the sample was immersed in water for a long time and circulated for many times, there was no obvious yellowing phenomenon. This test result shows that the yellowing phenomenon of white marble is the result of the combined action of oxidation and hydration on the ferrous minerals on the stone surface, and these two conditions are indispensable. Unlike soaking in ionized water, white marble soaked in alkaline solution is very prone to yellowing. The same stone samples were placed in alkaline water at 15-25 °C for 6 hours, and then the samples were placed in an oven at 50-60 °C for 18 hours. After 20 such cycles, the test found that all white marbles selected for the experiment had yellowed, with Carrara white being the worst. The alkaline solution is easy to make the white marble turn yellow, because in the alkaline medium, the redox potential of ferrous iron is reduced to ferric iron, and it is easily oxidized to ferric iron by oxygen in the air. The water combines to form a yellow contamination of the board surface.
The ferrous iron on the stone surface is oxidized to trivalent iron by oxygen in the air and combined with water to form hydrated ferric hydroxide, which has a very low solubility. Therefore, the yellowing pollution of the marble slab surface caused by iron is not easy to be removed. The second type of yellowing pollution of white marble slabs comes from the organic matter inside the marble, which is present in the formation of the marble, and its structure is similar to humus. These water-soluble organics present in the marble react with alkaline water and often show a brownish yellow color. Due to the existence of this organic matter inside the marble, when the marble floor or wall panel without waterproofing treatment on the back of the board is wet-pasted and installed, the alkaline water of the grout seeps through the marble and reacts with the organic matter in the marble to produce a colored product , When these colored products are brought to the stone surface by water, the second pollution of the stone surface is formed.
Even during the use period after the marble stone is installed, due to climate reasons, whenever water seeps through the cement concrete and then seeps out of the marble stone surface, it will always bring colored organic pollutants to the stone surface.
Influence of external reasons on white marble
The above two types of pollution of white marble come from the internal composition and structure of the stone, and occur under the influence of external conditions. In addition to these two types of pollution related to the composition and structure of the stone, the pollution from the outside also has the following aspects:
- The yellowing caused by wear and tear is caused by the wear of the marble polished surface, and the dirt is brought into the marble surface with walking. holes, which make the surface of the white marble appear yellow.
- Yellowing caused by incorrect care The most common incorrect care is to wet the ground with a dirty mop. The dirt brought by the dirty mop accumulates in the marble, making the white marble surface polluted and yellowed.
- Yellowing caused by waxing When the marble surface is polished with wax, the thick wax layer turns yellow due to its own aging.
- Yellowing caused by crystal surface treatment The steel wool used for crystal surface treatment remains in the micropores of the polished white marble slab with tiny fine powder, which becomes the source of yellowing, especially when the marble is in a wet state for crystal surface treatment, Yellowing is more likely to occur.
- The yellowing caused by the installation process The yellowing caused by the installation is easy to be ignored, but it is widespread. Before the white marble floor or wall is installed, although the so-called six-sided waterproofing treatment is performed on the stone specification board: the bottom surface is waterproof and adhesive, and the four sides and the front are treated with penetrating waterproofing agent. If such a six-sided waterproof treatment is done very well, the quality of the selected waterproof material is also guaranteed, and theoretically, water-related yellowing should not occur again. But the fact is that even the six-sided waterproofing of the marble stone slab before installation is considered to be well done, and the yellowing of the marble slab after installation still occurs from time to time.
- The yellowing phenomenon related to the installation is mainly caused by two aspects. One is that due to the installation size, the on-site cutting destroys the original waterproof treatment of a certain side; the other possible situation is that the construction environment is dirty and the construction process The medium cement slurry falls on theslabsurface. In order to prevent the dropped cement slurry from drying out on the board surface, wipe the dropped cement slurry with a wet towel. Some dark cracks, because even if the surface of the marble slab has been treated with permeable waterproofing, it is impossible for tiny water repellent molecules to form a protective film across the cracks to shield and protect the cracks.
Therefore, the coverage of the waterproofing agent at the crack is very limited. During installation, scraping off the side of the specification board with cement slurry back and forth with an ash knife will also destroy the waterproof treatment that has been done. If the cement water is accidentally brought into the cracks of the marble surface when wiping the board surface, the slab surface will turn yellow sooner or later, not whether it will turn yellow.
Prevention of yellowing of white marble
To prevent quality problems such as yellowing of white marble, the following points must be paid attention to in the process of processing and installation, so that white marble can perfectly present the beauty of decoration.
- Due to the internal composition of marble.
Structurally induced yellowing occurs through external conditions. This external condition is water and oxygen in the air. Therefore, as long as water is effectively prevented from passing through the interior of the stone, the yellowing caused by the composition and structure of the stone will be effectively suppressed.
- An effective way to prevent water from passing through the interior of the stone is to waterproof the back of the slabbefore the marble stone is installed.
Early marble stone slab back waterproofing treatments were brushed with siloxane/silane penetrating waterproofing agents. Facts show that coating the back of the board with this waterproofing agent cannot effectively inhibit the occurrence of stone lesions including yellowing. Penetrating water repellents have certain limits. No matter how good the waterproofing agent is, its waterproof performance will gradually decline due to the influence of the environment. This is why after the first application of the waterproofing agent, it is necessary to repaint it at regular intervals to repair the deterioration of its waterproof performance. For this reason, penetrating water repellents are only suitable for white marble surfaces that are ready to be repainted, such as the front of a floor or an outward-facing wall. When a penetrating water repellent is applied to the bottom of the board, the water repellent function of the water repellent cannot be monitored. Even if there are signs that the waterproofing agent has deteriorated, we cannot reapply and repair it, but can only let it deteriorate and lose the waterproofing function completely. This is the main reason why many projects still cannot avoid stone lesions by adopting this floor installation process. A kind of stone waterproof adhesive with cement as the base material and high molecular polymer emulsion came into being. This kind of waterproof adhesive is called two-component waterproof adhesive. One component is mainly cement, with other inorganic fillers and a small amount of polymer additives, and the other component is organic polymer emulsion. This two-component waterproof adhesive must be mixed on site, and workers who lack professional knowledge often do not realize the importance of the proportion of the two components, and do not mix in strict accordance with the specified proportion. Therefore, the quality cannot be fully guaranteed. In addition, there are many brands of this type of waterproof adhesive, and the quality is uneven. For example, the type of polymer in the emulsion is improperly selected or the solid content is too low, which may not be waterproof. This two-component waterproof adhesive is not suitable for white marble with high iron content or marble with more dark cracks, because when this waterproof adhesive is applied, strong alkaline cement water will immediately enter the cracks of the stone or capillary pores and seepage from the slab surface, yellowing of the marble surface may occur soon.
- For the yellowing of white marble caused by external reasons, it can be prevented through reasonable use and maintenance.
For example, a fiber carpet is placed at the entrance to remove the sole sand or other hard particles before entering the marble paving area, so as to reduce the wear of the marble stone slab by the foreign hard particles. The mop used to clean the floor should be kept clean, the water used for mopping the floor must be clean, and the water on the ground should be wiped clean after mopping the floor. If possible, it is best to use marble cleaning fluid for maintenance. Floor waxing has proven to be a method of marble deck maintenance that does more harm than good. First of all, the luster of the ground polished with wax does not last for a long time. On the other hand, most of the wax has a blocking effect on the ventilation capillaries of the stone, which hinders the normal gas passage of the marble that is adjusted with the climate. Finally, when the accumulated wax layer turns yellow due to aging and needs to be removed, a wax remover must be used. The use of wax remover will seriously affect the indoor air quality. Crystal surface treatment is a commonly used polishing treatment for marble floors. Choosing the correct crystal surface agent can make the treated stone surface obtain a dense, bright film that does not affect the breathability of the stone. However, when the crystal surface is processed, such as polishing with steel wool, the fine powder of steel wool must be cleaned with a vacuum cleaner. Any finely divided steel wool powder remaining on the ground may become a source of pollution for the yellowing of the marble slab surface.
- The practitioners of stone installation must have a certain professional foundation, understand the reasons for the yellowing of the white marble stone, have the necessary skills to install the stone, keep the construction environment clean and tidy, and avoid the yellowing of the stone caused by the installation.
Care for the stone scientifically and avoid the introduction of iron from the cleaning water or the floor polishing process that will make the white marble turn yellow. Use a good quality penetrating water repellant to regularly protect the floor to reduce the time and opportunity for water to come into contact with the marble stone.
Therefore, the effective prevention of yellowing of white marble should be a comprehensive measure. In the case that the cement floor or wall is not effectively waterproofed, the treatment of the back of the marble stone slab is particularly important. Selecting a quality-assured waterproof adhesive to waterproof the back of the board is the most important step in all measures.
Methods of dealing with yellowing of white marble
- Once the yellowing of the white marble slab is found, first find out the cause of the yellowing. Before turning the suspicion of the cause of yellowing to something to do with rust, make sure that the yellowing is not caused by aging wax or other external factors.
- After eliminating factors other than iron, white marbleneed start preparing for rust removal. At present, there are various brands of iron and yellow removers in stone care shops. Although no product discloses the basic chemical composition, most of the iron and yellow removers on the market are acidic. Due to the poor acid resistance of marble, many acidic rust removers also have great erosion on the slabsurface while removing rust. Excessive erosion of the marble slab will cause permanent damage to the slab. Therefore, when using a rust remover, remember to stick several layers of toilet paper on the surface of the stone when removing yellowing, and then pour the rust remover on the paper. Wait for about two hours, the yellow will gradually decrease, and the yellow can be removed after a few times. Professional stone care personnel generally use weakly acidic or even neutral cleaning agents to minimize damage to the marble stone.
- For the stubborn rust spots, use the paste method, that is, mix the rust remover and diatomaceous earth with water to make a paste, then apply the paste on the rust spots, cover with plastic film and use self-adhesive tape around it. Seal it, remove the dried paste after 24 hours, and collect the dissolved iron with a special cleaning agent after the removal is completed.
- The last step is very important for marble, granite, sandstone and slate tiles to remove stains, yellow and dirt, because in the process of removing rust, when iron ions diffuse to the board surface, if the iron ions diffused on the board surface are not collected cleanly , the secondary yellowing will occur soon, and the area will be wider. Of course, you can also remove yellowing at home by yourself (as shown in the picture below)
In view of the fact that rust removal on white marble slabs is a professional work, it is not recommended that non-professional owners or non-professional caregivers purchase unfamiliar rust removers to remove the macular or rust spots of the marble stone, so as to avoid improper use of the marble stone permanent damage.