First, white is the cause of all problems.
Before all the analysis, it must be pointed out that the problem of yellowing is by no means the patent of Baishi. The substance and action process leading to yellowing run through the whole process of stone mining, processing, paving and maintenance. In other words, these problems should actually exist in all stone materials.
Just because of the contrast of white, as long as it is slightly yellow, it is visually obvious and difficult for consumers to accept. On other colors of stone, slight yellowing is not obvious, and the problem is not as prominent as white stone.
In life, white clothes are the least resistant to dirt, which is also the reason.
Second, what substance will cause the white stone to turn yellow?
Yellowing of white stone is caused by the following substances:
1, iron
Iron is one of the main substances that cause stones to turn yellow. Both the iron in the stone itself and the foreign iron are oxidized into ferric oxide (Fe2O3), which leads to the rust yellow of the stone.
(1) Stone itself contains iron.
Although the iron content of white stone is not high, the rust yellow produced by these subtle contents is also obvious enough. As shown in the following figure, the fracture of the plate is rust yellow formed by its own iron.
② Exogenous iron
In the whole process of mining, processing, transportation, installation and maintenance, stone materials will come into contact with all kinds of foreign iron and have the opportunity to produce rust yellow. Such as: mechanical corrosion during mining and processing, corrosion of various iron frames during transportation, various steels during stacking, various steel frames during installation, and steel wool scraps during crystallization and polishing.
(3) How did iron become rusty yellow?
However, just seeing iron is not enough to explain many problems. Teacher Lei's article brilliantly expounds the mechanism of iron forming rust yellow in stone. In this paper, Mr. Lei reached a scientific conclusion through a series of rigorous experiments. We summarize as follows:
*? Test 1: Baishi is not easy to rust and turn yellow when contacted with deionized water.
*? Experiment 2: Baishi, exposed to alkaline water, has a serious rust yellow.
*? Conclusion 1: oxidation and hydration are indispensable in the yellowing process of rust.
*? Conclusion 2: Alkaline water can easily lead to the yellowing of white stone, because in alkaline solution, the redox potential of ferrous iron oxidized to trivalent iron is reduced, and it is easy to be oxidized to trivalent iron by oxygen in the air. That is, iron oxide, the component of rust.
④ Alkaline substances around us.
Iron+oxygen+alkaline solution = accelerated rust yellow. This conclusion can explain many phenomena.
*? Don't choose the wrong protective agent
For example, as mentioned earlier, this common yellowing phenomenon did not exist in the Baishi project we contacted many years ago. Why?
10 years ago, the concept of stone care was not as popular as it is now. At that time, stone was rarely protected, and white stone was not used.
But now, why is there such a common yellowing phenomenon in Baishi? The problem only appears in stone protection.
To be precise, it should be "methyl silicate", a protective material, which has caused today's large-scale problems.
It turns out that the stone care industry has long given professional stone protectants. However, in practical engineering, many people only use the cement waterproof agent "methyl silicate" as a stone protective agent.
Methyl silicate, it's just alkaline!
Look at the experiment we did. We bought a barrel of methyl silicate waterproofing agent at random from the market and tested it with PH paper. What was the result?
Strong alkalinity!
You don't need a professional protective agent, but it's cheap, so how much money can you save? Once the rust turns yellow, it is difficult to clean it!
Therefore, for Baishi, it is forbidden to use this unprofessional protective agent, and it is best to use high-quality osmotic protective agent.
*? Cement wet slurry
In addition, the white stone is wet pasted with cement, if the back is not well protected. Cement is also an alkaline substance, which can also cause the white stone to turn yellow.
Cement is also alkaline.
2, organic matter, pigment pollution
(1) Organic matter in the stone.
Continue to quote Mr. Lei's achievements, "There is organic matter in the stone. If the back protection is not done well, when the cement wet slurry is used, the alkaline aqueous solution will react with the organic matter in the stone to generate a brownish-yellow substance, which will seep out of the stone surface, thus forming a yellowing phenomenon. "
② Exogenous pollutants
If the white stone is not well protected, or the role of protective agent is reduced or disappeared for various reasons, all kinds of pigments and pollutants from the outside will stay in the micropores of the stone, which will change unpredictably and turn yellow over time.
In addition, some links in stone processing will use wood. The pigment in wood penetrates into stone, which will also cause yellowing. In addition, some grinding discs will fade when polished, which will cause yellowing and other pollution to the white stone.
external factor
3, glue oil, oil.
Colloidal oil pollution is also an important factor causing stone yellowing.
(1) marble glue, glass glue, dry hanging glue are used on stone materials. If the quality is poor or used improperly, the glue oil will seep out. The color of the polluted stone will generally appear brown, yellow and so on.
(2) Inferior epoxy resin adhesive will also decompose amino acid components when used, and react with oxygen in the air to generate yellowish substances. When used on stones, it will also cause yellowing.
(3) The protective agent with poor permeability, which contains impurities in the solvent, will also cause yellowing when used in white stone. Therefore, Baishi must choose high-quality osmotic protective agent.
(4) Oil such as engine oil, kerosene and diesel oil. When the amount is small, it is generally brown. In addition, organic substances such as animal and vegetable oils are yellow after oxidation, which is more common in restaurants.
⑤ Improper use of dust pushing oil can also cause pollution such as yellowing of white stone.
Dry hanging glue pollution
Epoxy resin glue pollution
4. Other reasons
Other less common reasons, put white stone, the yellowing effect will be more obvious.
If the previous waxing technology is applied to white stone, the yellowing phenomenon is also very serious. Other reasons, I also expect you to continue to discover and supplement.
Third, how to prevent it?
As can be seen from the previous introduction, the white color is so delicate that there are many reasons for the yellowing of the white stone. And once something goes wrong, to be honest, with the current stone conservation technology, no one can guarantee that the stone can be restored to its original appearance.
Therefore, when we have mastered the knowledge introduced above, the best way to solve this problem is to pay attention everywhere and minimize these factors mentioned above.
1, mining, processing and transportation links
(1) Pay attention to avoid the influence of rust on machines and tools on Baishi in all aspects of mining and processing. If there is rust, try to remove it.
(2) to prevent the use of wood in all aspects, the pigment pollution of stone. For example, these Woods can also be painted with permeability protective agents.
(3) When doing protection in the factory, we should abandon the practice of only caring about the cost in the past, prohibit the use of unprofessional protective agents and inferior protective agents, and choose high-quality osmotic protective agents.
Step 2 install the link
(1) Before installation, be sure to protect the six-sided stone. And the protection of the back, it is best to use professional-grade stone glue for sealing.
② If possible, use adhesive instead of cement wet paste.
(3) The stone that was originally well protected will lose its protective function once it is re-cut according to the actual situation. Therefore, as long as there is cutting, brush protection.
(4) When installing, try to avoid cement sprinkling on the stone surface. Because even if the protection is done well, the stone has micro-cracks, and the alkaline components of cement penetrate into the stone along the micro-cracks, which will still cause yellowing.
⑤ When using various adhesives, choose high-quality products and operate according to the specifications.
Attention should also be paid to the installation process.
3, transformation and maintenance links
(1) It is forbidden to use steel wool and easy-to-fade polishing for renovation and maintenance of white stone. Bai Jie pad should be selected. However, the best way is to directly polish the white stone to a gloss of about 90 degrees with "VD easy-to-grind sheet", and then make a protective layer of silicon dioxide on it with glaze sealing technology.
(2) The white stone on the ground, trampled by people will wear the surface and reduce the protective effect. Dust removal mats can usually be placed at entrances and exits. It can absorb gravel and pollutants on the soles of feet to a great extent. Play a preventive role.
③ Daily maintenance, or recommended glaze sealing process. The main component of sealing glaze is silicon dioxide. On the one hand, the hardness is high; On the other hand, SiO2 _ 2 can also fill the micropores of stone, reducing the possibility of foreign pollutants entering the stone. It is most suitable for the maintenance of Baishi.
Pay attention to the above details. Baishi can be beautiful. No problem.
Four, white stone yellowing cleaning
As mentioned above, it is recommended to prevent the yellowing of white stone. Because if yellowing has occurred, it is very difficult to clean, and it is really difficult to ensure complete removal.
But according to the previous introduction. We can judge the different reasons first, and then take targeted measures.
1, remove rust and turn yellow
Yellow rust in a small area can be treated with "VD marble rust remover +VD stone pigment scavenger".
Step 1: Spray "VD marble rust remover" and "VD stone pigment scavenger" on the polluted surface. There are many rust removers and few pigment scavengers.
Step 2: Apply it with clean cotton yarn and paper towel, and then cover it with plastic film.
Step 3: remove the covering for more than 4 hours.
Step 4: Wash with plenty of clean water, and then drain with high power.
Step 5: Repeat the above steps according to the removal effect. Until the yellowing is removed.
Step 6: After the stone is dried, it is strictly protected with VD osmotic protective agent. Construction standard: sufficient, uniform and maintained for more than 24 hours.
Note that if it is a large area of rust yellow, it can be directly polished to remove it. Then use VD osmotic protective agent for strict protection.
2, organic matter, pigment pollution
According to the above steps, use "VD stone pigment scavenger" for cleaning, and use "VD penetrating stone protective agent" for strict protection.
3, glue oil, oil.
According to the above steps, VD stone degreasing and degumming agent, VD stone pigment scavenger and VD stone osmotic protective agent are used for treatment.
Note: For the application of small area cleaning, please refer to the following figure:
Small area application method
Enlightenment from verb (abbreviation of verb)
We can also see that preventing white stone from yellowing involves so many links and a wide range of knowledge. And once something goes wrong, cleaning technology is so complicated and time-consuming.
What does this give us?
That is to say, in the whole stone industry, there is still a lack of communication and cooperation between all links involved in the whole process of stone application, such as mining, design, processing, installation and maintenance. If we can communicate and coordinate well, many stone problems can be solved from the source.
At this point, we also expect the whole stone industry to move forward together.