How to deal with the phenomenon of stone “returning slurry”?

With the development of the construction industry and the progress of construction technology, in the field of granite, a variety of new materials and new techniques are constantly used in various types of exterior wall decoration. The natural granite itself has the characteristics of good texture, solemn appearance, and excellent physical performance, which can also be carried forward and become more known. However, in some projects, after the completion of the granite finishing project for a period of time, some projects will have quality problems such as “slurry returning”, which will seriously affect the final effect of the entire decoration project. So, what is reflow ‘and how does it occur? How should we prevent the occurrence of such phenomena?

01. How does “backflow” occur?

The so-called backflow is generally due to issues with the installation quality of building materials, resulting in excessive moisture inside the building. Over time, the surface of the decoration may have inconsistent colors such as white flow marks, white spots, water spots, and moisture marks. The occurrence of this situation is generally related to the long-term contact of the cement used with moisture, which leads to the precipitation of calcium carbonate. On the one hand, the use of cement mortar wet hanging method is relatively common in the installation process of decorative building materials. During and after the installation of building materials, water from the outside continuously wets the gypsum and alkali salt components in the cement, causing the liquid containing various impurities inside the decorative building materials to gradually seep out and hang on the surface of the stone, forming the so-called backflow;

On the one hand, in the installation process of some building finishes, especially the facade exterior stickers, the workers mix the cement too thinly, causing a large amount of water to gradually evaporate after installation, resulting in hollowing out inside, which allows a large amount of moisture from the outside to enter the interior and continuously react with the cement, forming a slurry return;

On the one hand, some workers do not pay attention to sticking the building materials tightly when installing them, which can also lead to internal hollowing and the formation of backflow; On the one hand, some workers may neglect to point and waterproof the joints of decorative building materials during the operation process. Building materials that have not undergone waterproof treatment are prone to removing gypsum from the interior of the building materials after encountering external water vapor such as rainwater, which can lead to mortar return on the walls of the building materials. This situation is common in some southern regions;

On the other hand, although some workers pay attention to waterproof treatment for the joints, they choose some acidic silicone sealant, structural adhesive, and marble adhesive during the operation process. After installation, the building materials and cement gradually corrode, and under the action and driving force of water, it slowly forms a backflow on the surface of the stone.

In addition to the above factors, failure to clean the building materials and veneers during the processing of building materials can lead to some contamination of the building materials and veneers themselves. After veneering, it is easy to cause the bonding between the building materials and cement mortar to be not tight, leading to the occurrence of hollowing. Once water deepens, it causes calcium carbonate to precipitate and form a backflow.

02. How to prevent the occurrence of slurry returns?

The occurrence of the backflow phenomenon will seriously affect the final effect of the entire decoration project. Therefore, in the actual operation process of stone materials, we should start with various details that are prone to water vapor invasion, and do a good job in the installation of various details to ensure that the building materials are closely combined with cement mortar, in order to prevent the occurrence of slurry return.

On the one hand, operators should carefully clean the stone materials. In practical operations, stone products often go through a very long process of mining, processing, and repeated transportation before delivery, making them easily contaminated by dirt such as oil stains and dust. During the installation process, the dirt remaining in the stone products will inevitably affect the bonding between building materials and cement mortar, leading to the occurrence of hollowing. Therefore, it is necessary to carefully clean the stone before installation. Similarly, we should also do a good job of cleaning the building veneers in order to avoid such incidents.

On the one hand, operators should strictly follow the standard requirements for installation operations, especially mastering the water-cement ratio of cement mortar. If the mixture is too thin, it is easy to cause hollowing of the stone due to water vapor evaporation during subsequent use. At the same time, operators should try to apply the compaction force evenly to the surface of the stone when paving, and try to ensure that the bonding thickness between the stone and cement mortar is as uniform as possible. It should also be noted that during the operation process, especially in the decoration process of outdoor building finishes, special attention should be paid to waterproofing work. After the surface layer of the finish is completely dry, relevant operations can be carried out, which can greatly eliminate the quality hazards of the external pasting.

On the other hand, operators should not only use special stone caulking agents at the joints during installation to reduce the occurrence of bending and protrusions on the stone surface but also clean the stone gaps. They can use a steel saw to cut about 2mm into the stone joints to remove residual ash between the gaps, and then use glass glue or shoes of the same color to grease the gaps tightly to prevent rainwater or moisture from soaking in the gaps.

In case of grout return, if it is at the window edge, wall top, parapet, and other locations, we need to redo the back waterproof layer of these problems. If it is due to the phenomenon of hollowing that leads to grout return, we need to analyze it in detail and use methods such as grouting treatment, negative pressure treatment, or pressure treatment to deal with the phenomenon of hollowing. If not, the phenomenon of slurry return is likely to occur repeatedly.

For stone finishes contaminated by backflow, we can carefully remove the remaining thin layer of calcium carbonate on the finish with a scraper, clean it carefully with oxalic acid or a special cleaning agent, and then wipe the joints with glass glue to achieve the goal of eliminating backflow. But before use, it is necessary to make a small sample test block to verify the effectiveness of the cleaning agent and decide whether to use it. Moreover, it is worth mentioning that due to the fact that soluble alkali or salt substances have already penetrated into the stone along the pores, it is difficult to remove them. Therefore, for the phenomenon of slurry return, prevention should still be emphasized.

Of course, we can also reduce the incidence of slurry return accidents by selecting low-alkali cement, alkali-free cement, or using high-density stone products as decorative stones. Anyway, it is always the most important to firmly control quality in actual construction. In this way, not only can it improve the service life of stone veneer engineering, but it can also avoid adverse effects on the company’s reputation caused by rework, repair, etc.

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