Let's first understand which stones are prone to hollowing when Marble Sculptings are made.
1. Stone
①Water absorption: The lower the water absorption, the higher the structural density and the better the physical and chemical properties. However, the adhesion between natural stone products with low water absorption rate and paving cement is weaker than that of products with high water absorption rate, and the reason why stone products with a water absorption rate of less than 0.5% are easier to hollow and fall off. Therefore, special treatment such as back glue and back sand should be done.
②Hygroscopic expansion: Stone products with high water absorption rate are paved in a humid environment, and after long-term absorption of moisture, they gradually expand themselves and cause separation and shedding from the cement. This phenomenon mainly occurs in stone products with excessive hygroscopic expansion rate. Therefore, special surface treatment such as protection and coating is required.
③Natural stone back net: Some natural stone will have a back net after processing and leaving the factory, which should be cleaned. Make the natural surface of the natural stone in direct contact with the paving cement adhesive to increase the bond firmness with the cement and prevent hollowing or falling off.
2. Adhesive material
①Unqualified cement has insufficient bonding strength, poor volume stability, and excessive expansion rate in the later stage, which will lead to hollowing of natural stone.
If you choose early-strength cement when laying natural stone, the cement will lose its fluidity prematurely, so that the cement mortar layer cannot be completely combined with the natural stone, resulting in hollowing and falling off after a period of time.
Some cements have poor bleeding properties. After the natural stone is paved, a layer of water film will appear between the natural stone and the cement layer, resulting in poor bonding of the natural stone.
When choosing cement, you should choose ordinary cement produced by large companies as much as possible, and it is best not to choose early-strength cement. In addition, the higher the cement grade, the better, and 32.5 grade cement can meet the requirements for natural stone paving.
② The proportion of cement mortar does not meet the requirements, or the proportion of water in cement mortar is too high, which will lead to excessive water loss after drying, resulting in hollowing.
Then some wrong operations in Marble Sculpting construction will also cause hollowing, and a conclusion has been drawn based on years of experience.
①Foundation of the wall and floor: The residual wallpaper, adhesive, and floating ash on the untreated wall and floor will cause poor bonding on the bonding surface, resulting in hollowing.
②Cleaning of the bonding surface: Natural stone may have dust, slurry or other stains on the back during production, transportation and storage. It should be cleaned with a clean brown brush and dried before paving. If necessary, add 108 glue with 3%~5% of cement weight into the cement mortar, so that the bonded mortar has better compatibility and water retention, and has a certain retarding effect, which not only increases the cohesive force, but also reduces Adhesive layer thickness, ease of veneering quality.
③Reserved expansion joints: The linear expansion coefficient of natural stone is 3 to 7×10-6, which is about half of that of concrete. Reserve 2-5mm expansion joints for paving as required, which can disperse the volume expansion stress of the combination of different expansion coefficients caused by the temperature difference between cold and heat. Although the "dense seam paving" method without leaving gray seams has the advantages of being beautiful and easy to clean, large changes in ambient temperature, especially when it is suddenly cold, will easily cause natural stones to arch and fall off, especially large-scale natural stones.
④ Exhaust when natural stone is bonded: For large-scale natural stone, if the thickness of the bottom mortar is uneven when laying and pasting, basin-shaped depressions appear, and the exhaust is not sufficient when tapping during bonding, and hollowing may appear on the contact surface Phenomenon.
⑤Climate changes during construction: the climate is dry and cold in autumn and winter, and water is easy to lose, which may cause hollowing if you do not pay attention. If the temperature difference between day and night is too large during construction, due to the different expansion coefficients, it is easy to cause hollowing and falling off during the bonding stability period.
⑥ During the stable period of natural stone paving, trampling or other uneven loads will affect the firmness of the bond, resulting in the occurrence of hollowing and falling off, which should be avoided.
⑦Due to the above factors, it is not suitable to paste large-scale natural stone on the wall directly with cement. There are dry-hanging, back-bolt, and strong glue methods for wall paving.
