(A) the causes of water spots or water marks
As a stubborn disease of architectural decorative stone, water stains or water marks mainly refer to wet marks or punctate marks similar to wet marks on the surface of decorative stone, whose main feature is that these wet marks are always dry; Or is not easy to completely dry; Or people always feel that there are traces of water wetting, even if the sun shines or is baked with fire, then the wet traces will still remain. The causes of water spots or water marks on stone materials are related to the nature of stone materials, surrounding environment and installation and construction methods. Stone has many micropores, that is, it belongs to microporous materials, most of which are one. Stone is also hydrophilic, which can automatically absorb water and transfer moisture. From the analysis of formation mechanism, there are mainly four kinds of water spots or water marks on the surface of decorative stone:
First, stones are directly or indirectly related to moisture or water. For example, some adjacent wet floors and walls in the south, or places where water often seeps out nearby, can often see wet marks on the stone surface near the stone cracks.
The second reason is that there is some salt or alkali in the micropores inside or on the surface of the stone. These salts or alkalis are often concentrated on the surface of stone with the evaporation and continuous replenishment of water on the surface of stone after pasting. There are two kinds of water spots formed in saline-alkali land. One kind is some deliquescent salts or alkalis, whose water vapor pressure is very low, so they will absorb water until they are in equilibrium with the external water vapor pressure. The additional pressure (micropore capillary phenomenon) produced by the micropores of stone makes the balance more conducive to absorbing more water, so no matter what the external weather is, the water on the surface of stone will never dry. The other is the translucent crystals of some salts, which occupy the micropores of the stone and change the reflectivity of the surface light, so that the stone looks wet.
The sources of salt and alkali on the stone surface mainly include: ① the salt and alkali components of cement, putty paste or additives during wet bonding; (2) Soluble saline-alkali in nearby soil or groundwater that migrates with water; (3) sediments after environmental pollution or acid rain; (4) Salt brought in by stone during mining, processing, handling and open storage, such as cooling liquid for sawing and polishing; (5) stone into the cleaning solution and nursing solution after installation. The third is the water spots formed by the mineral reasons of the stone itself. In addition to some soluble salts and unstable chemicals contained in stones, some stones also contain inclusions, which are foreign substances "captured" in the process of rock formation, and they may exist in gaseous, liquid or solid forms. When the rock is cut, some of them will gradually spread to form spots, while some spots only make the local color slightly darker, much like water wet marks.
The fourth is a dry mark similar to water spots. The reason is that wet sticking, water seepage, moisture under the decorative surface, or the immersion of other wet sticky bodies make a certain area of the decorative surface of stone in a wet state for a long time. Wet surface absorbs dust more easily than dry surface, and the adsorbed dirt will penetrate into the micropores on the stone surface after a period of time. Even if the whole decorative surface is dried later, the mark of water spots displayed by dirt will remain.
Among the above four kinds of water spots (or water marks), the second one is the existence of soluble saline-alkali which is the most harmful to stone. Salt crystallization damage (also known as salt weathering) has always been considered as the most important threat to the destruction of stone buildings and stone cultural relics.
(2) Methods of removing water stains or water marks
For the above water spots (or water marks) with different causes, the removal methods are different: the first one needs to remove water or cut off the water source; The second one needs to remove salt or alkali from micropores; The third and fourth need to remove colored substances or dark substances. Among the four kinds of water spots (or water marks), the second and fourth are the most common. This paper also mainly discusses the removal methods of these two water stains (or watermarks).
At present, there is little research on the method of removing water stains (or water marks) abroad, and the following points can be found:
(1) Slim-Surrey mentioned a method to remove water marks and mineral deposits on hard surfaces in the U.S. patent, which mainly uses viscous fluids of inorganic acids, lubricants and thickeners to clean hard surfaces. Inorganic acids are used to remove spots, such as calcium salts and precipitated metal oxides, and the better concentration is 3 1%-37% wt. Choosing glycerin or mineral oil as lubricant can improve the dispersibility of the components, and its preferred concentration is 15% ~ 30wt. The thickener can be gelatin or silicon dioxide, or their mixture, and its concentration range is 3-65 %+ 06% of the total weight of the composition. In order to achieve the effect of fluidity and certain viscosity, the viscosity of the final composition should be 1.73-76000 centipoise. In addition, a dispersant or an anti-flocculant, such as a surfactant using octadecane suspension, may be added. When colloidal silica is used, the particle size and its influence on viscosity should be considered, and the particle size is preferably 0.3-0.5 micron. If the solution is unstable, a mixture of one or more dispersants or antiflocculants can be used, and the amount of dispersants or antiflocculants is about 40% or less of the total weight. Other related ingredients can also be added, including dyes, fragrances, solvents or enzymes. Adding these solvents or enzymes is beneficial to the dissolution of dirt mixture. It is said that the invention can efficiently, conveniently and quickly clean dirt on porous and non-porous hard surfaces. When the composition is at a high viscosity, such as 76,000 centipoise, the detergent becomes gel. This is very convenient for cleaning vertical, inclined or inverted hard surfaces.
(2) Peter Charelli introduced a bleaching cleaning agent to remove water stains in another American patent. It is said that it can remove dirt from walls and ceilings, and only need to spray or rub cleaning agent on the stained surface, without wiping the surface too much. This detergent is made into powder and mixed with water to form an aqueous solution containing 3-8 wt% solute. The formula of the powder is: bleaching agent 60-80wt%, surfactant 0. 1- 10wt%, water-soluble anionic polymer 0.1-0/0wt%, and other inert components 5-40wt%.
(3) Hideyoshi Yanong introduced a cleaning agent for cleaning stains on hard surfaces such as concrete, stone and brick in Japanese patent. This is an aqueous cleaning agent, which consists of mixed acid 5-25wt% (water spots are also mentioned), fatty acid 003- 1wt%, alkyl ether 0.2-5wt% and ammonium chloride 5-40wt%.
(4) Hairong-Made et al. introduced a foam cleaning agent in Japanese patent, which was used to clean the scale dirt on hard surfaces, especially the inorganic dirt in bathrooms and bathrooms and the synthetic dirt in kitchens. It is said that it has long-term protection ability after cleaning, and the formula includes 0. 1 ~ 30wt% serine or its salt and 0. 1 ~ 50wt% water-soluble solvent.
(5) Wu et al. introduced a cleaning agent in Japanese patent, which is said to clean the water stains on the surface of ceramic products. Its formula is relatively simple, and it is mainly a mixed solvent of chloromethane, isopropanol and other components. The weight ratio of chloromethane to isopropanol is 90-65. We have carried out experimental verification on some formulas that can be found and some products imported from abroad. The results show that some formulas and products are completely ineffective, while others are slightly effective.
In order to develop a new stone water stain remover, we have carried out a variety of theoretical and experimental studies in combination with the graduation thesis work of undergraduates. At present, a compound stone water remover (ZDF25) has been developed. It is an aqueous solution that meets the requirements of environmental protection and has been used in some cleaning projects at present. It has a good cleaning effect on saline-alkali water stains or water marks, which is the second kind of water stains mentioned above.
(3) to prevent water spots or water marks
As mentioned above, water stains are harmful and difficult to remove. With the deepening of people's understanding of the causes of water stains, the prevention of water stains or water marks has gradually become the most concerned issue for owners, designers and construction units of stone decoration projects. According to the four causes of water damage, the commonly used preventive measures before construction mainly include the following:
(1) Because stone is a hydrophilic microporous material, it will automatically absorb and transfer water. Attention should be paid to blocking water source, isolating moisture and draining water in time, which are the primary problems that must be inspected in stone decoration engineering;
(2) Fill the capillary holes at the bottom of the stone to protect the bottom of the stone, so as to prevent the saline-alkali components in cement, mortar or cushion additives and the soluble saline-alkali in the nearby soil or groundwater from infiltrating into the stone. The components of stone bottom protective agent are mainly organic polymer resin or inorganic colloid, mostly film-forming substances;
(3) Carry out surface protection (waterproof) treatment on the front and side of the stone to avoid bringing salt water or dirt to people due to construction, environmental pollution, cleaning and nursing. The most commonly used surface protectants are silicon or fluorine (organic or inorganic) compounds, which have certain permeability and hydrophobicity, and most of them have no obvious film layer and have certain permeability; (4) Choose stone with stable chemical composition to avoid spots caused by changes in the mineral composition of stone.
In a word, water spots or water marks on stone are difficult to cure lithiasis, and it is the most economical and effective method to take preventive measures in advance. If there are water spots or traces, we also have chemical removal methods at present, and the most important thing is to prescribe the right medicine.