According to the chemical structure and form of its active ingredients, silicone waterproofing agents are mainly divided into four types: methylsiliconol salts, silicone resins, silanes and silicone emulsions. Each type has its own unique chemical composition, reaction mechanism and performance characteristics, suitable for different application scenarios and substrate requirements. In-depth understanding of these classifications and their characteristics is the basis for scientific selection and correct use of silicone waterproofing agents.


Methylsiliconol salts are the first generation of silicone waterproofing agents, and its representative products include sodium methyl silicate and potassium methyl silicate. In industrial production, methylsilanol is usually obtained by hydrolysis of methyltrichlorosilane, and then reacted with sodium (potassium) hydroxide solution at 90-95°C. This type of waterproofing agent is a rigid waterproof material. When used, it can react chemically with the surface of the substrate and carbon dioxide and water in the air to form a polymethylsiloxane hydrophobic film with a mesh structure. This film can effectively block the capillaries inside the cement mortar and enhance the density and impermeability of the material. Methylsiliconate has the advantages of low price, simple construction, and can be constructed on wet base surfaces. It has no corrosion effect on steel bars and has micro-expansion characteristics that can compensate for the shrinkage of mortar and concrete. However, this type of product also has obvious disadvantages: strong alkalinity (pH value can reach 13-14) not only has the risk of corrosion to the skin of construction workers, but also may cause white powdery precipitation or yellowing on the surface of the substrate, affecting the appearance; in a strong alkaline environment, the generated silanol will dissolve in water and flow away, causing the waterproof function to gradually fail.


The active component of silicone resin waterproofing agent is mainly methyl silicone resin, which is usually produced industrially by hydrolysis and polycondensation of methyltrichlorosilane in organic solvents, or by the reaction of methyltrialkoxysilane under the catalysis of excess water and trace hydrochloric acid. Silicone resin has excellent high and low temperature resistance (-60℃ to 250℃), outstanding aging resistance and unique hydrophobic-breathable balance, and is considered to be one of the most ideal waterproof coatings. Studies have shown that the ratio of n(CH3)/n(Si) in methyl silicone resin has a significant effect on its performance. When the ratio reaches 1.4, the resin exhibits the best waterproof and alkali resistance, and is expected to achieve a more lasting protective function. However, silicone resin waterproofing layers also have problems such as high gloss and poor scrub resistance, which affect the consistency of the building's appearance; more importantly, unmodified silicone resin waterproofing layers can usually only maintain their effects for a few months to 2 years, and then gradually fail. Increasing the methyl content and molecular weight of silicone resins, or through composite modification, is the main technical approach to extend its service life.


Silane waterproofing agents, especially long-chain alkyl alkoxy silanes (n≥8), represent the most advanced silicone waterproofing technology. This type of product has the characteristics of small molecular weight, strong penetration (penetration depth can reach 6-12mm at a concentration of 100%), and moderate reactivity. When used, it only requires no water, dust or oil on the surface of the substrate for construction. It is easy to operate and safe and environmentally friendly. Silane waterproofing agents can react with hydroxyl groups inside the substrate to form a chemically bonded three-dimensional network structure, which not only provides excellent waterproofing performance, but also has comprehensive protection functions such as UV resistance, oxidation resistance, antifouling and wear resistance. Wacker's SILRES® BS 1701 (the main component is octyltriethoxysilane) and Dow Corning's Z-6689 (silane/siloxane mixture) are typical representatives of this type of product, which are particularly suitable for the treatment of alkaline or neutral substrates such as concrete and stone. The biggest advantage of silane waterproofing agents is their durability. Application cases in European and American countries show that their waterproofing effect can last for 10-20 years. However, this type of product has high technical requirements, limited domestic production capacity, and relatively expensive prices. At present, it mainly relies on imports.


Organic silicone emulsion waterproofing agents are dispersion systems of linear polyorganosiloxane in water, mainly including methyl hydrogen silicone oil emulsions, hydroxy silicone oil emulsions and alkyl alkoxy silane emulsions. Compared with the previous categories of products, silicone emulsions have the advantages of being environmentally friendly (no solvent volatilization), strong penetration, and low cost. Among them, methyl hydrogen silicone oil emulsions contain highly active Si-H bonds, which are easy to react with the hydroxyl groups on the surface of the substrate to form a mesh waterproof film; while alkyl alkoxy silane emulsions combine the high efficiency of silanes with the ease of use of emulsions, becoming a popular product on the market. Dow Corning's DC-772 and Momentive's SC-50 are typical representatives of this type of product, which are widely used in the treatment of various substrates such as bricks, stones, and concrete. In recent years, the cream-like silane products developed by Wacker have further enriched the form of silicone emulsions. This high-solid content, low-volatile product is particularly suitable for top and vertical surface construction, and can significantly reduce material loss. The main challenge of silicone emulsions is stability control. Demulsification or stratification is prone to occur during storage and transportation, affecting the use effect.


Table: Performance comparison of four major types of silicone waterproofing agents


Methylsiliconate Sodium (potassium) methyl silicate Low price, easy construction, usable on wet surfaces Strong alkalinity, whitening on the surface, poor durability


Silicone resin Methyl silicone resin High and low temperature resistance, aging resistance, good air permeability High gloss, not resistant to scrubbing, easy to fail


Silanes Long-chain alkyl alkoxy silane Deep penetration, strong durability, environmentally friendly and safe High price, high technical requirements


Silicon emulsion Silicone oil or silane emulsion Environmentally friendly, good penetration, moderate cost Poor stability, high storage requirements
In practical applications, compounding technology has become an important way to improve the performance of silicone waterproofing agents. By scientifically matching different types of silicone compounds or other materials (such as fluorine compounds, acrylates, etc.), we can complement each other and obtain a more comprehensive protective effect17. However, no matter which product, it is not a "universal" solution. It must be selected according to the characteristics of the substrate, environmental conditions and usage requirements to achieve the best waterproofing effect and economy.