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I. Definition of coatings Coatings refer to a general term for liquid or solid materials that are applied to the surface of objects to form a solid film with protective, decorative, or special functions such as insulation, corrosion prevention, or marking. II. Development of Coatings The earliest coatings used by humans were made from a combination of plant oils (such as tung oil), raw lacquer, natural asphalt, and natural pigments; they were solvent-free and pollution-free. With the development of human production, coatings based solely on natural materials could no longer meet the demands, leading to the emergence of synthetic coatings based on artificially synthesized resins, which satisfied the various needs arising from the advancement of high-tech industries such as modern industry. However, most synthetic coatings contain large amounts of organic solvents, as well as pigments, fillers, and molecular additives that are somewhat toxic, causing environmental pollution during production and use and affecting human health. III. Classification of coatings 1. By application: architectural coatings, marine coatings, electrical insulation coatings, automotive coatings, etc. Building coatings are further divided into those for indoor use, outdoor use, wood, metal, and concrete, among others. 2. By application method: painting, spraying, baking, electrophoretic coating, fluidized bed coating paint, etc. 3. Based on the function of the coating: primer, rust-proof paint, anti-corrosion paint, fire-resistant paint, high-temperature resistant paint, topcoat, secondary coat, etc. 4. By the appearance of the paint film: gloss paint, matte paint, semi-gloss paint, wrinkled paint, beaded paint, etc. IV. Composition of Coatings Coatings are typically composed of film-forming substances, pigments, solvents, and various additives. 1. Film-forming substances are the basis of coatings, serving functions such as forming a film; they mainly include various oils and resins, which can be natural substances like animal and plant oils, or synthetically produced ones such as phenol-formaldehyde resin and urea-formaldehyde resin. 2. Pigments are used to determine the color of the paint film and to enhance its resistance to ultraviolet rays and aging. 3. Solvents such as xylene, turpentine, propylene, and ethanol are added to the paint in order to reduce its viscosity and facilitate application. 4. To increase the flexibility of the coating, plasticizers can be added, as well as small amounts of chemical additives such as curing agents, matting agents, and preservatives. V. Functions of coatings Generally speaking, coatings have decorative functions, protective functions, and functions to improve living conditions. 1. The decorative function involves altering the original appearance of a building by beautifying it, making it colorful and visually attractive. 2. Protective functions refer to the capabilities that enable buildings to resist the effects and damages caused by external climate conditions, such as anti-aging, mold prevention, fire resistance, heat retention, and thermal insulation – all of which are special protective functions. 3. Improving living functions refers to the function of enhancing living conditions through interior painting, such as sound insulation, sound absorption, and damp resistance. VI. Main functions and characteristics of exterior wall coatings The main function of exterior wall coatings is to decorate and protect the exterior surfaces of buildings, giving them an attractive and neat appearance and thereby helping to beautify the urban environment. At the same time, exterior wall coatings can also protect the building’s exterior walls and extend their service life. To achieve optimal decorative and protective effects, exterior wall coatings should possess the following characteristics: 1. Good decorative quality: The coatings need to have a rich range of colors and excellent color retention, enabling them to maintain their original decorative properties for an extended period of time. 2. Good weather resistance: Exterior wall coatings, as they are exposed to the atmosphere, have to withstand wind, sunlight, salt spray corrosion, rain, and temperature fluctuations. Under the continuous impact of these natural environmental factors, the coating is prone to cracking, flaking, peeling, and discoloration, which causes it to lose its original decorative and protective functions. Therefore, it is required that within the specified service life of the exterior wall, the coating should not suffer from the aforementioned types of damage. 3. Good resistance to fouling: Due to the significant differences in environmental conditions across different regions of our country, in cities where heavy industry and mining are well-developed, the high levels of dust and other suspended particles in the air can cause coatings that are prone to fouling to lose their original decorative appearance, thereby affecting the look of buildings. Therefore, exterior wall coatings should have good stain resistance, so that the coating is not easily contaminated or can be easily cleaned if it becomes contaminated. 4. Good water resistance: Exterior wall coatings are exposed to the atmosphere and are frequently subjected to rainwater exposure. Therefore, the exterior wall coating should have good water resistance. 5. Good resistance to mildew: Exterior wall coatings are prone to developing mildew in humid environments. Therefore, the coating is required to inhibit the growth of molds and algae. In addition, depending on the design requirements, higher standards are imposed on exterior wall coatings: for use in various exterior wall insulation systems, such coatings are required to have good elastic elongation properties, so as to better accommodate cracks that may occur in the surface layer due to deformation of the underlying surface, and to cover any minor cracks in that underlying surface ； For exterior wall coatings that are intended to counteract the decorative effects of aluminum-plastic panels, they should also possess a better metallic texture and ultra-long outdoor durability. VII. Main functions and characteristics of interior wall paint The main function of interior wall paint is to decorate and protect indoor walls, making them look beautiful and tidy. The color of interior wall paint should be gentle and soft, creating a comfortable living environment. Therefore, interior wall paint should possess the following characteristics: 1. Rich colors, a fine finish, and good coverage. 2. Good water resistance and scrub resistance. 3. It has a certain level of breathability, allowing it to be applied on relatively humid substrates without issues such as coating bulging. 4. It has good workability; since indoor spaces are relatively small, defects in interior wall coating finishes are easily exposed. Therefore, the coating film should have an excellent appearance, with minimal brush marks and no sagging. 5. It must meet environmental protection requirements; the environmental standards for interior wall coatings need to comply with **mandatory standard requirements (see Table 1-1). Table 1-1: Standards for harmful substances in interior wall coatings. VIII. Types of plasters and their functions. Commonly used interior wall plasters include gypsum plaster, water-resistant plaster, latex plaster, cement plaster, and elastic plaster. Among these, water-resistant plaster boasts high bonding strength and excellent water resistance. Exterior wall putties include ordinary cement putty, flexible water-resistant putty, and others. The appearance types of putty include paste, powder, and two-component types. The traditional function of putty is to level the substrate before applying paint. However, with changes in painting techniques and building substrates, putty has been given additional functions, such as those that help prevent cracks in the substrate, and putty used for preparing tile surfaces before renovating old tiles. IX. How to simply test the quality of paint? 1. Is the outer packaging of the coating proper? Are there instruction manuals and certificates of conformity? Is the address of the manufacturing company indicated? Are there any false markings? Products manufactured by reputable manufacturers come with standard packaging and guaranteed quality ； 2. Open-can condition: If, after opening the can of paint, severe thickening, caking, sedimentation, layering, or an unusual odor is observed, then the quality is poor or the paint has gone bad; if the appearance is uniform and smooth and it remains fluid when stirred, then it is good quality paint ； 3. Construction inspection: During application, if a coating has strong coverage and good leveling properties, it is a good coating ； Otherwise, it is a low-quality paint.