High-elasticity enhanced polyurea coating for concrete protection and construction method of high-elasticity enhanced polyurea coating

Abstract

The invention discloses a high-elasticity enhanced polyurea coating for concrete protection and a construction method of the high-elasticity enhanced polyurea coating, and belongs to the technical field of polyurea coatings. The coating adopts a two-component system, a specific isocyanate component reacts with polyol to prepare a component A, and polyether amine with a specific structure, a functional chain extender, reinforcing filler and the like are compounded to prepare a component B. Compared with the prior art, the core of the invention is to construct a rigid-flexible interpenetrating structure in a polymer network through accurate design and synergistic compounding of the molecular structure of the chain extender, so that the contradiction that the traditional polyurea coating is easy to embrittle due to too strong rigidity or insufficient in support due to residual toughness is effectively solved. The coating can be constructed in a brush coating mode, operation is easy and convenient, and the obtained coating has excellent impact resistance, high elasticity and good heat-resistant stability and can meet the long-acting protection requirement of a concrete structure in a complex and severe environment.

Description

Technical Field

[0001] This invention relates to the field of polyurea coating technology, and in particular to a highly elastic reinforced polyurea coating for concrete protection and its application method. Background Technology

[0002] Concrete structures are susceptible to environmental erosion and physical wear during service, making protective coatings a crucial means of extending their lifespan. Among these, polyurea coatings have become an important choice for concrete protection due to their excellent waterproof, abrasion-resistant, and impact-resistant properties. In existing technologies, general-purpose polyurea coatings are mostly based on the reaction of traditional diisocyanates (such as MDI) with amino-terminated polyethers, often using fast-reacting chain extenders such as diethyltoluene diamine (DETDA), and are applied using high-pressure spraying equipment to form a rapidly curing coating. While these coatings offer basic protection, they generally suffer from insufficient toughness, brittleness, or poor weather resistance, and their reliance on specialized equipment limits their application scenarios. Developing a polyurea coating that combines high elasticity, high strength, and ease of application is of great significance for improving the reliability and versatility of concrete protection.

[0003] Patent CN119191991A discloses a bio-based sprayable flame-retardant polyurea coating, characterized by the use of bio-based aliphatic polyamine chain extenders and bio-based isocyanate PDI, emphasizing environmental protection and flame-retardant properties. However, this technology focuses on achieving sustainability through bio-based raw materials and does not address the balance between rigidity and toughness of the coating under extreme mechanical loads, and its spraying process requires sophisticated equipment. Another patent, CN120059574A, relates to a modified high-strength single-component polyurea coating, which improves performance through complex modification methods such as introducing nanofibers and metal coordination microgels. However, this preparation process is cumbersome and costly, and as a single-component system, its curing efficiency and the overall mechanical properties of the final coating may be limited.

[0004] In summary, existing technologies either fail to effectively resolve the core contradiction of balancing rigidity and toughness within polyurea coatings, have complex preparation processes that hinder industrial application, or limit application methods. Therefore, there is an urgent need for a polyurea coating that can be prepared using a simple process, is suitable for conventional brush application, and simultaneously achieves synergistic enhancement of high elasticity and high strength to meet the demanding and diverse long-term protection requirements of concrete structures. Summary of the Invention

[0005] In order to solve the problems of the prior art, the present invention aims to provide a high-elasticity composite reinforced concrete protective polyurea coating with strong impact resistance and heat resistance, and a method for preparing the same.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for preparing a highly elastic reinforced polyurea coating for concrete protection includes the preparation of component A and component B: Preparation of component A: HDI trimer and MDI prepolymer were mixed, and then dehydrated polytetrahydrofuran ether was added. The mixture was stirred, heated and subjected to atmospheric pressure treatment, and then cooled and discharged to obtain component A.

[0007] Preparation of component B: Polyetheramine and chain extender are stirred and mixed. Aramid pulp, coupling agent, dispersant and leveling agent are added while stirring. The mixture is thoroughly mixed, heated and stirred, and finally cooled and discharged to obtain component B.

[0008] A further preferred embodiment of the method for preparing the highly elastic reinforced polyurea coating for concrete protection includes the preparation of component A and component B, in parts by weight: Preparation of component A: Mix 30-50 parts of HDI trimer and 30-50 parts of MDI prepolymer to form a polyisocyanate mixture. Then, add 15-25 parts of dehydrated polytetrahydrofuran ether, heat and pressurize under stirring, cool and discharge to obtain component A, which is then sealed and stored for later use.

[0009] Preparation of component B: Mix 60-120 parts of polyetheramine and 10-30 parts of chain extender. While stirring, add 1-5 parts of aramid pulp, followed by 1-5 parts of coupling agent, 0.5-2 parts of dispersant, and 0.3-0.8 parts of leveling agent. Mix thoroughly and evenly. Heat and stir the mixture, and finally cool and discharge to obtain component B.

[0010] The polyetheramine is at least one of polyetheramine JEFFAMINE® D-2000 and polyetheramine T403.

[0011] The leveling agent is at least one of BYK-354 and BYK-333.

[0012] The dispersant is selected from at least one of BYK-164, BYK-163, and BYK-110.

[0013] The coupling agent is at least one of γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and γ-aminoethylaminopropyltrimethoxysilane.

[0014] The chain extender is at least one selected from dimethylthiotoluene diamine, isophorone diamine, 4,4'-diaminodicyclohexylmethane, 1,3-cyclohexanedimethylamine, trimethylhexanediamine, 4,4'-methylenebis(3-chloro-2,6-diethylaniline), 1,4-cyclohexanediamine, and 4,4'-diaminodiphenyl ether.

[0015] Preferably, the chain extender is a combination of 4,4'-diaminodicyclohexylmethane and trimethylhexanediamine in a mass ratio of 0.5-2:0.5-2.

[0016] Preferably, the chain extender is composed of 4,4'-diaminodicyclohexylmethane, trimethylhexanediamine and 4,4'-diaminodiphenyl ether in a mass ratio of 0.5-2:0.5-2:0.1-0.3.

[0017] The preparation method of component A involves heating to 70-90℃, treating under normal pressure for 1-5 hours, and then cooling to 0-50℃ before discharging.

[0018] The preparation method of component B involves heating to 60-80℃, stirring continuously for 0.5-3 hours, and finally cooling to 0-50℃ for discharge.

[0019] The application method for polyurea coatings is as follows: First, apply an epoxy sealing primer to the concrete substrate that has been derusted, repaired, and ensured to be dry and firm. After application, cure under standard conditions until surface dry. The coating amount of epoxy sealing primer is 0.1-0.3 kg / m². 2 For critical weak areas, the polyurea coating prepared according to this invention is used for filling and scraping. The polyurea coating is obtained by mixing component A and component B evenly in a mass ratio of 0.5-2:0.5-2. After the primer surface has completely dried, the polyurea coating is scraped and applied completely with a scraper. After the coating has cured for 5-20 hours, a second coat is applied. Immediately after applying the second coat of polyurea coating, fiberglass mesh is laid and smoothed with a scraper to ensure that the mesh is fully impregnated and adhered. A third coat of polyurea coating is applied after the second coat has dried, scraping until the outline of the base fabric is no longer visible to the naked eye. Finally, the coating amount of the polyurea layer is ensured to be 1.5-3 kg / m². 2 Finally, after the polyurea layer is completely dry, apply a pressure of 0.1-0.25 kg / m². 2 Apply an appropriate amount of aliphatic polyurethane topcoat to form a weather-resistant protective layer.

[0020] The starting point of this invention is to completely abandon conventional chain extenders (such as DETDA) that dominate traditional polyurea systems but have significant performance shortcomings (such as high toxicity, easy yellowing, and poor flexibility). Instead, based on the correspondence between molecular structure and final performance, two types of chain extenders with highly targeted functions were screened from the vast amine compounds: one type is a rigid chain extender that can construct a rigid structure with high strength and high thermal stability, and the other type is a flexible chain extender that can impart extreme elasticity and impact resistance. This step lays the molecular foundation for high performance, rather than a simple improvement on existing materials.

[0021] Based on precise selection, the most innovative design of this invention lies in the bold combination of rigid and flexible chain extenders with vastly different properties. The core idea is to allow the rigid molecular chains to act as a framework providing strength and heat resistance, while simultaneously allowing the flexible molecular chains to act as a muscular layer, encapsulating and wrapping around it to dissipate stress. This design is not a simple mixture, but rather aims to achieve a synergistic effect by designing and controlling the molecular level to allow the two components to form a rigid-flexible interpenetrating network structure during the curing process, thereby improving the coating's performance indicators.

[0022] To achieve optimal performance, this invention introduces a functional chain extender containing special ether bonds into the optimized rigid-flexible composite system. The underlying design principle is that the introduction of ether bonds not only further enhances the flexibility and mobility of the molecular chains, but also, through their combination with benzene rings, imparts dynamic stability to the entire coating. This design allows the coating network to dissipate energy through physical deformation when subjected to external forces or heat, and may also achieve more intelligent stress distribution and energy dissipation at the intermolecular force level, thereby further improving the overall protective performance of the coating.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects: 1) This invention, through unique molecular design, fundamentally solves the contradiction between high strength and high elasticity in traditional materials. The resulting polyurea coating possesses both the toughness to withstand severe impacts and the rigidity to support heavy loads, achieving a comprehensive performance balance that was previously unattainable, and significantly extending its service life.

[0024] 2) This invention optimizes the material's reaction characteristics and provides a suitable operating window, making it particularly suitable for conventional construction methods such as manual brushing. It reduces reliance on complex and expensive equipment, making the application of high-performance protective coatings more convenient and flexible, and broadening its application scenarios.

[0025] 3) This invention endows polyurea coatings with excellent high and low temperature resistance and anti-aging capabilities, enabling them to maintain stable performance over long periods in harsh outdoor environments. This strong environmental adaptability ensures durable and reliable protective effects and reduces maintenance costs. Detailed Implementation

[0026] Some material parameters and their sources: MDI prepolymer, model: MDI prepolymer Specflex NE466, NCO content (%): 26.0-27.0, viscosity (25℃, mPas): 150-230, brand: DOW.

[0027] HDI trimer is hexamethylene diisocyanate polyisocyanate, brand: WANHUA, model: WANNATEHT 600, NCO content (%): 23.0±0.5.

[0028] Polytetrahydrofuran ether, model: PTMG 1800, molecular weight: 1800±100, brand: Mitsubishi, Japan.

[0029] JEFFAMINE® D-2000 polyetheramine, brand: Huntsman, CAS No.: 9046-10-0.

[0030] Polyetheramine T403, model: T403, brand: Huntsman.

[0031] Aramid pulp, fineness: 2.02 dtex, strength: 20 cN / dtex, elongation: 3.5-5%, density (g / cm³) 3 ): Approximately 1.4, specific surface area (m²) 2 / g:5-8.

[0032] For the epoxy sealing primer, use Jotafloor Sealer epoxy floor sealer.

[0033] Fiberglass mesh, wire diameter: 0.8mm, size: 1.2×3m, mesh size: 60mm.

[0034] Aliphatic polyurethane topcoat, using International Paint's Interthane 990E.

[0035] All other raw materials used in the embodiments and comparative examples of this invention are commercially available products. Example 1

[0036] A method for preparing a highly elastic reinforced polyurea coating for concrete protection includes the preparation of component A and component B, in parts by weight: Preparation of component A: 40 parts of HDI trimer and 40 parts of MDI prepolymer were mixed to form a polyisocyanate mixture. Then, 20 parts of dehydrated polytetrahydrofuran ether were added. The mixture was heated to 85°C under stirring and treated under normal pressure for 2 hours. The mixture was then cooled to 40°C and discharged to obtain component A, which was then sealed and stored for later use.

[0037] Preparation of component B: Mix 60 parts of polyetheramine JEFFAMINE® D-2000, 30 parts of polyetheramine T403, and 20 parts of chain extender. While stirring, add 3 parts of aramid pulp, followed by 2 parts of γ-aminopropyltriethoxysilane, 1.2 parts of BYK-164, and 0.5 parts of BYK-354. Mix thoroughly and evenly. Heat the mixture to 70°C and stir continuously for 1.5 hours. Finally, cool it to 40°C and discharge to obtain component B.

[0038] The chain extender is dimethylthiotoluenediamine. Example 2

[0039] The preparation method of a highly elastic reinforced polyurea coating for concrete protection is basically the same as that in Example 1, except that the chain extender is isophorone diamine. Example 3

[0040] The preparation method of a highly elastic reinforced polyurea coating for concrete protection is basically the same as that in Example 1, except that the chain extender is 4,4'-diaminodicyclohexylmethane. Example 4

[0041] The preparation method of a highly elastic reinforced polyurea coating for concrete protection is basically the same as that in Example 1, except that the chain extender is 1,3-cyclohexanedimethylamine. Example 5

[0042] The preparation method of a highly elastic reinforced polyurea coating for concrete protection is basically the same as that in Example 1, except that the chain extender is trimethylhexanediamine. Example 6

[0043] The preparation method of a highly elastic reinforced polyurea coating for concrete protection is basically the same as that in Example 1, except that the chain extender is 4,4'-methylenebis(3-chloro-2,6-diethylaniline). Example 7

[0044] The preparation method of a highly elastic reinforced polyurea coating for concrete protection is basically the same as that in Example 1, except that the chain extender is 1,4-cyclohexanediamine. Example 8

[0045] The preparation method of a highly elastic reinforced polyurea coating for concrete protection is basically the same as that in Example 1, except that the chain extender is composed of 4,4'-diaminodicyclohexylmethane and trimethylhexanediamine in a mass ratio of 1:1. Example 9

[0046] The preparation method of a highly elastic reinforced polyurea coating for concrete protection is basically the same as that in Example 1, except that the chain extender is composed of dimethylthiotoluene diamine and 4,4'-methylenebis(3-chloro-2,6-diethylaniline) in a mass ratio of 1:1. Example 10

[0047] The preparation method of a highly elastic reinforced polyurea coating for concrete protection is basically the same as that in Example 1, except that the chain extender is composed of 1,4-cyclohexanediamine and trimethylhexanediamine in a mass ratio of 1:1. Example 11

[0048] The preparation method of a highly elastic reinforced polyurea coating for concrete protection is basically the same as that in Example 1, except that the chain extender is composed of 4,4'-diaminodicyclohexylmethane, trimethylhexanediamine and 4,4'-diaminodiphenyl ether in a mass ratio of 1:1:0.2.

[0049] Comparative Example 1 The preparation method of a highly elastic reinforced polyurea coating for concrete protection is basically the same as that in Example 1, except that the chain extender is diethyltoluenediamine.

[0050] Application Example 1 The method for applying the polyurea coating by brushing is as follows: First, apply an epoxy sealing primer to the rust-removed, repaired, and thoroughly dried and solidified concrete substrate. After application, cure under standard conditions until surface dry. The epoxy sealing primer application rate is 0.2 kg / m². 2 For critical weak points, the polyurea coating prepared according to this invention is used for filling and scraping. The polyurea coating is obtained by mixing component A and component B in a 1:1 mass ratio. After the primer surface has completely dried, the polyurea coating is scraped and applied completely with a scraper. After the coating has cured for 12 hours, a second coat is applied. Immediately after applying the second coat of polyurea coating, fiberglass mesh is laid and smoothed with a scraper to ensure the mesh is fully saturated and adhered. A third coat of polyurea coating is applied after the second coat has dried, scraped until the outline of the mesh is no longer visible to the naked eye, ultimately ensuring a polyurea layer coverage of 2.2 kg / m². 2 Finally, after the polyurea layer is completely dry, it is applied at 0.18 kg / m². 2 Apply an appropriate amount of aliphatic polyurethane topcoat to form a weather-resistant protective layer.

[0051] Test Example 1 Impact resistance test: To evaluate the toughness of the polyurea coatings prepared in the embodiments and comparative examples of this invention under high-speed impact after application, the coatings were applied to a 50mm × 120mm × 0.3mm tinplate with a thickness of 0.5 ± 0.05mm and cured for 7 days. An impact testing machine (1000g hammer, 8mm punch diameter) was used. The sample was placed on the base of the impact testing machine, with the punch aligned with the coating surface. The hammer was released to impact the coating from different heights, and the coating was checked for cracking or peeling. The maximum impact height (cm) from which the coating did not crack or peel was recorded.

[0052] Three samples were tested in each group, and the average value was taken. The impact resistance should be ≥50cm, demonstrating excellent toughness. The test results are summarized in Table 1.

[0053] Table 1 Experimental protocol Maximum impact height (cm) Example 1 58 Example 2 55 Example 3 48 Example 4 62 Example 5 65 Example 6 56 Example 7 50 Example 8 68 Example 9 58 Example 10 63 Example 11 72 Comparative Example 1 45 Test Example 2 Heat resistance test: This method aims to simulate the coating's ability to resist softening, flowing, blistering, and peeling from the substrate when subjected to solar radiation or localized high temperatures in real-world usage environments.

[0054] Refer to the heat resistance test in GB / T 16777-2008 "Test Methods for Waterproof Coatings for Buildings" and make adaptive improvements.

[0055] Quantitatively determine the coating’s ability to resist vertical deformation at specific high temperatures and time periods.

[0056] Three cement mortar slabs (compliant with JC / T 547-2017 standard) measuring 150mm × 70mm × 10mm were prepared for each group. The surfaces were flat, clean, and dry. A complete coating system was formed on the cement mortar slabs by strictly following the construction method provided in Application Example 1 of this invention (including primer application, three coats of polyurea coating, etc.). The coated samples were cured for 7 days under standard test conditions (temperature 23±2℃, relative humidity 50±10%).

[0057] Preheat the drying oven to 130±2℃. Measure the initial coating thickness d0 at the lower end of the sample using vernier calipers. Place the sample on a metal frame with the coated surface facing the hot air direction, and quickly close the drying oven door. Continue heating at 130±2℃ for 8 hours. After heating, immediately remove the sample, place it horizontally under standard test conditions, and cool to room temperature. After cooling, measure the coating thickness d1 at the same location at the lower end of the sample again.

[0058] Thickness change rate calculation: Thickness change rate = (d1 - d0) / d0 × 100% The thickness variation rate should be ≤5%. This indicates that the coating has excellent resistance to flow and sag at high temperatures.

[0059] The relevant test data are summarized in Table 2.

[0060] Table 2 Experimental protocol Thickness change rate (%) Example 1 4.2 Example 2 3.8 Example 3 2.5 Example 4 4.5 Example 5 5.0 Example 6 3.5 Example 7 3.0 Example 8 2.3 Example 9 3.8 Example 10 3.9 Example 11 1.5 Comparative Example 1 6.8 In the test data of this invention, the performance differences among the various embodiments may lie in the precise design of the chain extender molecular structure and its synergistic mechanism. Specifically, Example 5 (trimethylhexanediamine) performed best in the impact resistance test, possibly because its branched aliphatic structure introduced a large amount of free volume and molecular chain flexibility into the polymer network. This structure can effectively absorb and dissipate impact energy through rapid chain segment rotation and conformational changes, thereby significantly improving toughness. Example 3 (4,4'-diaminodicyclohexylmethane) had a lower thickness change rate in the heat resistance test, possibly due to its highly symmetrical rigid ring structure forming regular and strong hard segment microregions, which act as a stable molecular skeleton, effectively limiting the thermal motion of the molecular chains at high temperatures and resisting softening deformation. Example 8 exhibited a synergistic effect, the mechanism of which may lie in the hard segment microregions formed by the rigid 4,4'-diaminodicyclohexylmethane acting as physical crosslinking points to provide strength support, while the soft segment network of flexible trimethylhexane disperses stress through chain segment movement. The combination of the two forms a rigid-flexible interpenetrating network structure, achieving a balanced optimization of strength and toughness. In contrast, the combination of Examples 9 and 10 failed to produce significant synergistic gains due to insufficient functional overlap or complementarity in their molecular structures. Example 11, by introducing 4,4'-diaminodiphenyl ether, further improved performance. The key likely lies in the fact that the introduction of the ether bond not only enhances the flexibility and mobility of the molecular chain, but also, with the benzene ring forming a diphenyl ether structure, endows the entire system with excellent thermal stability and dynamic reversibility, constructing a more complete stress dissipation path and thermal stability barrier, thereby improving impact resistance and heat resistance. In summary, the performance advantage of this invention is that by precisely controlling the structural units of the chain extender and their synergistic combination, a comprehensive improvement in the mechanical strength, toughness, and heat resistance of the coating is achieved at the molecular level.

Claims

1. A method for preparing a highly elastic reinforced polyurea coating for concrete protection, characterized in that, This includes the preparation of component A and component B: Preparation of component A: HDI trimer and MDI prepolymer were mixed, and then dehydrated polytetrahydrofuran ether was added. The mixture was stirred, heated and subjected to atmospheric pressure treatment, and then cooled and discharged to obtain component A. Preparation of component B: Polyetheramine and chain extender are stirred and mixed. Aramid pulp, coupling agent, dispersant and leveling agent are added while stirring. The mixture is thoroughly mixed, heated and stirred, and finally cooled and discharged to obtain component B.

2. The method for preparing the highly elastic reinforced polyurea coating for concrete protection as described in claim 1, characterized in that, Including the preparation of component A and component B, in parts by weight: Preparation of component A: Mix 30-50 parts of HDI trimer and 30-50 parts of MDI prepolymer to form a polyisocyanate mixture. Then, add 15-25 parts of dehydrated polytetrahydrofuran ether, heat and pressurize under stirring, cool down and discharge to obtain component A, which is then sealed and stored for later use. Preparation of component B: Mix 60-120 parts of polyetheramine and 10-30 parts of chain extender. While stirring, add 1-5 parts of aramid pulp, followed by 1-5 parts of coupling agent, 0.5-2 parts of dispersant, and 0.3-0.8 parts of leveling agent. Mix thoroughly and evenly. Heat and stir the mixture, and finally cool and discharge to obtain component B.

3. The method for preparing the highly elastic reinforced polyurea coating for concrete protection as described in claim 1 or 2, characterized in that, The polyetheramine is at least one of polyetheramine JEFFAMINE® D-2000 and polyetheramine T403; the leveling agent is at least one of BYK-354 and BYK-333.

4. The method for preparing the highly elastic reinforced polyurea coating for concrete protection as described in claim 1 or 2, characterized in that, The dispersant is selected from at least one of BYK-164, BYK-163, and BYK-110.

5. The method for preparing the highly elastic reinforced polyurea coating for concrete protection as described in claim 1 or 2, characterized in that, The coupling agent is at least one of γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and γ-aminoethylaminopropyltrimethoxysilane.

6. The method for preparing the highly elastic reinforced polyurea coating for concrete protection as described in claim 1 or 2, characterized in that, The chain extender is at least one selected from dimethylthiotoluene diamine, isophorone diamine, 4,4'-diaminodicyclohexylmethane, 1,3-cyclohexanedimethylamine, trimethylhexanediamine, 4,4'-methylenebis(3-chloro-2,6-diethylaniline), 1,4-cyclohexanediamine, and 4,4'-diaminodiphenyl ether.

7. The method for preparing the highly elastic reinforced polyurea coating for concrete protection as described in claim 1 or 2, characterized in that, The chain extender is composed of 4,4'-diaminodicyclohexylmethane and trimethylhexanediamine in a mass ratio of 0.5-2:0.5-2.

8. The method for preparing the highly elastic reinforced polyurea coating for concrete protection as described in claim 1 or 2, characterized in that, In the preparation method of component A, the heating and atmospheric pressure treatment and the cooling and discharge are carried out by heating to 70-90℃, atmospheric pressure treatment for 1-5 hours, and cooling to 0-50℃ for discharge; in the preparation method of component B, the heating and stirring and the cooling and discharge are carried out by heating to 60-80℃, stirring continuously for 0.5-3 hours, and finally cooling to 0-50℃ for discharge.

9. A highly elastic reinforced polyurea coating for concrete protection, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. A construction method, characterized in that, The high-elasticity reinforced polyurea coating for concrete protection as described in claim 9 is used. The specific construction method is as follows: First, apply an epoxy sealing primer to the concrete substrate that has been derusted, repaired, and ensured to be dry and firm. After application, cure under standard conditions until surface dry. The epoxy sealing primer application rate is 0.1-0.3 kg / m². 2 For critical weak points, fill and scrape with the high-elasticity reinforced polyurea coating for concrete protection as described in claim 9. The polyurea coating is obtained by mixing component A and component B evenly in a mass ratio of 0.5-2:0.5-2. After the primer surface has completely dried, apply a complete coat of polyurea coating with a scraper. After the coating has cured for 5-20 hours, apply a second coat. Immediately after applying the second coat of polyurea coating, lay down the fiberglass mesh and smooth it with a scraper to ensure the mesh is fully saturated and adhered. Apply a third coat of polyurea coating after the second coat has dried, scraping until the outline of the base fabric is no longer visible to the naked eye. Finally, ensure that the coating amount of the polyurea layer is 1.5-3 kg / m². 2 Finally, after the polyurea layer is completely dry, apply a pressure of 0.1-0.25 kg / m². 2 Apply an appropriate amount of aliphatic polyurethane topcoat to form a weather-resistant protective layer.