Steel structures in road and bridge construction, heavy equipment, and energy and power sectors are constantly exposed to outdoor or corrosive environments, making corrosion a major concern for owners. During factory manufacturing, these facilities undergo high-standard surface treatments such as sandblasting and shot blasting, combined with cathodic protection coatings like thermal spraying zinc and zinc-rich primers, forming a robust anti-corrosion system. The exposed substrate after shot blasting has a rough metal surface, and the cathodic protection coating is in close contact with the substrate, effectively resisting corrosion through the principle of "sacrificing the anode to protect the cathode." However, sandblasting and shot blasting processes are difficult to implement during on-site maintenance: they require complex construction measures, cause facility downtime, and face environmental compliance pressures, ultimately leading to a significant increase in construction time and cost. At this point, only manual or power-tool surface treatment is possible, but this method cannot completely remove oxide scale and old coatings, rendering traditional cathodic protection coatings ineffective and compromising adhesion. Against this backdrop of demand, low-surface-treatment epoxy steel structure repair coatings have emerged – tolerating surface treatment standards as low as St2. they perfectly adapt to the harsh conditions of on-site repairs, becoming a "savior" for corrosion protection in steel structure maintenance. This article will provide a comprehensive understanding of the composition, characteristics, core advantages, and application process of this coating, showing how it achieves strong corrosion protection under low-standard surface treatment.
1. Low-Surface-Treatment Epoxy Coating
1.1 Coating Composition
Low-surface-treatment steel structure repair coating is a two-component modified epoxy powder coating. With modified resin as its core component, it features low surface-treatment compatibility, abrasion resistance, and high solids content, belonging to the thick-film type coating category. Depending on the ambient temperature of the application environment, it also comes with ambient temperature (Std) and winter (WG) curing agents to meet the application needs under different seasons and temperature conditions, thus broadening its applicability.
1.2. Core Features
The biggest highlight of this coating is its extremely low surface preparation requirements, tolerating a minimum standard of St2. It is particularly suitable for scenarios where sandblasting or shot blasting is difficult or impossible, and rust removal can only be done manually or with power tools. Its applications are highly diverse: Primarily used for the repair of anti-corrosion coatings on steel, including roads and bridges, heavy equipment, energy and power, coastal and offshore facilities, providing strong anti-corrosion protection for steel structures in the atmosphere and water; Compatible with various substrates, it can be applied not only to treated steel surfaces but also directly to aged coatings, galvanized layers, and steel surfaces after blasting or water spraying treatments; Flexible application, it can be used alone or in conjunction with other primers and topcoats, and supports high film thickness application, quickly forming a protective layer. More importantly, it exhibits extremely strong adhesion to existing coatings. The modified resin possesses excellent permeability, forming a strong bond when applied to intact existing coatings, with adhesion exceeding 10 MPa. This completely solves the problem of traditional coatings easily peeling off from existing coatings.
2. Core Advantages
The reason why low-surface-treatment Epoxy Powder Coating achieves strong corrosion protection under St2 surface treatment lies in its unique technical design, with significant advantages:
2.1. Penetration + Anchoring Effect, Maximizing Adhesion
Utilizing low-molecular-weight penetration technology, the coating penetrates deep into the tiny pores of the substrate surface and the gaps in the existing coating, forming an "anchoring effect." Like countless tiny hooks, it firmly grasps the substrate, allowing the coating to tightly bond with the substrate and the existing coating. Adhesion typically reaches over 8 MPa, ensuring long-term stability and preventing peeling even on surfaces with low-standard treatment.
2.2 Shielding Protection + Maze Effect, Delaying Corrosion and Erosion
The coating is rich in aluminum foil, which forms a dense shielding layer after curing. Simultaneously, it creates a "maze effect"—external moisture, salt, and chemical corrosive media must navigate through a complex "maze" to penetrate the steel substrate surface. This significantly extends the penetration path, effectively delaying corrosion and erosion and greatly extending the service life of the steel structure.
2.3 Excellent Comprehensive Performance, Adaptable to Complex Environments
The modified resin endows the coating with excellent comprehensive performance: strong adhesion, wear and impact resistance, stable mechanical properties, excellent chemical stability and resistance to high and low temperatures, low shrinkage, and adaptability to various complex corrosive environments such as outdoor, coastal, and underwater environments.
However, a small detail needs attention: after curing, this coating has a smooth surface, high cross-linking density, and a three-dimensional structure with high internal stress and surface energy. Therefore, strict requirements are placed on subsequent coatings; the recommended coating interval must be strictly followed, otherwise the recoating effect will be affected.
3. Application Process
The application of low-surface-conditioning Epoxy Powder Coating is not complex, but to ensure the final anti-corrosion effect, the following key points must be strictly followed, especially the control of surface treatment and application conditions:
3.1. Surface Treatment
For underwater applications, the surface treatment must meet at least Sa2.5 standards, followed by multiple coats to ensure a total dry film thickness of at least 250 microns.
If manual or power tool treatment (such as wire brushes, angle grinders) is used, a minimum St2 standard is acceptable, but the surface must be free of loose or peeling coatings—loose coatings must be thoroughly removed until a solid paint layer is exposed; smooth surfaces require slight roughening to improve adhesion.
All surfaces to be coated must be clean, dry, and free of contaminants, according to ISO 8504:2000. Standard assessment and handling: Remove accumulated dirt with a dry bristle brush; soluble salts must be thoroughly rinsed off with fresh water. If salt water was used during wet spraying, the treated surface must be rinsed thoroughly with fresh water and allowed to dry before applying paint. Slight pinpoint rust is permissible on the sprayed surface, but puddles and standing water must be removed.
3.2. Application Method
Airless spraying is the optimal application method, allowing for maximum film thickness with a single coat and improving application efficiency. If air spraying is used, multiple cross-coatings may be required to form a thick film. Avoid mixing multiple coating methods as much as possible, as this will affect the gloss and surface finish of the coating.
3.3 Construction Conditions
During construction, the surface temperature must be at least 3°C above the dew point to avoid condensation due to temperature differences, which would affect coating adhesion. In outdoor exposure scenarios, long-term exposure of the coating may cause chalking and fading (but this does not affect anti-corrosion performance). Therefore, an additional layer of weather-resistant topcoat is required to enhance both decorative properties and weather resistance. For winter construction, a winter-specific low-temperature curing agent can be used, which can cure rapidly below 10°C, and even in temperatures below 0°C, ensuring the progress and quality of winter construction.
3.4 Substrate Compatibility
Suitable for coating intact, aged alkyd resin, epoxy resin, and polyurethane coatings. It is strictly forbidden to use on surfaces previously coated with chlorinated rubber, vinyl coatings, or other thermoplastic coatings, otherwise insufficient adhesion and coating peeling may occur.
4. Summary
The core value of Epoxy Powder Coating lies in its ability to "adapt to low-standard surface treatments and achieve highly efficient and effective corrosion protection." It perfectly solves the pain point of sandblasting and shot blasting being difficult to implement during on-site maintenance of steel structures. It tolerates surface treatments as low as St2 level and, through low-molecular-weight penetration technology and labyrinth effect design, excels in adhesion, corrosion resistance, and construction flexibility. Whether for on-site maintenance of roads, bridges, and heavy equipment, or for corrosion protection of coastal and offshore facilities, it provides long-term corrosion protection for steel structures thanks to its versatility and excellent comprehensive performance. Moreover, the construction process is relatively simple, supporting both normal and low-temperature construction, meeting the construction needs of different scenarios. To ensure construction effectiveness, the key lies in controlling three points: first, the surface treatment must meet the minimum St2 level standard, ensuring a clean, dry, and non-porous coating; second, select a suitable curing agent according to the construction temperature, prioritizing airless spraying; and third, for outdoor applications, a weather-resistant topcoat is required, strictly adhering to the recoating interval requirements. For owners and contractors, low-surface-treatment epoxy coatings not only reduce on-site repair time and costs but also ensure corrosion protection, making them a practical choice for steel structure maintenance. As the demand for steel structure corrosion protection continues to increase, this coating will undoubtedly play a core role in more fields, safeguarding the long-term protection of steel structure assets.
