Before any painting process, surface preparation plays a decisive role in the durability and adhesion of the coating film. If the surface is not properly cleaned — still contaminated with oil, dust, or rust — the paint will have poor adhesion and peel off after a short time. Following the correct preparation process enhances coating adhesion, increases corrosion resistance, and maintains gloss and durability. It forms the foundation to protect materials and extend their lifespan under various environmental conditions.
FACTORS AFFECTING PAINT ADHESION
Paint adhesion depends not only on the paint quality but also on the surface condition. When the substrate contains oil, dust, or moisture, paint molecules cannot bond tightly to the material. This causes the coating film to blister, flake, or detach under mechanical impact.
Surface roughness and chemical compatibility between the substrate and the coating are equally important. If the surface is too smooth or oxidized, mechanical adhesion is greatly reduced. Therefore, thorough cleaning and proper roughening are essential steps before painting.
COMMON METHODS OF SURFACE PREPARATION
Mechanical and chemical cleaning
Mechanical cleaning is a fundamental step to remove oxides, rust, and contaminants from material surfaces. Common techniques include grinding, sandblasting, or sanding. This process creates the required roughness, improving the mechanical grip and uniformity of the paint film.
Meanwhile, chemical cleaning is performed using acids, alkalis, or specialized degreasing agents. Its purpose is to completely remove oil and remaining rust. These two methods are often combined to achieve the SSPC-SP10 near-white metal standard. Once the surface meets this standard, the coating adheres better and remains stable for a longer time.
Solvent cleaning and etching
For lightweight materials such as wood, plastic, or composites, aggressive mechanical abrasion may cause damage. In these cases, solvent cleaning is used to remove oil, wax, or silicone residues. It also enhances adhesion for solvent-based and polyurethane coatings.
Additionally, etching with mild acids like HCl or H₂SO₄ creates micro-roughness on the surface. This increases contact area and bonding strength between the substrate and coating. After etching, the surface must be neutralized and thoroughly dried to avoid adverse chemical reactions.
Phosphating and adhesion primers
Phosphating is a surface treatment for metals using chemicals that form an inorganic phosphate layer. This layer enhances corrosion resistance and improves bonding between metal and paint. It is widely applied in powder coating, automotive, and mechanical industries.
For difficult substrates such as aluminum, stainless steel, or plastics, using adhesion primers is indispensable. Primers like epoxy, etch, or PU types act as an intermediate layer, ensuring chemical bonding between the base and topcoat. Proper priming provides stable, moisture-resistant coatings with minimal risk of peeling or cracking.
ENVIRONMENTAL CONDITIONS AFFECTING PAINT APPLICATION
Temperature and humidity during application have a direct impact on coating quality. High humidity causes condensation on surfaces, which prevents proper bonding. Similarly, if the temperature is too low, solvents evaporate slowly, leaving the coating soft or partially cured.
The time interval between surface preparation and painting also requires careful control. For metals, this should not exceed six hours to prevent re-oxidation. Application should take place in a dry, clean, and dust-free environment to ensure excellent adhesion and aesthetic finish.
VICHEM – AUTHORIZED DISTRIBUTOR OF CERTIFIED CHEMICAL ADDITIVES IN VIETNAM
Vichem is a distributor of chemical additives from major brands such as Covestro, Buhler, Sinopec,… with full information according to legal regulations in Vietnam. We not only provide quality products but also provide after-sales services that meet international standards. Services include:
- Technical consultation: Assisting customers in selecting suitable chemical solutions for their intended applications.
- Color testing and formulation: Vichem’s technical team performs lab tests to ensure color accuracy and consistency with design specifications.
- On-site application support: Partnering with clients during production to ensure optimal efficiency and coating performance.
For more information about our products and solutions, please contact us through the following channels:
📞 Hotline: 08 1790 1790
📧 Email: contact@vichem.vn
🔎 LinkedIn: Vichem JSC
🌐 Website: www.vichem.vn
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