Before any paint or coating can adhere effectively to metal, the surface must be prepared. This overview covers the main steps of surface preparation — degreasing, removing rust and mill scale, and final wipe-down — along with the ventilation precautions that accompany solvent use.
Why Preparation Matters
The goal of surface preparation is to create a clean, smooth, and dry surface with good adhesion properties. A finish can only perform as intended when it bonds to the metal beneath it. Skimping on preparation is a common cause of early coating failure — peeling, blistering, and rust forming under the finish.
Degreasing
The first step in surface preparation often involves degreasing. Metal surfaces are frequently contaminated by oils, fats, dirt, and other residues that interfere with the adhesion of paint or coating.
- Method: Use a solvent-based cleaner or a degreaser designed for metal surfaces, apply it thoroughly, and allow it to dwell before rinsing with water as directed.
- Safety: Follow all safety guidelines for handling solvents, including appropriate gloves and eye protection, and work only with adequate ventilation.
Removing Rust and Mill Scale by Mechanical Means
Rust, mill scale, and other surface contaminants can prevent paint from adhering properly.
- Common Methods: Sandblasting, grinding, and wire brushing are typical mechanical approaches.
- Key Point: Remove the contaminants without gouging or marring the metal surface. Deep scratches and gouges can show through the finish or create new corrosion sites.
Final Wipe-Down
Once rust, mill scale, and degreasing are complete, a final wipe-down with a clean, dry cloth helps remove any remaining particles. This step is particularly important when preparing for powder coating, because even tiny particles can cause imperfections in the cured finish. Use clean cloths and change them frequently so they do not redeposit contaminants.
Matching Preparation to the Finish
Different finishes tolerate different surface conditions. Liquid paints are generally more forgiving of minor surface texture, while powder coating and plating demand a very clean, bare surface for best results. When in doubt about how far to take preparation, consult the finish manufacturer's instructions — they are the best guide for their product.
Ventilated Workspace
Always work in a well-ventilated area, especially when using solvents or chemicals for cleaning and degreasing. Proper ventilation helps prevent inhalation of harmful fumes and minimizes other hazards. Store solvents in approved containers away from heat and ignition sources.