Mastering the Finish
Pre-Treatment for Industrial Coatings
With Dave Morales-Rivas, Service Specialist
What's the most common cause of issues on customer paint lines?
"Pretreatment. Hands down, this is the most common issue we find."
What Improper Pretreatment Can Cause
Coating failures like coating peeling off, poor adhesion and wrinkling caused by contamination underneath the coating, can often be traced back to improper or inconsistent pretreatment. It doesn't matter how good the coating is, if the surface isn't properly cleaned, prepped and dried, the finish will fail.
Although the pretreatment step is critical, it is one of the most overlooked steps in coating performance. Let's learn how our team works to master the finish.
What is Pretreatment?
Pretreatment prepares the surface or substrate before applying coating. It removes dirt, oil, and contaminants and creates a surface profile that paint can stick to. This important step will promote proper adhesion, corrosion resistance, durability, and overall performance of coating.
Common Pretreatment Methods
Chemical Pretreatment
Chemical pretreatment is a multi-step process that prepares the surface through chemical reactions and rinsing. This includes:
- Cleaning: Remove dirt, grease, rust, or mill scale using detergents or solvents.
- Etching: Use acid to clean and create a textured profile.
- Conversion Coating: Apply phosphate or chromate for added corrosion resistance.
- Rinsing: Thoroughly rinse to remove residual chemicals.
- Drying: Fully dry the part, typically in the oven, to prevent moisture-related defects.
Mechanical Cleaning (Blasting)
A physical process using pressurized abrasive media to clean and profile the surface.
- Sandblasting or Shot Blasting: Use high-pressure air to blast plastic, glass, or metal particles.
- Surface Removal: Removes rust, mill scale, old coatings and contaminants.
- Profile Creation: Roughens surface for improved coating adhesion.
Manual Preparation
A hands-on method used by smaller shops or for low-volume parts.
- Initial Cleaning: Wipe down with water-based or solvent cleaners.
- Sanding: Light sanding by hand using 180-grit (or finer) sandpaper.
- Final Cleaning: Wipe again to remove remaining dust and debris.
I often tell people, 'Five minutes of investing in pretreating your substrate can be worth a million dollars.' If it's not done right, you'll spend double to fix it.
How Can Pretreatment Go Wrong?
Avoiding these common mistakes requires attention to detail, proper equipment maintenance, documentation, adherence to best practices and training. By addressing these issues, manufacturers can significantly improve the quality of longevity of industrials coatings while minimizing costly failures.
- Skippping or rushing surface preparation, which leads to inadequate cleaning.
- Uneven application of pretreatment chemicals, resulting in weak spots.
- Improper drying or curing, which leaves residual moisture and interferes with adhesion.
- Using the same pretreatment process for different materials.
- Neglecting equipment maintenance like replacing filters and pumps.
Pretreatment Checklist
David's Pretreatment Checklist
✓ Surface Cleaning: Choose the right cleaning method for your substrate to remove all contaminants.
✓ Chemical Application: Apply chemicals evenly and follow proper dwell and rise cycles.
✓ Drying & Moisture Control: Fully dry parts and ensure no condensation or trapped water is present.
✓ Match Process to Substrate: Don't assume one solution works across substrates.
✓ Maintain Equipment: Inspect and clean filters, nozzles, pumps and tanks regularly and replace worn or damaged parts immediately.
Document everything. Coating issues often don't arise until many months after application, which can make it very difficult to pinpoint the root cause. Documenting your process - pH levels, QC testing, inspections, oven and spray equipment maintenance, etc. - is key.
How Can We Help?
A flawless finish starts before the paint ever hits the part. If you need help identifying issues in your pretreatment process, reach out to Sherwin-WIlliams.
Meet the Contributor
David Morales-Rivas
With more than a decade of experience at Sherwin-Williams, David Morales-Rivas brings deep technical knowledge and a passion for problem-solving to every customer he supports. Based in Phoenix, Arizona, David works with manufacturers across the Southwest, helping them troubleshoot coating challenges, optimize application processes and improve efficiency on their finishing lines.
With a background in retail, David began his journey with Sherwin-Williams as a prebatcher in his local paint facility before earning a promotion into the junior tech rep program. The role grew into a long-term career as he moved into technical service and discovered a love for coatings, chemistry, and continuous improvement.
Now as a Technical Service Specialist, a title reserved for senior reps with in-depth field experience, David serves as a trusted partner to customers, working closely with sales reps, chemists and R&D teams to deliver real-world solutions. He believes in asking questions before jumping to answers, and in always doing what's best for the customer.
He is the perfect example of "Create your Possible™".
Alongside work, David is passionate about learning. He's currently pursuing coursework in sustainability and communications to bring even more value to his customers in an ever-evolving industry.
I represent the brand, but there's an entire team of experts behind me. We're all working toward the same goal - helping the customer win.
How Can Sherwin-Williams Help?
A flawless finish starts before the paint ever hits the part.
Need help identifying issues in your pretreatment process?