CSLB C-33 Painting & DecoratingSurface PreparationHard
A painting contractor is preparing a concrete floor in a commercial garage that has oil stains and grease residue. The floor will be coated with an epoxy-based floor coating. Which of the following is the most critical surface preparation step to ensure proper adhesion of the epoxy coating?
- APressure wash the floor with plain water to remove loose dirt and debris.
- BGrind the concrete surface with a diamond grinder to create a surface profile.
- CApply a strong degreaser and scrub thoroughly, followed by etching with phosphoric acid.
- DApply a concrete sealer to encapsulate the oil and grease before coating.
Show answer & explanationAnswer & explanation
Correct answer: B. Grind the concrete surface with a diamond grinder to create a surface profile.
For epoxy coatings on concrete, achieving a proper surface profile (CSP 2-3) is critical for mechanical adhesion. Grinding with a diamond grinder effectively removes contaminants like oil and grease while simultaneously creating the necessary profile. While degreasing and etching are important, grinding is superior for heavy contamination and optimal epoxy adhesion.
Why the other options are wrong
- A. Pressure washing with plain water is insufficient to remove oil/grease or create the necessary profile for epoxy.
- C. Degreasing and etching are good for light contamination and creating some profile, but often insufficient for heavy oil/grease or optimal epoxy adhesion compared to grinding.
- D. Applying a sealer over oil/grease will trap the contaminants, preventing proper adhesion of the epoxy coating.
Concrete Surface Profile (CSP)
A measure of the surface roughness of concrete, critical for mechanical adhesion of coatings, especially epoxies.
- Achieved through mechanical means (grinding, shot blasting).
- Measured by ICRI (International Concrete Repair Institute) standards.
- Higher CSP (e.g., CSP 2-3) indicates rougher surface, better adhesion.
Memory trick: Grind it rough, clean it well, then epoxy will stick like hell.