CSLB C-33 Painting & DecoratingSurface PreparationMedium
A painting contractor is preparing a new, unpainted concrete floor in a commercial kitchen. The concrete has been cured for 28 days. To ensure proper adhesion of an epoxy coating, what is the most critical surface preparation step before applying the primer?
- AApplying a curing compound to harden the surface.
- BPower washing with plain water.
- CApplying a concrete densifier.
- DAcid etching to achieve a CSP 2-3 profile.
Show answer & explanationAnswer & explanation
Correct answer: D. Acid etching to achieve a CSP 2-3 profile.
For new concrete floors receiving an epoxy coating, achieving a proper surface profile (typically CSP 2-3) is critical for mechanical adhesion. Acid etching (or grinding/shot blasting) creates this profile by opening the concrete's pores. Plain power washing cleans but doesn't profile. Densifiers and curing compounds alter the surface chemistry in ways that can hinder, rather than help, epoxy adhesion if not properly removed.
Why the other options are wrong
- A. Applying a curing compound is done after concrete placement to aid curing; if present, it must be removed, not applied, before epoxy coating.
- B. Power washing with plain water cleans the surface but does not create the necessary abrasive profile for epoxy adhesion.
- C. Concrete densifiers improve surface hardness but do not create the necessary profile for epoxy adhesion and can interfere with bonding if not properly prepared.
Concrete Floor Prep for Epoxy
Proper surface profiling (e.g., CSP 2-3 via acid etching, grinding, or shot blasting) is critical for mechanical adhesion of epoxy coatings to concrete floors.
- Epoxy requires a mechanical bond.
- CSP standards define surface roughness.
- Acid etching or grinding achieves profiling.
Memory trick: Epoxy's embrace needs concrete's coarse face, not just a clean space.