Surface Preparation
Why preparation dominates outcomes
Most coating failures trace to surface preparation. You must understand what each preparation method removes and what profile it creates. Solvent cleaning removes oil and grease but no rust or mill scale; hand and power tool cleaning remove loose material but leave tight mill scale and salts; abrasive blast cleaning removes mill scale, rust, and old coating while creating an anchor profile.
Abrasive blasting concepts
Know the difference between surface cleanliness (how much contamination remains) and surface profile (anchor pattern roughness). These are independent - a blast can achieve a white-metal finish with too shallow a profile. Understand abrasive types (metallic vs. non-metallic, expendable vs. recyclable), nozzle pressure and angle effects, and why nozzle distance and angle affect productivity and profile. Recognize the NACE/SSPC abrasive blast cleanliness grades (e.g., white metal, near-white, commercial, brush-off) and their typical descriptions, and the corresponding hand/power tool grades. Traps include assuming a higher cleanliness grade guarantees adequate profile, or thinking a visible profile equals a clean surface.
Contamination and inspection
Salts (chlorides, sulfates) drive osmotic blistering and premature failure; they are detected by conductivity or specific ion tests on the prepared surface. Soluble salt limits are project-specific. Ambient conditions (dew point, surface temperature, humidity) govern when preparation and coating may proceed.
Worked example: If surface temperature is 50°F and dew point is 47°F, the surface is only 3°F above dew point - below the common 5°F minimum, so blasting and coating should be halted.