Surface PrepApril 2026· 14 min read

Surface Condition and Coating Readiness Following High-Power CW Laser Ablation Coating Removal

Petr Yurchenko

Director, Laser Blasting LLC | Laser Blasting Limited

Practitioner field paper — drawn from multi-year commercial CW LACR operations. Not peer-reviewed academic research.

Abstract

Third-party field measurement data on post-ablation surface condition and coating readiness across five substrate types. Independent third-party surface profile assessment per ASTM D4417 Method C (n=30) recorded a mean profile of 74.9 µm (SD 17.5 µm) — equivalent to commercial blast (SSPC-SP6) and within near-white blast (SSPC-SP10) range. Chloride contamination 1.2–3 µg/cm² against a <5 µg/cm² threshold — PASS.

Surface Profile Data — Field Measurement

Post-ablation surface profile and chloride contamination measurements were conducted by an AMPP Certified Coatings Inspector per ASTM D4417 Method C using a PosiTector Surface Depth Micrometer. Results (n=30): - Mean surface profile: 74.9 µm - Standard deviation: 17.5 µm - Minimum: 44 µm - Maximum: 111 µm - Chloride contamination: 1.2–3 µg/cm² (Specification: <5 µg/cm²) — PASS The mean profile of 74.9 µm falls at the upper end of the commercial blast range (SSPC-SP6: 25–75 µm) and within the near-white blast range (SSPC-SP10: 40–100 µm).

Coating Adhesion — Independent Research

Multiple independent research programs confirm coating adhesion on LACR-prepared steel is equivalent to or superior to abrasive blasted surfaces: Shams et al. (2015): Equivalent or superior adhesion on LACR-treated surfaces vs abrasive blasted samples on high-strength shipbuilding steel. Virginia DOT (VTRC Reports 20-R1 and 26-R10): Coating adhesion on LACR-treated ASTM A36 structural bridge steel was acceptable, met coating manufacturer recommendations, and comparable to grit-blasted surfaces. Moffat et al., University of Virginia / FHWA (2024): Excellent adhesion on legacy bridge steel carrying multi-layer lead-based coatings — qualifying above requirements with no measurable detrimental effects on bulk mechanical properties. US Naval Institute (2024): Paint adhesion to laser-ablated steel yields superior performance compared to sandblasted steel samples.

Surface Chemistry — Fe₂O₃ Layer

CW laser irradiation of structural steel produces a chemically modified surface. Laser irradiation generates iron oxide compounds — principally Fe₂O₃ — on the treated surface. This laser-generated Fe₂O₃ surface exhibits enhanced surface energy and wettability compared to mechanically blasted steel, attributed to surface hydroxyl groups (–OH) that form hydrogen bonds with polar groups in epoxy primer formulations. This chemical adhesion mechanism supplements mechanical interlocking from surface profile — an advantage not available from abrasive blasting.

Prep-to-Prime Window

All prepared steel should receive primer within 8 hours to prevent rust-back per KTA/SSPC-SP COM guidance. Coastal and marine environments: primer application within the same work shift is strongly recommended — ideally within 4–6 hours of ablation completion. If primer application cannot be completed within the same shift, assess for flash rust before coating. A light laser re-pass efficiently removes flash rust and restores the active surface state — a practical advantage over abrasive blasting where re-blasting is required.

Galvanized Steel — Selective Removal

LACR on hot-dip galvanized structural steel documented a key finding: in areas where the zinc coating remained adherent and structurally intact, LACR successfully removed the overlying contamination layer without consuming the underlying zinc — returning those zones to a condition approaching the original zinc patina surface. This selective outcome is operationally significant. Conventional surface preparation methods including abrasive blasting and mechanical grinding typically remove remaining zinc coating indiscriminately, eliminating residual galvanic protection. LACR's ability to selectively treat the contamination layer without consuming structurally sound zinc represents a significant advantage in partial galvanic coating maintenance.

Multi-Substrate Capability

Coating readiness was confirmed across five substrate types: Painted structural steel: 74.9 µm mean profile, chloride PASS — equivalent to commercial blast. Bare corroded steel: Textured bright surface consistent with light-medium blast profile — coating-ready. Galvanized steel — coastal: Refreshed zinc patina in intact zones; bare steel in failed zones — coating-ready with zinc-compatible primer. Concrete: 30°C pre-ablation rising to 54°C post-ablation — short cooling recommended before priming. Timber: Biological contamination removed at correct traverse speed — structural integrity maintained.

Disclaimer: This is a practitioner field paper based on observations from commercial CW LACR operations. Findings are not derived from controlled laboratory testing. Substrate conditions, coating systems, and environmental factors varied across project sites. These observations are intended as a practitioner contribution to the evidence base, complementary to laboratory research rather than a substitute for it.

Author disclosure: Petr Yurchenko is Director of Laser Blasting LLC (Tennessee, USA) and Laser Blasting Limited (Auckland, New Zealand). The SSRT methodology and ThermaLog instrument referenced in this paper are patent-pending. No external funding was received.