Field Note

Protective Coatings and Surface Treatment

Protective coatings prevent substrate corrosion and degradation across environmental stressors. This note documents exposure conditions, coating types and selection criteria, substrate preparation procedures, application methods, and durability expectations for platforms traversing documented routes. Comprehensive performance data enables specification of appropriate coating systems and maintenance schedules based on environmental severity.

Exposure Conditions on Documented Routes

Platforms traverse varied terrain and environmental conditions. Protective coatings must address multiple concurrent stressors. Severity ratings derived from observed frequency and intensity across documented routes.

Route Primary Exposure Types Impact Frequency (per km) Immersion Hours (per traverse) UV Index Range Severity
Alpine Traverse Gravel impact, freeze-thaw, UV, vegetation abrasion 18–24 2–4 8–11 High
Coastal Exchange Salt spray, water immersion, UV, sand abrasion 12–16 6–12 9–12 High
Desert Meridian Gravel impact, UV, thermal cycling, sand abrasion 14–20 0–1 10–13 High
Forest Loop Vegetation abrasion, moisture, UV (filtered), impact 8–12 3–6 4–7 Moderate
Plateau Corridor Gravel impact, wind-driven abrasion, UV 16–22 1–2 7–10 High
Impact frequency measured by strike count on leading surfaces per kilometer traveled. Immersion hours represent cumulative water contact time during single complete traverse. UV index reflects observed maximum values during midday transit.
Coating Types

Three primary coating categories exist and are applied based on exposure severity and substrate material. Selection depends on expected service environment and reapplication tolerance.

Polymer-Based Coatings

Two-part polymer compound systems. High impact resistance. Applied via spray or brush. Forms continuous film layer. Thermal curing at ambient or elevated temperature. Typical thickness range 0.5–1.5 mm.

Mineral-Based Coatings

Ceramic particle suspension systems. Heat-cured to form hard, brittle surface. Exceptional UV and abrasion resistance. Applied via spray application only. Typical thickness range 0.2–0.8 mm.

Petroleum-Derived Coatings

Penetrating oil treatment systems. Corrosion inhibition via molecular displacement of moisture. Reapplication required at regular intervals. Applied via immersion, spray, or brush. Typical thickness range 0.01–0.05 mm.

Coating Type Application Method Thickness (mm) Impact Resistance (J) Abrasion Rate (mm/1000 km) UV Stability Water Resistance
Polymer-Based Spray or brush 0.5–1.5 8–14 0.04–0.08 Good (3–5 years) Excellent
Mineral-Based Spray 0.2–0.8 4–7 0.02–0.04 Excellent (5–7 years) Excellent
Petroleum-Derived Immersion, spray, or brush 0.01–0.05 2–3 0.08–0.15 Fair (1–2 years) Good
Impact resistance measured via drop-weight pendulum test (J = joules). Abrasion rate derived from field observation using standardized gravel-spray apparatus. UV stability expressed as observed color-change interval under continuous exposure.
Substrate Preparation

Surface cleanliness and profile determine coating adhesion and durability. Preparation procedures vary by substrate material. All steps must be completed within environmental window constraints.

Steel Substrates

  1. Remove rust and scale via abrasive blasting to Sa 2.5 standard (near-white metal).
  2. Sweep or vacuum all dust and debris. Allow 15–30 minutes surface settling.
  3. Wipe with solvent-dampened cloth (temperature > 15°C, humidity < 85%).
  4. Apply zinc-phosphate or iron oxide primer coat (if required by coating specification).
  5. Allow primer to cure for minimum time specified by product data sheet.

Aluminum Substrates

  1. Clean with mild alkaline solution; rinse with deionized water.
  2. Abrade with fine-grit abrasive (grit 120–180) to establish surface profile (Rz 2–4 µm).
  3. Remove all dust via vacuum and compressed air (oil-free).
  4. Wipe with solvent-dampened cloth within 4 hours of abrasion.
  5. Apply chromate or aluminum oxide primer (if required).
  6. Allow primer to cure per specification before coating application.

Composite Substrates

  1. Inspect for delamination or void damage. Repair via epoxy injection if necessary.
  2. Sand with medium-grit abrasive (grit 80–120) to dull surface finish and establish adhesion profile.
  3. Vacuum and wipe with damp cloth (avoid over-wetting; allow to dry completely).
  4. Apply primer designed for composite bonding per specification.
  5. Allow full cure before top-coat application.

Environmental Requirements

Temperature window: 10–30°C during preparation and application. Readings taken at substrate surface, not ambient air.

Humidity window: 35–85% relative humidity. If humidity exceeds 85%, defer work until conditions improve.

Dew point: Substrate temperature must exceed air dew point by minimum 3°C to prevent condensation.

Application Procedures

Application method and curing conditions directly affect coating performance. Procedures are type-specific. Coverage rates and cure times vary by ambient temperature.

Polymer-Based Coating Application

  1. Mix two-part system per specification (measure by volume or weight as indicated). Mix for 3–5 minutes until uniform.
  2. Let mixed material stand for 10–15 minutes (pot life varies; consult product data).
  3. Apply via spray or brush using even, overlapping passes (minimum 50% overlap on spray application).
  4. For spray: maintain tip distance 15–25 cm, spray angle perpendicular to surface.
  5. For brush: use natural or synthetic bristles; work in small sections to maintain wet edge.
  6. Apply in thin, even coats. Target total thickness 0.5–1.5 mm. Multiple thin coats preferred over single thick coat.
  7. Inter-coat interval: 4–8 hours at 20°C (temperature-dependent; check specification).
  8. Cure time before service: 7 days at 20°C minimum (reduced at elevated temperature).
  9. Coverage rate: approximately 8–12 m² per liter at 1.0 mm thickness (spray); 6–10 m² per liter (brush).

Mineral-Based Coating Application

  1. Shake or stir container thoroughly to resuspend ceramic particles (settlement occurs during storage).
  2. Transfer material to spray equipment reservoir (strain through fine mesh to remove agglomerated particles).
  3. Apply via spray only. Maintain tip distance 20–30 cm, spray angle perpendicular to surface.
  4. Spray in overlapping passes with 60–70% overlap. Single pass results in uneven coverage and poor adhesion.
  5. Target thickness 0.2–0.8 mm. Verify via wet-film gauge during application.
  6. Allow material to remain undisturbed for 24 hours before heat-curing step.
  7. Heat-cure per specification: typically 60–80°C for 4–8 hours (rate of temperature rise: maximum 5°C per minute).
  8. Cool to ambient temperature naturally before service.
  9. Coverage rate: approximately 4–6 m² per liter at 0.5 mm thickness.

Petroleum-Derived Coating Application

  1. For immersion method: submerge substrate in oil bath, maintain temperature 40–60°C, immerse for 15–30 minutes.
  2. For spray method: apply thin, uniform mist at 15–20 cm distance. Multiple light passes preferred.
  3. For brush method: apply thin, even coating; avoid pooling or runs.
  4. Allow excess material to drain or dry (2–4 hours at 20°C).
  5. Wipe excess from flat surfaces using lint-free cloth (retains thin protective layer).
  6. Cure time: 24 hours minimum at 20°C before service.
  7. Coverage rate: 15–25 m² per liter (varies by application method and material viscosity).
  8. No inter-coat interval required; reapplication can occur immediately if needed.
Durability and Reapplication

Coating service life depends on exposure environment and severity. Regular inspection enables early detection of degradation and planned maintenance.

Expected Service Life by Exposure Type

Coating Type Low Exposure (forest, protected) Moderate Exposure (plateau, some UV) High Exposure (coastal, alpine, desert)
Polymer-Based 4–6 years 3–4 years 2–3 years
Mineral-Based 6–8 years 5–6 years 3–4 years
Petroleum-Derived 2–3 years 1–2 years 6–12 months

Inspection Intervals

  • Low exposure environments: Annual inspection after first full year of service.
  • Moderate exposure environments: Bi-annual (every 6 months) after initial 3 months.
  • High exposure environments: Quarterly (every 3 months) after initial 6 weeks of service.

Increase inspection frequency if initial observations show accelerated degradation patterns.

Indicators of Coating Failure

  • Delamination: Coating separates from substrate, typically beginning at edges or damage zones. Substrate becomes exposed to corrosive environment.
  • Chalking: Surface develops fine, powder-like residue (oxidation of resin binders in polymer coatings). Indicates UV degradation.
  • Substrate exposure: Mechanical damage, impact, or abrasion breaches coating film and reveals substrate. Corrosion initiates at breach site.
  • Blistering: Coating bubbles and separates from substrate, typically caused by moisture vapor pressure beneath film.
  • Cracking: Visible splits in coating surface, result of adhesion loss, substrate movement, or thermal cycling.

Reapplication Decision Criteria

Recoat (topcoat application over existing coating) is acceptable when:

  • Coating adhesion is sound (no delamination). Test via cross-hatch adhesion test or impact.
  • Surface contamination is minimal and cleanable via light abrasion and solvent wipe.
  • Chalking or minor oxidation is present but substrate is not yet exposed.
  • Damage is localized to less than 20% of total surface area.

Full strip-and-recoat is required when:

  • Widespread delamination is present (greater than 20% of surface area).
  • Substrate exposure is extensive and corrosion has initiated.
  • Multiple coating layers have accumulated, creating adhesion risk between layers.
  • Coating type is changing (e.g., switching from polymer-based to mineral-based) and substrate requires different primer.

Reapplication Procedure

  1. Inspect and document existing coating condition via visual survey and testing.
  2. Clean existing surface via light abrasion (grit 120–180) to remove loose material and establish adhesion profile.
  3. Vacuum and solvent-wipe to remove all dust and contaminants.
  4. If prior coating is glossy, dull finish via light sanding to improve new coat adhesion.
  5. Apply new coat per application procedure for selected coating type (no separate primer required if existing coating is sound).
  6. Follow cure times per specification before service.
Revision

Coating performance data measured on platforms in continuous service across documented routes. Durability values reflect observed degradation rates under actual field conditions.