Marine Coating Im2 — Choosing epoxy mastic vs chlorinated rubber vs coal tar for Thai offshore work

What Is ISO 12944 Im2

ISO 12944-2 divides corrosion environments into:

• C1-C5 — atmospheric (rural, urban, industrial, coastal, offshore)
• CX — extreme (offshore beyond C5)
• Im1 — fresh water immersion
• Im2 — sea water + sea water splash zone
• Im3 — soil immersion (buried)

Im2 = the most frequently required class in Thai marine projects — ship hull above + below waterline, dock pile, offshore platform splash zone, sea water intake structure, jetty + pier.

3 Main Coating Systems

1. Chlorinated Rubber (CR)

Spec:

• Single-pack, solvent-borne
• DFT 75-200μm/coat (typically 3-4 coats total)
• Cure: solvent evaporation 6-24 hr
• Operating temp: -20°C to 70°C

Sweet spot: ship hull above water, splash zone topcoat, refurbishment.

Advantages:

• Cures at low temperatures — suitable for winter / cold ambient
• Good salt spray resistance
• Recoatable for up to 6 months without sanding
• Single-pack — minimum waste

Limitations:

• Low DFT per coat — requires many coats
• No immersion beyond the splash zone (Im2 max)
• Solvent-borne — high VOC

2. Coal Tar Epoxy (CTE)

Spec:

• 2K (amine/polyamide cure)
• DFT 200-500μm/coat
• Operating temp: -20°C to 95°C
• Volume solids 55-75%

Sweet spot: buried pipe, storage tank lining, sewer manhole, dock pile underwater.

Advantages:

• Best barrier protection in the group
• High DFT/coat → fewer coats → faster project
• Withstands immersion Im2 + Im3

Limitations:

• EU classified CTPV = carcinogen Cat 1B under REACH — banned for EU consumers in 2010
• Thailand: DIW Annex II lists CTPV as a controlled substance but phase-out is not yet complete
• No UV exposure (chalk + crack)
• The market is shifting to 2K epoxy mastic as a replacement

3. 2K Epoxy Mastic (Modern Replacement)

Spec:

• 2K bisphenol-A epoxy + amine cure
• DFT 150-400μm/coat
• Operating temp: -20°C to 120°C
• Volume solids 75-90% (high-solids low-VOC)

Sweet spot: modern replacement for every Im2 + Im3 application that previously used CTE.

Brand: Hempel Hempadur Mastic 4588, Jotun Jotamastic 90, Sigma SigmaShield 880, International Intershield 300.

Advantages:

• Safe — no carcinogen issue
• Low VOC — aligns with the Thai DIW phase-out roadmap
• High DFT/coat + fast cure
• Cost competitive — within 10-20% of CTE

Decision Matrix

graph TD
    Start[Marine project Im2] --> Q1{Application area?}
    Q1 -->|Above splash zone
UV exposed| CR[Chlorinated Rubber + epoxy primer
4 coats × 100μm = 400μm DFT]
    Q1 -->|Splash zone immerse| Q2{TOR specifies CTE?}
    Q1 -->|Permanent immersion| Q3{TOR cert?}
    Q2 -->|Yes| CTE[Coal Tar Epoxy
2 coats × 400μm = 800μm DFT]
    Q2 -->|No| Mastic1[2K Epoxy Mastic
2 coats × 300μm = 600μm DFT]
    Q3 -->|NORSOK M-501| Mastic2[Hempadur Mastic 4588
3 coats × 250μm = 750μm DFT]
    Q3 -->|Generic| Mastic3[Jotamastic 90 / SigmaShield
2 coats × 300μm + topcoat]
    style Mastic1 fill:#10b981,color:#fff
    style Mastic2 fill:#10b981,color:#fff
    style Mastic3 fill:#10b981,color:#fff
    style CR fill:#3b82f6,color:#fff
    style CTE fill:#f97316,color:#fff

Surface Preparation — Critical for Im2

SSPC-SP10 (near-white blast) mandatory for every system:

• Abrasive size 35-100μm Sa 2.5
• Salt contamination test ISO 8502-9: ≤ 50 mg/m²
• Humidity ≤ 85%
• Substrate temp 3°C above dew point
• Recoat window 4 hours max

Do not:

• Use hand tool prep (SSPC-SP2) for Im2
• Apply during rain or humidity > 85%
• Apply over flash rust > 1 hour old

QC + Inspection

• WFT (wet film thickness) per ASTM D4414 — at application
• DFT (dry film thickness) per ASTM D7091 (magnetic) — after cure
• Holiday test per ASTM D5162 — wet sponge low-voltage
• Adhesion per ASTM D4541 — pull-off ≥ 3 MPa for Im2

Inspector cert: a NACE Level 2 or ICorr Painting Inspector Level 2 must be on site during application + sign off the report.

Further Comparison

See the more detailed tables:

• /compare/chlorinated-rubber-vs-coal-tar-vs-bitumen-marine-coating — compare binder type
• /compare/iso-12944-c3-vs-c4-vs-c5-coating-selector — atmospheric class
• /compare/zinc-rich-vs-epoxy-vs-pu-coating — primer selection

Or calculate 20-year TCO at /tools/paint-tco-calculator.

Saha Service

Saha supplies + supervises marine coating across every system:

• Material: Hempel / Jotun / Sigma / International / TOA — every Im class
• Application contractor: SSPC-QP1 + ICorr Level 2 painter
• Surface prep: SSPC-SP10 abrasive blast + salt test
• QC: WFT + DFT + holiday test + adhesion + report
• Documentation: photo of every step + sign-off + 10-year warranty (with Hempel/Jotun spec)

Send your substrate spec + area + Im class + cert requirement → system recommendation + quotation within 48 hr.