1. Introduction to Coal Tar Epoxy Technology
Coal tar epoxy coatings are two-component epoxy resin systems extended with pitch that provide a high-build, durable protective layer on concrete and steel surfaces. They are solvent-free or low-solvent, highly chemical resistant, and widely used in below-grade, marine, sewage, and aggressive environments.
Coal tar epoxy is most effective on isolated footings, pile caps, STPs, effluent tanks, and marine splash zones, where resistance to sulfates, sewage, and chemical attack is critical.
2. Advantages
- High build (≥ 300 μm DFT in 2 coats).
- Excellent chemical resistance (sewage, effluent, seawater, dilute acids & alkalis).
- Strong adhesion to concrete and steel (>1.5 MPa, concrete failure).
- Abrasion resistant (CS17 wheel, <20 mg/1000 cycles).
- Suitable for damp surfaces (after surface prep).
- Long service life when properly applied.
3. Limitations
- Not suitable for potable water or food contact areas.
- Requires thorough surface preparation (substrate defects visible through coating).
- Sensitive to application delays — recoat must be done within 12–24 hrs or surface must be abraded.
- Limited flexibility → not suited for dynamic cracking structures.
- Requires careful mixing (mechanical mixing mandatory).
4. Performance Table
Property | Requirement / Value | Test Standard |
Volume Solids | 80%+ | Manufacturer spec |
Mixed Density | ~1.65 kg/L | Datasheet |
Pot Life | 60 min @ 25°C | Manufacturer spec |
DFT | 300 μm (2 coats × 150 μm) | Datasheet |
Touch Dry | ~4 hrs @ 25°C | Manufacturer spec |
Final Cure | 5 days @ 25°C | Manufacturer spec |
Adhesion Strength | ≥ 1.5 MPa (concrete failure) | ASTM D4541 |
Abrasion Resistance | ≤ 20 mg/1000 cycles | ASTM D4060 |
Slant Shear Bond | > 10 MPa | ASTM C882 |
Resistance to Chemicals | Pass (sewage, effluent, seawater, dilute acids & alkalis) | ASTM C267 / MTS Test |
Weathering Resistance | No blistering, cracking, flaking | ASTM D4587 |
5. Recommended Use Cases
- Isolated footings with high groundwater table.
- Sewage treatment tanks, effluent drains, sumps.
- Marine splash zones (offshore piles, jetty supports).
- Below-grade concrete and steel in aggressive soils.
6. Application Steps (Standard Method Statement)
Surface Preparation
- Concrete: ≥ 28 days old, sound, free of laitance, grease, oil.
- Treat blowholes & pinholes with repair mortar.
- Substrate moisture < 5% preferred.
Mixing
- Mix components A & B with a slow-speed drill (300–400 rpm) for 3 minutes until uniform.
- Do not mix by hand.
Application
- Apply 2 coats (brush/roller/airless spray).
- Wet film thickness: 150 μm per coat → 300 μm total DFT.
- Second coat at right angle to first, after 4–6 hrs (30°C).
- If recoating delayed, abrade previous coat & solvent wipe.
Curing
- Touch dry: ~4 hrs at 25°C.
- Recoatable: 12 hrs.
- Final cure: 5 days.
Steel Surfaces
- Blast clean to SA 2½ (bright metal).
- Coat immediately after blasting.
7. Section Drawings
- Isolated footing cross-section with external coal tar epoxy coating.
- STP / sump tank wall detail.
8. Reference Standards
- ASTM D4541 – Adhesion (Pull-off Test).
- ASTM D4060 – Abrasion Resistance (Taber Test, CS17).
- ASTM C882 – Slant Shear Bond.
- ASTM C267 – Chemical Resistance.
- ASTM D4587 – Accelerated Weathering.
- IS 2645 – Waterproofing admixtures (if combined with integral).
9. Documents
Specifications, BOQ, and Checklist
5. Video Masterclass
SpecX Masterclass: Coal Tar Epoxy Coating — Coming Soon
Disclaimer
SpecX is an industry initiative & a neutral resource, compiled from industry references and best practices. It is not brand-specific. Always cross-check with project requirements and local codes before finalizing specifications.