STP ShaliPoxy CTE 103
A two-component, flexible coal tar epoxy that goes direct to metal and keeps buried and immersed steel and concrete protected — tested to AWWA C-210:2015 and SSPC Paint 16.
What is it?
A two-component epoxy resin coating modified with coal tar (Component A : B mixed 3:1 by volume), producing a black, flexible, anti-corrosive barrier film for steel and concrete.
Where is it used?
Buried pipelines, crude oil tank bottoms and underground structures, dams, barrage gates, penstocks, sewage treatment plants, sumps, foundation walls and splash zones in docks and harbours.
Why use it?
It applies direct to metal without a primer, tolerates continuous immersion and burial, stays flexible (20-25% elongation) and is compatible with cathodic protection systems.
How is it applied?
Brush, roller or airless spray over Sa 2½ blast-cleaned steel or 28-day-old concrete, at 150-200 micron wet film per coat; recoat after 4-7 hours at 30°C.
About STP ShaliPoxy CTE 103
ShaliPoxy CTE 103 from STP Limited is the workhorse of the coal tar epoxy family: a two-pack, cold-cured coating in which the epoxy binder is extended with coal tar to build a dense, water-shedding black film on steel and concrete. It is formulated for direct-to-metal application, so on a freshly blasted pipeline or penstock you can start coating without waiting for a separate primer — though STP’s ShaliPrime CT or ShaliPrime Zn Ph 60 can be used underneath where a specification demands it. The product carries AWWA C-210:2015 and SSPC Paint 16 compliance, the two benchmarks Indian consultants most often cite for buried and immersed pipeline coatings.
Each 20-litre pack (15 L Component A, 5 L Component B) covers roughly 5 m² per litre per coat at 125 ± 10 micron DFT, and the cured film has been through the tests that matter for below-grade service: 500-hour salt spray, 30-day immersion in dilute acid and alkali, QUV weathering and cathodic disbondment under 10 mm. One honest caveat up front — STP does not recommend it for potable water or foodstuff contact, so treat it as an industrial and wastewater coating, not a drinking-water lining.
The technical insight
Why does adding coal tar to an epoxy make it better underground? Straight epoxies cure into hard, tightly cross-linked films — excellent adhesion, but relatively brittle and still measurably permeable to water over years of immersion. Coal tar pitch is intensely hydrophobic; blended into the epoxy matrix it plugs the diffusion paths water vapour and chloride ions would otherwise follow, while also plasticising the film. That is where CTE 103’s 20-25% elongation and 1/8-inch mandrel flexibility come from — the coating flexes with pipe settlement and thermal shock instead of cracking. The film’s dielectric strength of 250-260 V/mil matters too: on cathodically protected pipelines the coating must electrically isolate the steel without disbonding around holidays, and CTE 103’s sub-10 mm cathodic disbondment result shows it holds its grip under impressed current. Adhesion of 4-6 MPa pull-off on blasted steel completes the system.
Where it is used
- External coating of buried and underground steel pipelines, including lines under cathodic protection
- Crude oil storage tank exteriors, bottoms and associated underground structures
- Dams, barrage gates and penstocks in hydro and irrigation projects (non-potable service)
- Sewage and effluent treatment plant structures — clarifiers, channels, digesters
- Foundation walls, sumps and below-grade concrete in industrial plants
- Splash-zone protection of steel and concrete in docks, jetties and harbours
- Marine and coastal structural steel exposed to salt-laden atmospheres
- Concrete surfaces in continuous contact with raw water, seawater or effluent
Key advantages
- Direct-to-metal application on blasted steel — no separate primer needed, saving a full application cycle
- Complies with AWWA C-210:2015 and SSPC Paint 16, easing approval on pipeline and water-infrastructure specs
- Flexible film with 20-25% elongation absorbs settlement, vibration and thermal shock without cracking
- Compatible with cathodic protection: dielectric strength 250-260 V/mil, cathodic disbondment under 10 mm in 30 days
- Proven immersion resistance — 30 days in demineralised water, 1% H2SO4 and 1% NaOH with no blistering or peeling
- Passes 500-hour salt spray at 100 micron DFT plus resistance to micro-organisms (ASTM G 21), suiting sewage and marine duty
- Low-viscosity mix applies easily by brush, roller or airless spray with 150-200 micron wet film per coat
- Tough surface: scratch resistance up to 2 kg load and only 110 ± 10 mg abrasion loss over 1,000 Taber cycles
Limitations & considerations
- Not recommended for surfaces in contact with potable water or foodstuffs — specify a potable-certified epoxy lining instead
- Contains coal tar: full PPE, good ventilation and controlled handling are mandatory, and it is available in black only
- Chalks on prolonged sunlight exposure, as all epoxies do — cosmetic rather than protective loss, but visible on exposed structures
- Tight overcoating discipline: recoat within 4-7 hours at 30°C; beyond 16 hours the previous coat must be abraded and solvent-wiped
- Application window is 10-40°C with substrate moisture below 5% and RH under 80% — cold, damp or rainy conditions risk incomplete cure
- Pot life of 3.5-4 hours means mixed material must be planned around crew output, not left standing
Selection & best practice
Surface preparation decides how long this coating lasts. Blast steel to ISO Sa 2½ and coat the same shift, before flash rusting starts; new concrete must be at least 28 days old and blown clean of dust. Check that the substrate is at least 3°C above dew point and RH is below 80% before you open the packs. Stir each component separately, then combine A and B at 3:1 by volume and machine-mix for 3-5 minutes with a slow-speed stirrer, keeping the paddle submerged — never mix by hand, and never thin the material. Lay down 150-200 microns wet film per coat by brush, roller or airless spray (60:1 pump, 0.58-0.88 mm tip, 210-250 kg/cm² tip pressure). At 30°C the film is touch dry in about 4 hours; apply the second coat between 4 and 7 hours, and if the window stretches past 16 hours, abrade and solvent-wipe first. Clean tools immediately with STP Thinner.
Specifications
| Mixing ratio (Comp A : Comp B) | 3 : 1 by volume |
| Theoretical coverage | 5 m²/L per coat at 125 ± 10 micron DFT |
| Recommended wet film thickness | 150-200 microns per coat (ASTM D 4414) |
| Volume solids | 65 ± 5% (ASTM D 2697) |
| Pot life (100 g at 28°C) | 3.5-4 hours (ASTM D 2471) |
| Adhesion, pull-off on steel | 4-6 MPa (ASTM D 4541) |
| Elongation | 20-25% (ASTM D 638) |
| Curing at 30°C | Touch dry 4 h; recoat 8-30 h; full cure 7 days |
| Packaging / shelf life | 20 L pack (15 L A + 5 L B); 12 months at 5-38°C |
Industry use cases
Oil & Gas
External protection of buried crude and product pipelines and tank-farm structures, where CP compatibility and cathodic disbondment below 10 mm keep the coating and impressed-current system working together.
Water Resources & Hydro
Barrage gates, penstocks and dam appurtenances in irrigation and hydro schemes — continuous raw-water immersion with abrasion from silt-laden flow, in non-potable service.
Sewage & Effluent Treatment
Clarifier internals, channels and digester surfaces at STPs and CETPs, where resistance to dilute acids, alkalis and microbial attack (ASTM G 21) is routinely specified.
Ports & Marine
Splash-zone coating of jetty piles, fenders and quay structures facing salt spray and tidal wet-dry cycling, backed by 500-hour salt-spray performance.
Industrial & Infrastructure
Foundation walls, sumps and below-grade concrete in process plants and basements where groundwater contact demands a continuous, flexible barrier film.
Frequently asked questions
Can ShaliPoxy CTE 103 be used inside drinking water tanks or pipelines?
Do I need a primer before applying it on steel?
How much material do I need for a two-coat system?
Is it suitable for pipelines under cathodic protection?
What is the recoat window between coats?
How is CTE 103 different from the higher grades like CTE 303?
How we position STP ShaliPoxy CTE 103
Within the STP family, ShaliPoxy CTE 103 pairs naturally with ShaliPrime CT or ShaliPrime Zn Ph 60 where a primer is specified, STP Thinner for tool cleaning, and the higher-build ShaliPoxy CTE grades (such as CTE 303) when a spec calls for thicker films in fewer coats. Specifiers comparing coal tar epoxies should also look at Fosroc Nitocote ET402 from our Fosroc range — a solvent-free, 100% solids coal-tar-extended epoxy that suits concrete in sewage and seawater contact. And if the asset holds drinking water, neither product applies: talk to Space Arc about potable-certified epoxy linings before you finalise the specification.
Fosroc Nitocote ET402 — Specifiers often choose Nitocote ET402 when they want a solvent-free, 100% solids coal-tar epoxy for concrete in sewage or seawater service, trading CTE 103’s low-viscosity spray convenience for higher build and lower solvent emission per coat.
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