STP ShaliPoxy CTE 203
Two-component, high-build coal tar epoxy that lays down 200-250 microns on steel or concrete in a single wet-on-wet coat — direct to metal, no primer required, and fully compatible with cathodic protection.
What is it?
A 2K flexible coal tar epoxy protective coating from STP Limited, formulated for high film build — 200-250 microns dry film in one wet-on-wet coat — on mild steel and concrete, conforming to AWWA C-210: 2015 and SSPC Paint 16.
Where is it used?
Buried and submerged steel — pipelines, penstocks, barrage gates, sheet piling — plus crude oil tank exteriors, sewage treatment structures, sumps and foundation walls across water, oil and gas, and industrial projects.
Why use it?
One coat replaces the usual two or three, it goes direct to metal without a primer, and it holds up under continuous immersion, 1,000-hour salt spray and impressed-current cathodic protection with less than 10 mm disbondment.
How is it applied?
Mix the pre-weighed components 3:1 by volume, then apply by brush, roller or airless spray at roughly 3.5 m²/L per coat. Touch dry in 4 hours at 30°C; recoat between 8 and 30 hours; full cure in 7 days.
About STP ShaliPoxy CTE 203
ShaliPoxy CTE 203 is STP Limited’s workhorse coal tar epoxy for steel and concrete that spends its life buried, submerged or splashed. Two pre-weighed components mix 3:1 by volume into a black, semi-gloss coating with 70% volume solids, which is what lets it build 200-250 microns of dry film in a single wet-on-wet application — a thickness most conventional epoxies need two or three coats to reach. The cured film is deliberately flexible, with 15-20% elongation, so it rides out thermal movement, impact and handling knocks that would crack a rigid coating. It conforms to AWWA C-210: 2015, SSPC Paint 16 and Corps of Engineers C200/C200a.
On site, its biggest practical advantage is direct-to-metal application: on a properly blast-cleaned surface no primer is needed, though ShaliPrime CT or ShaliPrime Zn Ph 60 can be used where a specification calls for one. The film tolerates continuous service at 95°C and occasional excursions to 120°C, resists sea water, crude oil, dilute acids and alkalis, and survived 30-day immersion in demineralised water, 1% sulphuric acid and 1% caustic soda without blistering or disbonding. Space Arc Engineering supplies ShaliPoxy CTE 203 in 20 L combo packs across Delhi NCR and Pan-India, with applicator crews for pipeline, hydro and plant coating packages.
The technical insight
Coal tar epoxy works because the two ingredients cover each other’s weaknesses. Coal tar pitch is one of the most water-impermeable, biologically inert binders available — but on its own it is soft and creeps. Epoxy resin brings hard adhesion (8 ± 0.5 MPa pull-off here) and chemical resistance — but pure epoxies are moisture-sensitive and brittle in thick films. Blended, the pitch plasticises the epoxy network into a dense, hydrophobic barrier that water and dissolved salts struggle to cross, which is why the film posts a dielectric strength above 250 V/mil and cathodic disbondment under 10 mm after 30 days. That dielectric quality matters on CP-protected pipelines: the coating does the primary barrier work, so the impressed current only has to protect pinholes and holidays instead of bare steel, keeping current demand low. The mineral-filled, high-solids formulation is also thixotropic enough to hang 300 microns wet on vertical steel without sagging — the mechanism behind the single-coat build.
Where it is used
- Internal and external coating of MS and concrete pipelines
- Crude oil storage tanks and buried steel structures
- Penstocks, dam and barrage gates in hydro and irrigation projects
- Sheet piling and pipe piling in marine and riverfront works
- Concrete and steel surfaces in sewage and effluent treatment plants
- Foundation walls, sumps and other below-grade substructures
- Structural steel and process areas in paper mills and chemical plants
- Buried pipelines operating under controlled cathodic protection
Key advantages
- 200-250 micron DFT in one wet-on-wet coat — fewer passes, fewer site mobilisations than 2-3 coat systems
- Direct-to-metal application on blast-cleaned steel; primer optional, not mandatory
- Cathodic protection compatible, with disbondment under 10 mm in the 30-day AWWA C 210 test
- Rated excellent after 1,000 hours salt spray at 300 microns DFT (ASTM B 117)
- Flexible film with 15-20% elongation absorbs impact, abrasion and thermal shock
- No blistering or peeling after 30-day immersion in demineralised water, 1% H2SO4 and 1% NaOH
- Handles 95°C continuous and 120°C occasional service temperatures
- Resists sea water, crude oil, minerals, dilute acids and alkalis in long-term contact
Limitations & considerations
- Available in black semi-gloss only — it cannot be tinted, so it is unsuitable where a decorative or light-coloured finish is specified
- Solvent-based with a flash point above 30°C: tank internals and confined spaces need forced ventilation and flameproof equipment
- The recoat window closes at 30 hours (30°C); an overcoat after that requires abrading the surface to restore intercoat adhesion
- Application is restricted to 10-49°C, and new concrete must be at least 28 days old before coating
- Combo packs are pre-weighed for full 3:1 mixing — part-mixing is not practical, and the 4-hour pot life forces disciplined batch sizing
- The datasheet carries no potable-water certification, so do not specify it for drinking-water contact without written confirmation from STP
Selection & best practice
Surface preparation decides how long this coating lasts. Blast-clean steel or grind mechanically, then remove every trace of dust, oil, grease and loose scale with compressed air or wire brushing; on concrete, wait until the substrate is at least 28 days old. Check that ambient, surface and material temperatures all sit within the 10-49°C application band. Stir each component separately with a slow-speed stirrer, then combine the full pre-weighed A and B packs and mix for 5 minutes, keeping the spiral blade submerged to avoid dragging in air. Let the mix stand 5 minutes to release entrapped air, restir gently, and use it within the 4-hour pot life. Apply by brush, roller or airless spray — tip size 0.48-0.88 mm at 3,500-4,500 psi — targeting about 300 microns wet film per coat. Allow 4 hours to touch dry before a wet-on-wet second pass, and keep any recoat inside the 8-30 hour window at 30°C. Hold off immersion or chemical service until full cure: 7 days at 30°C, 15 days at 10°C. Clean tools immediately with STP Thinner.
Specifications
| Standards compliance | AWWA C-210: 2015, SSPC Paint 16, Corps of Engineers C200/C200a |
| Mixing ratio | 3 : 1 by volume (pre-weighed 2K combo pack) |
| Solids content | 70 ± 2% by volume |
| Dry film thickness | 200-250 microns per coat, wet-on-wet (approx. 300 microns WFT) |
| Theoretical coverage | 3.5 m²/L per coat at 200 micron DFT |
| Pot life | 4 hours (100 g sample, ASTM D 2471) |
| Adhesion, pull-off | 8 ± 0.5 MPa at 7 days (ASTM D 4541) |
| Curing at 30°C | Touch dry 4 h; recoat 8-30 h; full cure 7 days |
| Packing and shelf life | 20 L combo pack; 12 months sealed at 5-38°C |
Industry use cases
Hydro & Irrigation
Penstocks, barrage gates and dam radial gates take constant immersion plus abrasion from silt-laden water; the flexible, abrasion-resistant film protects gate steel through wet-dry cycling and operation.
Oil & Gas
Buried MS pipelines and crude oil tank externals under cathodic protection — low current demand from the high dielectric film and under-10 mm cathodic disbondment keep CP systems efficient.
Sewage & Effluent Treatment
Clarifiers, digesters, MS piping and concrete tanks at STPs and ETPs face dilute acids, alkalis and microbial attack; the coating passes ASTM G 21 resistance to micro-organisms.
Marine & River Works
Sheet and pipe piling at jetties and riverfront structures sit in the splash and immersion zones where salt water is harshest — 1,000-hour salt spray performance covers exactly this exposure.
Industrial Plants
Paper mills and chemical plants use it on sumps, foundation walls and structural steel where spillage, fumes and washdown chemicals corrode uncoated surfaces.
Frequently asked questions
Does ShaliPoxy CTE 203 need a primer?
What coverage should I budget per 20 L pack?
How long before the coating can go into immersion service?
Is it suitable for pipelines under cathodic protection?
What if I miss the recoat window between coats?
Can it be used inside drinking-water tanks?
How we position STP ShaliPoxy CTE 203
Within the STP family, ShaliPoxy CTE 203 is the high-build grade: where the specification calls for a lighter 135-165 micron system, ShaliPoxy CTE 103 is the economical sibling, and ShaliPrime CT or ShaliPrime Zn Ph 60 slot in underneath when a primer coat is mandated. Pair it with STP Thinner for tool cleaning and viscosity adjustment. For projects standardised on Fosroc, Nitocote ET550 is the closest pitch-extended epoxy equivalent, while potable-water tank linings should move to a certified solvent-free epoxy rather than any coal tar system. Space Arc can quote supply-only or supply-and-apply for all of these.
Fosroc Nitocote ET550 — Specifiers who want a heavier single-spray film — Nitocote ET550 builds a minimum 350 microns in one airless pass — or whose project is standardised on Fosroc for sewage tank linings and dock steel often choose it over CTE 203.
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