About STP ShaliPoxy CTE 303

ShaliPoxy CTE 303 is STP Limited’s workhorse coal tar epoxy — a two-component system in which epoxy resin is blended with coal tar to produce a heavy-duty protective coating for steel and concrete that spends its life wet, buried or chemically attacked. What sets it apart from thinner-film competitors is build: applied wet-on-wet at the recommended 350-420 micron wet film, it dries down to 300 ± 30 microns in a single coat, so a typical 600 micron immersion-grade system needs only two coats instead of three or four. It carries AWWA C-210:2015 and SSPC Paint 16 compliance, the two specifications most Indian consultants call up for coal tar epoxy on water and pipeline infrastructure.

For contractors, the practical appeal is that it applies direct to metal — blast-clean the steel, coat the same shift, and skip the primer line item (though STP recommends ShaliPrime CT or ShaliPrime Zn Ph 60 where a primer is specified). The cured film is unusually forgiving for an epoxy: over 30% elongation and a Shore A hardness of 75 mean it flexes with thermal movement rather than cracking, while pull-off adhesion of 6-8 MPa on steel keeps it anchored. Each 20 L kit ships as 15 L of Component A and 5 L of Component B with a 12-month shelf life. Space Arc Engineering supplies ShaliPoxy CTE 303 across Delhi NCR and pan-India, with applicator support for tank, pipeline and marine jobs.

The technical insight

Coal tar epoxies work because the two ingredients cover each other’s weaknesses. Coal tar is intensely hydrophobic — one of the lowest water-vapour-transmission binders available — but on its own it is soft and thermoplastic. Epoxy resin brings crosslinked toughness, adhesion and chemical resistance, but straight epoxies are brittle and comparatively permeable in permanent immersion. Blended, the tar phase plasticises the epoxy matrix and fills it with a moisture-blocking barrier: that is why CTE 303 survives 30-day immersion in deionised water, 1% sulphuric acid and 1% caustic soda with no blistering or disbonding, and passes 500 hours of salt spray at 300 microns. The 75 ± 3% volume solids explain the high build — most of what you apply stays on the wall instead of evaporating. And with dielectric strength above 250 V/mil and cathodic disbondment under 10 mm at 30 days (AWWA C-210), the film behaves as an electrical insulator that will not creep back from holidays, which is exactly what a buried pipeline under impressed-current cathodic protection needs.

Where it is used

• External coating of crude oil storage tanks and underground steel structures
• Buried pipelines and steel under cathodic protection, including sewage rising mains
• Penstocks, barrage gates and dam hydro-mechanical steelwork (non-potable service)
• Splash and tidal zone steel in docks, jetties and harbours
• Sewage and effluent treatment plant tanks, channels and digesters
• Foundation walls, basements and sumps in continuous ground-water contact
• Internal lining of tanks holding sea water, effluent or crude oil (not potable water)
• Concrete surfaces exposed to dilute acids, alkalis and salt-laden environments

Key advantages

• Very high build — 300 ± 30 microns DFT per coat, so a 600 micron system finishes in two coats
• Direct-to-metal application on blast-cleaned steel; no separate primer required
• Flexible cured film (elongation above 30%) absorbs thermal shock and impact without cracking
• Proven immersion resistance to sea water, crude oil, 1% H2SO4 and 1% NaOH per AWWA C-210 testing
• Compatible with cathodic protection — dielectric strength over 250 V/mil, cathodic disbondment under 10 mm
• Complies with AWWA C-210:2015 and SSPC Paint 16, easing consultant approvals
• Applies by brush, roller or airless spray with a workable 3-4 hour pot life
• Strong mechanical performance: 6-8 MPa adhesion on steel and abrasion loss of only 115 ± 10 mg (1000 cycles, CS-17)

Limitations & considerations

• Not suitable for surfaces in contact with potable water or foodstuffs — specify a taste-and-odour-approved epoxy for drinking water tanks
• Available only in black, and like all epoxies it chalks on prolonged sunlight exposure (cosmetic, not protective, degradation)
• Contains coal tar and is flammable — full PPE, forced ventilation in confined spaces and ignition control are mandatory
• Application window is strict: 10-40°C substrate and ambient, relative humidity below 80%, substrate moisture under 5% and 3°C above dew point
• If the recoat is delayed beyond 16 hours, the first coat must be abraded and solvent-wiped to restore intercoat adhesion
• Full cure before immersion service takes 7 days at 30°C, stretching to 15 days at 10°C

Selection & best practice

Specifications

Industry use cases

How we position STP ShaliPoxy CTE 303

Within the STP family, CTE 303 is the high-build pick of the ShaliPoxy CTE range — choose ShaliPoxy CTE 103 or CTE 203 where the specification calls for conventional thinner-film coal tar epoxy, and ShaliPoxy CTE 303 MI when you must coat damp or green-blasted substrates. Pair it with ShaliPrime Zn Ph 60 zinc phosphate primer on critical steel and keep STP Thinner on site for viscosity adjustment and tool cleaning. If the tender specifies Fosroc, we stock Nitocote ET402, a coal-tar-extended 100% solids epoxy covering similar seawater and effluent duties. And where black coal tar chemistry is ruled out — visible areas or potable water tanks — talk to us about tar-free epoxy alternatives from the Fosroc Nitocote and Sika ranges.

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