STP ShaliPoxy CTE 103 MI
Two-component moisture-insensitive coal tar epoxy that cures on damp concrete and moist steel — anti-corrosive protection without waiting for the substrate to dry.
What is it?
A 2K moisture-insensitive coal tar epoxy coating from STP Limited, built on a special hardener system that cures over damp (green) concrete and moist metal, even above 85% RH.
Where is it used?
Sewage treatment plants, below-grade concrete, MS and concrete pipelines, sumps and metallic structures where the surface cannot be dried before coating.
Why use it?
It removes the dry-substrate wait: 2.5 MPa pull-off on green concrete, 6.0 MPa on moist steel, 2,000-hour salt-spray endurance and 30-day dilute acid/alkali immersion resistance.
How is it applied?
Brush, roller or airless spray at 150–180 micron DFT per coat and 4–4.5 m²/L; mix 3:1 by volume, allow a 20-minute induction, overcoat after 10–12 hours at 30°C.
About STP ShaliPoxy CTE 103 MI
ShaliPoxy CTE 103 MI is STP Limited’s moisture-insensitive grade of coal tar epoxy — a two-component, liquid epoxy resin coating whose hardener keeps curing even when the substrate is damp. Where a conventional coal tar epoxy demands substrate moisture below 5%, this grade bonds to green concrete, moist mild steel and surfaces sitting above 85% relative humidity, tolerating substrate moisture up to 15%. It films out black at 150–180 microns per coat from 75% volume solids, and the cured coating carries the chemical, corrosion and abrasion resistance the CTE family is known for.
For contractors in Delhi NCR and across India, the practical value is programme time. Below-grade retaining walls, sewage treatment structures and pipeline trenches rarely dry out on schedule, and monsoon humidity alone can stall a standard epoxy for days. CTE 103 MI removes that dependency: prepare the surface, take off free water, and coat the same day. Space Arc Engineering supplies it in STP’s 20 L combo packs with TDS-backed documentation and applicator support for immersion-grade and below-grade protection work.
The technical insight
The “MI” is a hardener story. A standard amine-cured epoxy competes with water at the substrate interface — moisture blushes the film, starves adhesion and leaves pinholes. CTE 103 MI pairs epoxy resin with a specially selected hardener and additive package whose cure reaction proceeds preferentially on damp surfaces, so the low-viscosity mix penetrates wet concrete pores and displaces water rather than trapping it. Coal tar then does the second half of the job, plasticising the epoxy matrix into a flexible, strongly hydrophobic film with very low water transport. The test data bears this out: water absorption under 0.5% (ASTM D 570), coating resistance holding at 10⁹ ohm·cm² over six months, 2,000 hours of salt spray at 150 microns (ASTM B 117) and 30-day immersion in deionised water, 1% H2SO4 and 1% NaOH with no blistering or debonding. Adhesion tells the same story from the substrate side — 2.5 MPa pull-off on green concrete, near the cohesive limit of young concrete itself, and 6.0 MPa on moist steel.
Where it is used
- Coating damp and green concrete in basements, foundation walls and sumps
- Concrete and steel structures in sewage and effluent treatment plants
- External protection of MS and concrete pipelines and metallic structures
- Concrete surfaces at over 85% RH with substrate moisture up to 15%
- Monsoon-season and shutdown maintenance where substrate drying is impractical
- Below-grade and below-water-table structures needing anti-corrosive protection
- Rehabilitation of wet wells, drains and non-potable water-retaining structures
Key advantages
- Cures and bonds over damp concrete and moist steel — no forced drying cycle
- Handles ambient humidity above 85% RH and substrate moisture up to 15%
- Pull-off adhesion of 2.5 MPa on green concrete and 6.0 MPa on moist steel
- 75% volume solids builds 150–180 micron DFT in a single coat
- Passes 2,000-hour salt spray at 150 microns and ISO 20340 cyclic corrosion
- 30-day immersion in water, 1% acid and 1% alkali without blistering or debonding
- Low-viscosity mix penetrates damp concrete pores for a keyed, sealed interface
- Applies by brush, roller or airless spray with a workable 4-hour pot life
Limitations & considerations
- Black only — coal tar chemistry offers no colour options and chalks under prolonged sunlight
- Not suitable for potable water or foodstuff contact, in line with the rest of the coal tar epoxy range
- Tolerates dampness, not free water — ponded or running water must be removed before coating
- Requires a 20-minute induction period after mixing, which slows batching on fast-moving crews
- Ambient application window is 10–50°C, and full cure takes 7 days at 30°C
- Coal tar content demands strict PPE, ventilation and skin-contact discipline on site
Selection & best practice
Wire-brush or grit-blast to remove laitance, rust flakes, algae and unsound material — sand blasting for steel — then vacuum or wash down and let free water drain; damp is acceptable, ponded water is not. Pre-stir each drum at around 400 rpm, combine the full pre-weighed packs at 3:1 by volume and mix for five minutes with the paddle kept below the surface to avoid entraining air. Give the mix its 20-minute induction time, restir briefly, then apply by brush, roller or airless spray (23 thou tip minimum, 2,200–2,400 psi) at 200–250 microns wet to yield 150–180 microns dry. At 30°C expect touch dry in 3–4 hours and overcoat at 10–12 hours; plan two coats for immersion or below-grade duty and confirm DFT with a gauge rather than coverage arithmetic alone. Work within the 4-hour pot life and clean tools immediately with STP Thinner.
Specifications
| Form and colour | Two-component coal tar epoxy coating; black |
| Mixing ratio (by volume) | 3 : 1 (Component A : Component B) |
| Volume solids | 75 ± 5% (ASTM D 2697 basis) |
| Theoretical coverage | 4–4.5 m²/L per coat, surface dependent |
| Film thickness per coat | 150–180 micron DFT (200–250 micron WFT) |
| Pot life (ASTM D 2471) | 4 hours (100 g sample, 30°C) |
| Drying at 30°C | Touch dry 3 h; overcoat 10–12 h; hard dry 24 h; full cure 7 days |
| Adhesion pull-off (ASTM D 4541) | 2.5 ± 0.5 MPa on green concrete; 6.0 ± 0.6 MPa on moist steel |
| Packing and shelf life | 20 L combo pack; 12 months unopened at 5–38°C |
Industry use cases
Water & Wastewater
STP and ETP civil works stay damp by nature. CTE 103 MI coats clarifier walls, wet wells and channels without waiting for a dry window, and resists the dilute acid and alkali exposure its 30-day immersion tests replicate.
Pipelines & Metallic Structures
External anti-corrosive duty on MS pipeline sections and steel structures recoated in the field, where blast-cleaned steel flash-rusts and turns moist faster than a conventional epoxy can go on.
Below-Grade Infrastructure
Foundation walls, basements and sumps sitting below the water table, where substrate moisture never drops to the roughly 5% a moisture-sensitive coating needs.
Industrial Maintenance
Shutdown-window recoating of tanks, drains and plant structures during monsoon months, when ambient RH above 85% rules out standard epoxy systems altogether.
Ports & Wet Utilities
Intermittently wet concrete and steel in pump houses, drains and water-side utility structures that need a flexible, abrasion-resistant protective film.
Frequently asked questions
Can ShaliPoxy CTE 103 MI be applied on a wet surface?
How is the MI grade different from standard ShaliPoxy CTE 103?
What coverage should I budget?
How many coats are needed?
Is it safe for drinking water tanks?
What pack size does it come in, and how long does it keep?
How we position STP ShaliPoxy CTE 103 MI
Within the STP range, CTE 103 MI is the wet-surface specialist. When the substrate can be blast-cleaned and dried, standard ShaliPoxy CTE 103 — with AWWA C-210 and SSPC Paint 16 compliance — is the more economical pick for pipelines and tank externals, primed where needed with ShaliPrime CT or ShaliPrime Zn Ph 60. For projects specified on Fosroc, Nitocote ET402 covers the solvent-free coal tar epoxy duty, while Nitocote EP405 is the damp-tolerant, tar-free choice where coal tar is excluded. Space Arc stocks all of these and will match the grade to the substrate condition, not the other way around.
Fosroc Nitocote ET402 — Specifiers choose Nitocote ET402 when the substrate can be properly dried and the project is written around a solvent-free Fosroc coal tar epoxy; CTE 103 MI remains the answer when the surface will not dry.
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