STP ShaliPrime CT
Two-component coal tar epoxy primer that soaks into concrete and grips steel, giving coal tar coatings, membranes and damp-proof plaster a sealed, well-bonded base at 8–10 m²/L.
What is it?
A two-component coal tar epoxy primer from STP Limited for concrete and metal surfaces, supplied in 20 L drums.
Where is it used?
Under coal tar epoxy coatings, waterproofing membranes and basement plaster — sewage treatment plants, substructures, marine and industrial floors.
Why use it?
Its low-viscosity mix penetrates porous concrete, seals air-release paths that cause pinholes, and cures to a damp-checking, root-resistant film with nil water absorption.
How is it applied?
Mix the two packs for 3 minutes with a slow-speed drill, then brush, roller or spray a thin continuous film; overcoat after 6–8 hours of drying.
About STP ShaliPrime CT
ShaliPrime CT sits at the start of STP Limited’s coal tar system: it is the priming coat specified before coal tar epoxy coatings and floorings, bituminous membranes and damp-proof plastering. Mixed from its resin and hardener packs, the primer has a deliberately thin consistency — 50–100 cps at 25°C — so it wicks into the capillary structure of prepared concrete rather than filming over it. On metal, the same mix wets out cleaned steel and leaves a tar-toughened key for the protective build coats that follow.
Indian specifiers reach for it in two distinct situations. The first is aggressive wet service — sewage treatment plant tanks, effluent channels, marine structures — where the topcoat is a coal tar epoxy and the primer must match that chemistry. The second is dampness control: STP’s data sheet specifically recommends it on the interior face of basement walls before plastering. Space Arc Engineering stocks and applies it across Delhi NCR and pan-India.
The technical insight
The primer works by exploiting two chemistries at once. The epoxy fraction cross-links after the packs are combined — the 4-hour pot life marks that reaction window — and it is this cured network that anchors mechanically into concrete pores and chemically to subsequent epoxy or tar-based coats. The coal tar fraction contributes what epoxies alone lack: pronounced hydrophobicity, reflected in the TDS figure of nil water absorption, plus the anti-root behaviour useful under landscaped decks. Equally important is what sealing the pore structure prevents. Unprimed porous concrete releases trapped air as a topping cures, producing pinholes and blisters; a continuous primer film shuts those escape paths, which is why the data sheet insists on a second pass over any fast-absorbing patches that dry light-coloured.
Where it is used
- Priming concrete tanks, channels and floors in sewage and effluent treatment plants before coal tar epoxy coatings
- Priming cleaned structural steel and metal surfaces ahead of coal tar or bituminous protective systems
- Bond coat beneath waterproofing membranes on substructures, podiums and roofs
- Interior face of basement walls before plastering, as a dampness-check primer
- Sealing porous or absorbent concrete before chemical-resistant coal tar epoxy floor toppings
- Anti-root priming below planters and landscaped decks
- Concrete and steel in marine and portside structures in continuously wet service
Key advantages
- Low-viscosity 50–100 cps mix penetrates concrete capillaries instead of sitting on the surface
- Excellent adhesion to concrete gives coatings and membranes a dependable key
- Seals the pore structure and stops substrate air release — the usual cause of pinholes and blisters in toppings
- Nil water absorption once cured, adding a damp-check layer under plaster and finishes
- Economical coverage of 8–10 m²/L per coat keeps priming cost per square metre low
- 4-hour pot life with brush, roller or spray application suits both large crews and small patch gangs
- Applicable from 5°C to 40°C, covering most Indian site conditions through the year
Limitations & considerations
- Must not be applied where rising damp or osmosis is suspected, or where relative humidity exceeds 75%
- Unsuitable over asphalt, weak or friable concrete, unmodified sand-cement screeds, PVC tiles or sheets, and substrates that move appreciably, such as steel walkways
- Flash point of 25°C means the wet primer is flammable — ventilate the work area and exclude hot work nearby
- Coal tar chemistry is not accepted for potable water contact, so never specify it inside drinking water tanks
- New concrete needs 28 days of curing, or a verified moisture content below 5%, before priming
Selection & best practice
Preparation decides the result. Blow down dust and flakes with dry air, grind the surface smooth, and strip oil or grease by acid etching or burning, followed by a detergent wash, a clean-water rinse and mopping to a dry state. Confirm the concrete is at least 28 days old or below 5% moisture. Mix the two components for a full 3 minutes with a slow-speed drill (400–500 rpm) and a proper paddle until homogeneous, then apply immediately as a thin, continuous film by stiff brush, roller or spray — resist the urge to flood or paddle the material. Porous areas will drink the primer quickly and dry to light-coloured patches; give these a second coat, since starved spots are where adhesion fails and air-release bubbles start. Allow 6–8 hours of drying before the topcoat or membrane goes on, and keep the work within the 4-hour pot life.
Specifications
| Type | Two-component coal tar epoxy primer (resin + hardener) |
| Theoretical coverage | 8–10 m²/L per coat |
| Pot life | 4 hours |
| Mix specific gravity | 1.15–1.25 |
| Mix viscosity at 25°C | 50–100 cps |
| Application temperature | 5°C to 40°C |
| Flash point | 25°C |
| Drying time before overcoat | 6–8 hours |
| Packing / shelf life | 20 L drum; 12 months sealed, stored cool and dry |
Industry use cases
Sewage & Effluent Treatment
Primes digester walls, aeration tanks and channels before coal tar epoxy build coats, matching primer and topcoat chemistry in biologically aggressive service.
Basements & Substructures
Applied to the internal face of basement walls ahead of plastering, and under substructure membranes, to check dampness migrating through porous concrete.
Marine & Ports
Preps jetty steel and splash-zone concrete for tar-based anti-corrosive coatings in permanently wet, saline exposure.
Industrial Flooring
Seals absorbent slabs before chemical-resistant coal tar epoxy toppings in process plants, preventing pinholes in the wearing coat.
Podiums & Landscaped Decks
Provides an anti-root priming layer beneath membranes under planters and green decks.
Frequently asked questions
How much area does one 20 L drum cover?
How soon can I overcoat or lay the membrane?
Can it go on fresh or damp concrete?
Is ShaliPrime CT suitable for drinking water tanks?
Which topcoats work over it?
What is the working time after mixing?
How we position STP ShaliPrime CT
ShaliPrime CT is the entry coat of STP’s coal tar family: pair it with ShaliPoxy CTE coatings for sewage and marine tank linings, or with ShaliMastic HD where a heavy-bodied anti-corrosive coal tar coating is the finish. For torch-applied bituminous membrane work, STP’s Shalitex Primer is the more conventional bitumen-based choice. Projects standardising on Fosroc can achieve the same protection with Nitocote ET140 coal tar epoxy. Space Arc Engineering supplies and applies all of these systems across Delhi NCR and pan-India, and can advise on the right primer-topcoat pairing for your exposure.
Fosroc Nitocote ET140 — Specifiers running a single-source Fosroc protection package on sewage or marine work often choose Nitocote ET140, a coal tar epoxy coating applied as its own multi-coat system rather than a separate primer plus topcoat.
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