STP ShaliMastic HD/LC
Heavy-duty thermoplastic coal tar pitch coating in high-build (HD) and low-build (LC) grades — cold-applied, single-component protection for buried and submerged steel and concrete against seawater, soil chemistry and marine organisms.
What is it?
A single-component, cold-applied anti-corrosive coating based on specially processed coal tar pitch. Two grades: HD builds 200-250 microns per coat; LC lays down an economical 40-60 micron film.
Where is it used?
Buried and submerged steel and concrete — tank interiors and exteriors, steel pilings, culverts, sluice gates, filter screens, trestles, tank bases, barges and underwater structures.
Why use it?
Coal tar pitch is practically inert to seawater, acids, alkalis, soil bacteria and marine organisms, and the thermoplastic film stays pliable, absorbing thermal movement without cracking.
How is it applied?
Brush or metal plate (patra) over a hard-dried coat of ShaliPrime PW CT primer; minimum 3 coats on metal and 2 on concrete, applied between 10 °C and 50 °C ambient.
About STP ShaliMastic HD/LC
ShaliMastic HD/LC is STP Limited’s workhorse anti-corrosive coating for structures that spend their service life underground or underwater. Built on specially processed coal tar pitch — the chemistry STP has refined since its Shalimar Tar Products days — it comes in two grades from the same family: ShaliMastic HD, a thixotropic high-build mastic that generally conforms to the US Bureau of Reclamation specification for Cold Applied Coal Tar Compound CA-50, and ShaliMastic LC, a brushable low-build liquid conforming to IS 290.
Space Arc Engineering supplies both grades in 20 L and 200 L drums across Delhi NCR and pan-India, with applicator support for tank farms, water infrastructure and marine works. The typical buyer is a contractor protecting buried fuel-storage tanks, an irrigation department coating sluice gates and culverts, or a port maintenance team recoating pilings — jobs where a proven, single-pack barrier coating matters more than gloss or colour.
The technical insight
Coal tar pitch owes its protective performance to a dense polyaromatic structure that water molecules struggle to penetrate and that soil bacteria and marine borers cannot metabolise — which is why it remains a reference chemistry for buried service decades after most alternatives arrived. Because the film is thermoplastic rather than chemically cured, it never embrittles the way a thermoset can: it keeps its pliability across a wide temperature range and rides expansion and contraction of the substrate without cracking. Protection is purely barrier-type, so film continuity is everything — the HD grade’s thixotropy lets it hold 200-250 microns per coat without sagging, building a void-less, joint-less envelope, while LC’s 40-60 micron film suits large areas where economy governs.
Where it is used
- External protection of buried metal storage tanks for diesel, petrol and other liquids or gases
- Interior and exterior coating of metal and concrete tanks in water and process infrastructure
- Steel pilings, trestles and tank bases in coastal and high-water-table locations
- Culverts, sluice gates and filter screens in irrigation and water-treatment works
- Barges and underwater structures, inside and out
- Buried or submerged plant equipment and pipework surfaces
- Concrete in contact with aggressive soils, sulphate-bearing groundwater or effluent
Key advantages
- Unaffected by marine organisms, soil chemicals and soil bacteria — suited to permanent burial or immersion
- Highly resistant to corrosion from seawater, acids and alkalis
- Thermoplastic film retains pliability over a wide temperature range, taking movement without cracking
- Forms a tough, abrasion-resistant coat that survives backfilling and handling
- Void-less, joint-less continuous film — no seams or overlaps to fail
- Single-component and cold-applied: no mixing ratios, pot life or heating equipment on site
- Two grades from one system — HD at 200-250 microns/coat for severe duty, LC at 10 m²/L on metal for economical large-area work
- 12-month shelf life in sealed drums simplifies project stocking
Limitations & considerations
- Coal tar based — strict PPE, ventilation and skin-contact precautions are mandatory during application
- Not certified for potable-water contact; do not specify inside drinking-water tanks without separate confirmation from STP
- Black only, and like all coal tar coatings it is at its best buried or submerged rather than in permanent direct sunlight
- Must not be applied over shop coatings, particularly red oxide primer — these must be removed first
- Application window is 10-50 °C ambient, and HD needs 24 hours to dry through, so multi-coat schedules span several days
- 65 °C flash point means flammable-goods storage and hot-work controls apply
Selection & best practice
Surface preparation decides the outcome. Grind or blast the base metal, then remove dust, flakes, oil and grease by sand blasting, wire brushing or compressed air. Stir each drum with a slow-entry high-speed mixer (about 150-200 rpm) for 5 minutes, keeping the paddle submerged to avoid dragging air into the mass, then let it settle for 10 minutes. Prime with ShaliPrime PW CT and give it a minimum 4 hours to hard-dry before the first coat. Apply by brush or metal plate (patra): at least 3 coats on metal, 2 on concrete, respecting the touch-dry interval between coats (6 hours for HD, 3 for LC). Never coat over red oxide shop primer, and keep application between 10 °C and 50 °C.
Specifications
| Form / colour | Black thixotropic mass (HD) / black thixotropic liquid (LC), brush-applicable |
| DFT per coat | HD: 200-250 micron; LC: 40-60 micron |
| Theoretical coverage on metal | HD: 3 m²/L; LC: 10 m²/L |
| Theoretical coverage on concrete | HD: 2 m²/L; LC: 8 m²/L |
| Drying time (touch / thorough) | HD: 6 h / 24 h; LC: 3 h / 12 h |
| Specific gravity | HD: 1.30; LC: 1.14 |
| Flash point | 65 °C (both grades) |
| Standards | HD: generally conforms to USBR Cold Applied Coal Tar Compound CA-50; LC: IS 290 |
| Packing / shelf life | 20 L and 200 L drums; 12 months in unopened sealed condition |
Industry use cases
Fuel storage & depots
External barrier coating on buried diesel and petrol storage tanks at retail outlets, terminals and depots, where soil moisture and stray chemistry attack bare steel.
Irrigation & water infrastructure
Sluice gates, culverts, filter screens and tank bases for irrigation departments and water boards — LC grade covers large steel areas economically at 10 m²/L.
Ports & marine works
Steel pilings, jetty trestles and barge hull surfaces where marine organisms and seawater immersion rule out most conventional paints.
Power & process plants
Buried pipework, submerged equipment and concrete foundations in contact with aggressive soils — HD grade builds a heavy-duty envelope in 3 coats.
Sewage & effluent handling
Concrete tank interiors and exteriors exposed to acidic or alkaline effluent, where coal tar’s chemical inertness outlasts cementitious coatings.
Frequently asked questions
Should I choose HD or LC?
How much material do I need?
Is a primer required?
Can I apply it over an existing red oxide shop coat?
Can it be used inside drinking-water tanks?
How does it differ from a coal tar epoxy?
How we position STP ShaliMastic HD/LC
ShaliMastic HD/LC sits at the heart of STP’s coal tar protection system: pair it with ShaliPrime PW CT, the primer the TDS mandates, and look to STP’s wider coal tar range (ShaliPitch, TarStil Tar) for allied pipeline and industrial duties. Where a consultant specifies a chemically cured film for immersed service — higher abrasion, solvent splash or a tighter DFT spec — Fosroc Nitocote ET550 coal tar epoxy is the natural step up, and both are available through Space Arc with applicator support across Delhi NCR and pan-India.
Fosroc Nitocote ET550 — Specifiers who need a chemically cured, harder-wearing film for immersed or abrasion-prone service often step up to this two-pack coal tar epoxy in place of ShaliMastic’s single-pack thermoplastic.
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