About STP ShaliDCT 105

STP ShaliDCT 105, previously marketed as ShaliKote CT 105, is a processed saturated tar from STP Limited that has been specifically refined to work alongside polyurethane chemistry. On its own, coal tar is a proven barrier material with a long track record in the protection of buried and immersed assets, but ordinary tar contains reactive fractions that quarrel with isocyanate-based binders, leaving PU systems soft, tacky or under-cured. ShaliDCT 105 is processed to strip out that incompatibility, so specifiers can combine the toughness and chemical resistance of a PU film with the low permeability and economy of coal tar in a single engineered system.\n\nBecause it is a system component rather than a stand-alone finish, ShaliDCT 105 is almost always specified together with the polyurethane resin it is designed to pair with, mixed on site in the ratio STP prescribes for that system. It is a solvent-free grade, which keeps the mixed material high in solids and low in VOC-driven shrinkage, an advantage on thick-film corrosion-protection work where film build and edge retention matter. For engineers and applicators in India working on pipelines, effluent tanks and marine concrete, it offers a familiar coal-tar performance profile in a form that will not compromise a modern polyurethane topcoat.

The technical insight

The value of ShaliDCT 105 lies in how it resolves a long-standing chemistry conflict. Polyurethane coatings cure when isocyanate groups react with a co-reactant to build a cross-linked film; raw coal tar carries free phenolics, acids and moisture-active species that consume or poison those isocyanate groups, so a naive tar-plus-PU blend never reaches full hardness. STP’s processing saturates and stabilises the tar, neutralising the fractions that would otherwise interfere, so the isocyanate reaction proceeds to completion. The result is a hybrid film that keeps the dense, hydrophobic, ionically resistant backbone of coal tar, which is what slows water and chloride ingress to buried steel, while gaining the abrasion resistance, adhesion and flexibility of the cured urethane matrix. Solvent-free formulation reinforces this: with no carrier to flash off, the applied film shrinks little and stays close to its wet thickness, which is critical for the high dry-film builds that corrosion-protection specifications demand.

Where it is used

• Coal-tar polyurethane anti-corrosive coating systems for buried and immersed steel
• Protective lining of effluent, sewage and industrial waste-water structures
• Waterproofing and corrosion protection of concrete water-retaining tanks
• External protection of steel pipelines and pipe supports in aggressive soils
• Marine, splash-zone and jetty steelwork requiring a chemically resistant barrier
• Below-grade concrete surfaces exposed to contaminated or aggressive groundwater
• Steel and RCC assets in chemical and effluent-handling plants
• As the tar phase in field-blended PU coal-tar barrier systems specified by STP

Key advantages

• Chemically compatible with isocyanate-cured polyurethane, so the PU phase cures fully
• Delivers the proven low permeability and anti-corrosive barrier of coal tar
• Solvent-free grade with high solids and low film shrinkage on thick builds
• Combines coal-tar economy with PU toughness in one engineered system
• Strong resistance to water, effluent and aggressive ground conditions
• Suited to both steel and concrete substrates
• Backed by STP Limited, an established Indian protective-coatings manufacturer
• Supplied with technical support and Pan-India logistics through Space Arc Engineering

Limitations & considerations

• Not a stand-alone coating; it must be used with its matching polyurethane component in the prescribed system
• As a coal-tar-based product it is dark in colour and unsuitable where a light or decorative finish is required
• Coal-tar chemistries face tightening environmental and handling scrutiny; confirm suitability for potable-water and enclosed-space use before specifying
• Performance depends heavily on correct substrate preparation, priming and mix ratio
• Published coverage, film-thickness and cure-time figures are project- and system-specific; always work to the current STP technical data sheet
• Requires trained applicators and appropriate PPE and ventilation during mixing and application

Selection & best practice

Specifications

Industry use cases

How we position STP ShaliDCT 105

STP ShaliDCT 105 sits in Space Arc’s protective and anti-corrosive coatings range as the coal-tar building block of STP’s polyurethane coal-tar systems, best specified alongside its matching STP polyurethane resin and compatible STP primers such as the ShaliPrime range for coal-tar and steel substrates. Within the wider STP coal-tar family it complements other ShaliDCT grades (for example ShaliDCT 102, 102A and 104) that address different coating roles and viscosities, so specifiers can match the exact grade to the assembly. Where a project prefers a single-supplier epoxy route, our Fosroc line offers a comparable coal-tar-extended solution.

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