Zinc-rich primers

Hempel's inorganic zinc Galvosil 15700 lists 50–100 µm dry film, 50 µm recommended, and 125 µm DFT maximum local thickness. Its cure needs above 50% RH. At 20°C and 50 µm, it lists about 30 minutes touch dry, 60 minutes hard dry and 24 hours fully cured. Verify film build, surface preparation and moisture during cure. Hempel, Galvosil 15700 PDS, pp. 2–3

Protection depends on a conductive coating system

Sacrificial protection requires electrical contact among zinc particles and steel, with moisture as electrolyte. Zinc corrosion products can also contribute a barrier. Qualify the coating's preparation and continuity. ZRC Worldwide, Frequently Asked Questions, galvanic action and conductivity

Teamac likewise emphasizes direct contact with iron or steel for its zinc-rich primer. As an engineering implication, placing an arbitrary insulating coating between steel and zinc primer cannot be assumed to preserve the intended galvanic function. Approved shop primers, repair overlaps, and existing coatings need the selected manufacturer's system guidance. Teamac, Zinc Rich Primer.

Inorganic silicate versus organic epoxy

Wattyl describes the silicate matrix and moisture-dependent curing of its inorganic zincs. Jotun describes Barrier 80 S as a two-component, polyamide-cured, ceramically reinforced zinc-rich epoxy. These are distinct formulation families; a zinc-silicate binder and an epoxy hardener are not interchangeable components. Wattyl, Zinc Silicates: Properties/Application, I-16; Jotun, Barrier 80 S TDS, October 2, 2026.

Zinc content: state what the percentage measures

Wattyl defines zinc-rich content in terms of metallic zinc by weight in the cured film. This is different from zinc percentage in the wet can, volume solids, zinc-dust purity, or pigment percentage alone. Specify the required measurement basis and applicable standard rather than comparing unlabeled percentages. Wattyl, I-16, properties.

For example, the Barrier 80 S TDS reports 67 ± 2% solids by volume and compliance with the compositional requirements of SSPC Paint 20, Level 2, plus ASTM D520 Type II zinc dust. These are different statements. The solids figure is not the metallic-zinc mass fraction; the dust standard is not a corrosion-system qualification. Do not infer an exact dry-film zinc percentage from the product's “80” name alone. Jotun, Barrier 80 S TDS, product description and data.

Preparation and application

Jotun's Barrier 80 S Application Guide, October 2, 2026, calls for removal of contamination and abrasive blasting with a sharp angular profile for its recommended carbon-steel preparation. It distinguishes minor mechanically prepared repairs from full-area preparation. It also says the product is not intended for full overcoating of galvanized or inorganic-zinc-coated surfaces; its repair procedure addresses damage exposing bare metal. Suitability for a galvanized-steel repair therefore does not authorize coating an entire intact galvanized structure. Jotun, Barrier 80 S AG, pp. 1–3.

Hempel's inorganic-silicate guideline requires thorough liquid-component stirring, slow addition of zinc dust with mechanical mixing, and continued agitation to prevent settling. Its instructions use complete supplied packs and protect the mixture from moisture before application. Follow the chosen product's instructions; settling zinc makes uncontrolled application a composition-control problem as well as a spray-quality problem. Hempel, Inorganic Zinc Silicates Technical Guideline, March 2025, p. 1.

Bounded thickness and cure example: Galvosil 15700

The downloaded Galvosil 15700 US PDS is issued October 2026. It specifies:

The Galvosil laboratory timing uses 20°C and 50 µm DFT. Verify humidity and the actual cure before overcoating. Hempel, Galvosil 15700 PDS, pp. 2–3

More film is not automatically more protection. Wattyl identifies excessive build, poor drying conditions, low blast profile, and inadequate ventilation among causes of mud cracking. Inspect corners and overlaps for build-up, and distinguish rough dry spray from sound film. Wattyl, I-16, application problems.

Cure verification and subsequent coats

Hempel's silicate guideline requires full cure before use or overcoating and specifies an ASTM D4752 resistance rating of at least 4 for its cure check. It explains that porous, non-weathered zinc silicate can cause popping in subsequent coats. A compatible mist/flash coat or dedicated sealer may be needed; some epoxy barrier products are unsuitable for that technique. This is supplier guidance, not a universal dilution recipe. Hempel, inorganic-silicate guideline, pp. 2–3.

Galvosil's PDS requires removal of zinc salts and contamination before overcoating. Jotun's epoxy guide separately defines maximum intervals by subsequent coating and temperature. It warns that excess zinc-epoxy thickness can cause cracking and poor integrity. Apply each layer within the specified window and condition the surface as directed when that window is exceeded. Hempel, Galvosil PDS, p. 3; Jotun, Barrier 80 S AG, film control and overcoating.

System and service boundaries

Barrier 80 S's TDS describes an atmospheric primer and limits NORSOK prequalification to selected systems. Galvosil's ISO 12944 and NORSOK statements likewise concern predefined coating systems. Neither statement establishes the performance of an arbitrary primer/intermediate/topcoat combination. Jotun, approvals; Hempel, approvals.

As engineering synthesis, retain the tested system, layer thicknesses, substrate preparation, exposure category, and acceptance criteria together. Do not translate salt-spray hours into years of field life or treat zinc loading as a standalone ranking. Specify immersion chemistry, temperature, abrasion, appearance, repair needs, and approved topcoat; read the current SDS for each component and solvent. A zinc-rich primer is one part of a qualified protection system.