What to check on a Epoxy Anticorrosive Primer.
Within a paint and coating system, the primer is the layer that has to bond to bare steel rather than to another coat of paint, so its chemistry is built around adhesion and corrosion inhibition rather than gloss, colour or abrasion resistance. Two-component epoxy primers cure through a chemical reaction between resin and hardener rather than solvent evaporation alone, giving a dense film with low permeability to water and oxygen, the two ingredients corrosion needs to get started on unprotected steel.
What sets an epoxy anticorrosive primer apart
Within a paint and coating system, the primer is the layer that has to bond to bare steel rather than to another coat of paint, so its chemistry is built around adhesion and corrosion inhibition rather than gloss, colour or abrasion resistance. Two-component epoxy primers cure through a chemical reaction between resin and hardener rather than solvent evaporation alone, giving a dense film with low permeability to water and oxygen, the two ingredients corrosion needs to get started on unprotected steel.
Main components of the system
Resin and hardener
Supplied as two components mixed shortly before application, typically an epoxy resin base and a polyamide or amine hardener, with a limited pot life once combined.
Anticorrosive pigment
Zinc phosphate, zinc dust or similar pigments carried in the film to inhibit corrosion at the steel surface, either by sacrificial action or by forming a passive layer.
Surface tolerance versus standard grades
Standard epoxy primers require near-white or better blast cleaning and a dry surface, while surface-tolerant epoxy primers accept some residual rust, moisture or hand tool preparation, at the cost of a shorter expected service life.
Selection and sizing
- Surface preparation achievable in the actual application conditions, drydock blast versus afloat touch-up, which decides between standard and surface-tolerant grades.
- Dry film thickness specified per coat, since epoxy primers are typically applied to a target range and under-thickness leaves inadequate barrier protection.
- Compatibility with the topcoat system, since not every finish coat is formulated to bond to every primer chemistry.
- Service environment: ballast tank, cargo tank, external hull or deck, each with a different exposure and a matching primer specification.
Regulations and class
IMO's Performance Standard for Protective Coatings applies to dedicated seawater ballast tanks and double-side skin spaces on bulk carriers, and to void spaces on tankers, setting minimum coating system life, surface preparation grade and dry film thickness requirements that an epoxy primer must be part of to achieve a Good condition rating. Class societies survey coating condition in these spaces on a defined schedule, and coating breakdown found during survey can trigger earlier renewal requirements than originally planned.
Typical faults
| Fault | Consequence |
|---|---|
| Insufficient blast profile or contamination left on steel | Poor adhesion, early flaking and pinpoint rusting through the film |
| Primer applied below minimum dry film thickness | Reduced barrier protection, corrosion breakthrough ahead of schedule |
| Overcoating interval exceeded before topcoat application | Poor intercoat adhesion, delamination between primer and topcoat |
| Application in high humidity or near dew point | Moisture entrapment in the film, blistering during service |
What to look for in a supplier
- Approval to the IMO Performance Standard for Protective Coatings where the primer is intended for ballast tanks or void spaces covered by that standard.
- Clear technical data on surface preparation grade, dry film thickness range and overcoating window.
- Documented compatibility with the specific topcoat system intended for the project, confirmed rather than assumed.
- Batch traceability and technical field support during application, since primer failures are as often a workmanship issue as a product issue.
Dry film thickness is worth checking wet during application with a comb gauge as well as after cure, since a thin patch found only after the topcoat is on means stripping back through both coats to fix it.