• Mechanical Cleaning (St 2 / St 3): Hand- and power-tool cleaning using wire brushes, scrapers, scaling hammers, or pneumatic needle guns. St 2 represents thorough scraping and wire-brushing, while St 3 requires very thorough cleaning until a faint metallic sheen appears. This is the standard operational baseline for onboard touch-up maintenance;
• Abrasive Blast-Cleaning (Sa 2.5): The drydock gold standard (“Near-White Metal”). Steel is blasted with grit or copper slag until 95% of every section is free of all visible residue, mill scale, and rust. This process creates the required surface anchor profile (roughness of 50–75 μm), allowing the primer to mechanically key into the metal;
• Ultra-High Pressure Hydroblasting (UHP Water Jetting): Stripping paint and rust using fresh water pressurized above 2,000–2,500 bar. This method eliminates airborne dust and washes out entrained chlorides, but requires immediate moisture-tolerant primers to prevent flash rust.

The primer acts as both adhesive and shield. Its primary objectives are substrate adhesion and active corrosion inhibition. The most common marine primers are two-pack epoxy primers, forming an impermeable moisture barrier. Additionally, zinc-rich primers provide galvanic (cathodic sacrificial) protection: the zinc particles oxidize preferentially, shielding the underlying steel substrate.

The intermediate coat increases total dry film thickness (DFT), slows moisture vapor transmission, and enhances intercoat adhesion between heavy barrier primers and cosmetic finish coats. In shipboard practice, intermediate coats are tinted in a contrasting shade: if the finish layer experiences mechanical abrasion, the deck watch immediately spots the damage before rust can form.

The topcoat provides color retention, gloss, and resistance to environmental degradation. On superstructures and bulwarks, two-pack aliphatic polyurethane paints are standard: they resist solar ultraviolet radiation without chalking or yellowing. For working decks and walkways, tough epoxy finishes incorporate silica sand to generate non-skid (anti-skid) textures.

Applied exclusively below the deep waterline to deter biofouling. Historically reliant on organotin compounds (TBT was banned globally under the IMO AFS Convention), modern technologies operate under two primary mechanisms:

• Self-Polishing Copolymers (SPC): Under the mechanical action of water flow, the outer binder micro-layer slowly hydrolyzes and washes away, constantly exposing fresh active biocide. SPC coatings require regular vessel movement at sea to remain effective;
• Fouling Release Systems (FRS / Silicone): Biocide-free, non-toxic technologies. The silicone surface is ultra-smooth and low-surface-energy, preventing barnacles, tubeworms, and macroalgae from bonding. Slime and fouling wash off dynamically once ship speed exceeds 10–12 knots.

Engine exhaust gas manifolds, steam lines, and boiler uptakes reach operating temperatures where alkyd and standard epoxy coatings carbonize above 200°C. Specialized silicone-aluminum and inorganic silicate formulations are required, withstanding continuous exposure up to 600°C without blistering or delaminating.

Tank linings represent the highest tier of marine coating technology. Linings must remain chemically inert, prevent product contamination (such as aviation fuel Jet A-1, potable alcohol, or edible oils), and resist hot chemical washings. Detailed washing and tank turnaround protocols are outlined in our practical tank cleaning guide for chemical tankers.

• Coating work inside enclosed spaces (ballast tanks, cofferdams, forepeak) constitutes hazardous work: a formal Enclosed Space Entry Permit must be logged, with continuous forced ventilation and gas monitoring for LEL, O₂, and toxic vapors;
• Certified Personal Protective Equipment (PPE) is mandatory: organic vapor respirators with particulate pre-filters (A2P3), chemical-resistant nitrile gloves, and eye protection;
• Inside paint lockers and cargo holds, only certified explosion-proof (Ex-rated) lighting and grounded pneumatic equipment are permitted. Prior to beginning hazardous painting tasks, review procedural requirements using the Marine Risk Assessment Tool.

• Visual Appearance: Hemispherical bubbles varying from pinhead size to several centimeters across, frequently containing trapped liquid;
• Root Cause: Osmotic pressure. Coating over unwashed marine salts, moisture condensation (violating the dew point rule), or solvent entrapment from applying topcoats before the primer releases volatiles;
• Remedial Action: Scrape open blisters, blast or needle-scale back to bare steel (St 3 / Sa 2.5), wash thoroughly with fresh water to remove soluble salts, dry, and reapply the specified coating system.

• Visual Appearance: A friable, chalk-like white powder on the surface, causing loss of gloss and color fading;
• Root Cause: Photochemical degradation of the polymer binder under solar ultraviolet (UV) radiation. Standard epoxy resins chalk rapidly when exposed to sunlight;
• Remedial Action: Wash down with fresh water under pressure using abrasive scrubbers to remove loose powder, then apply an aliphatic polyurethane topcoat.

• Visual Appearance: Interconnected crack patterns resembling the scales of an alligator hide;
• Root Cause: Tensile stress mismatch. Applying a hard, rigid coating (such as an epoxy) over a soft, flexible, or uncured primer (like bitumen or alkyd). The topcoat contracts faster during curing than the flexible sub-layer can accommodate;
• Remedial Action: Completely remove the failed coating layers down to a sound substrate or bare metal, and reapply compatible layers.

• Visual Appearance: Downward curtain-like runs, teardrops, and heavy ridges on vertical surfaces;
• Root Cause: Excessive wet film thickness (WFT), adding too much thinner, or holding the spray gun too close to the bulkhead;
• Remedial Action: Allow the paint to cure completely, sand down the runs until the surface is flush, and reapply a uniform, controlled coat.