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Why coatings fail: craters, fisheyes, pinholes – and how fluorinated wetting agents fix them

Paints and Coatings

Even when your resin, pigment, and cure package are “correct, ” a coating can still fail for one frustrating reason: surface energy mismatch. The wet film can’t flow and wet the substrate uniformly, so it pulls away from tiny contaminants or trapped air—and defects appear. Three of the most common surface- defect families are: Craters: shallow, round depressions (often with a raised rim). Fisheyes: craters with a distinct “clean” center—classic signature of silicone/oil contamination. Pinholes: tiny holes that go down into the film, often from air/gas release or foam collapse.

The good news: in many systems, fluorinated wetting agents are one of the most reliable tools to prevent and repair these defects because they reduce surface tension hard, improve wetting, and stabilize flow before the film sets.

What’s really happening in the wet film

Craters and fisheyes: “dewetting” events

A crater/fisheye happens when a local spot has lower surface energy (e.g., oil, silicone, release agent, wax, skin oils). The coating retracts from that spot, creating a circular defect.
Common triggers

  • Silicone oils (polish, mold release, defoamer overdose, lubricants)
  • Grease/oil (handling, compressor oil, machine mist)
  • Surfactant incompatibility (wrong additive balance)
  • Poor substrate cleaning or weak pretreatment

Pinholes:“bubble pathways”

Pinholes are typically caused by entrapped air or gas release that doesn’t escape before viscosity rises / cure starts.
Common triggers

  • Porous substrates (wood,concrete,cast parts)
  • Solvent popping (fast solvent,high film build,hot surface)
  • Foam/air entrainment (high shear,wrong defoamer sequence)
  • Moisture/CO2 release (some 2K systems, reactive substrates)

Why fluorinated wetting agents work (and when they don’t)

Fluorinated wetting agents have extremely low surface energy. In a coating, they help by:

  • Lowering dynamic surface tension quickly (important during spray + flash-off)
  • Improving substrate wetting (especially low-energy plastics,oily/unknown surfaces)
  • Improving flow-out so the film can“heal”before set
  • Reducing sensitivity to minor contamination events

They are not magic.If contamination is heavy (e.g., strong silicone release,oil pooling),you still need cleaning + process control.Think of fluorinated wetting agents as defect insurance—not a substitute for hygiene.

Dosage guidance (practical starting points)

Because products vary (100% active vs pre-diluted),it’s best to dose on“active content”.Below are typical starting ranges used across many coating types:

Recommended starting ranges (as active matter on total formulation)

  • 0.02–0.05% active: mild improvement in flow/wetting,minimal side effects
  • 0.05–0.12% active: strong crater/fisheye resistance (common sweet spot)
  • 0.12–0.20% active: tough cases / low-energy substrates; monitor foam,intercoat adhesion, recoatability
  • >0.20% active: usually not needed; risk of foam stabilization,excessive slip,intercoat adhesion loss,print resistance issues

Quick conversion examples

  • If your additive is 100% active: use the % above directly.
  • If your additive is 50% active: double the addition level (e.g.,0.10% active ≈ 0.20% product).
  • If your additive is 30% active: multiply active target by 3.33 (e.g.,0.06% active ≈ 0.20% product).

Best practice: run a ladder test: 0.03%,0.06%,0.10% active

Where and how to add ?

Goal: distribute the wetting agent uniformly without creating foam.

  • Add during letdown (after pigment dispersion) or as a post-add under low shear.
  • Pre-dilute in a compatible solvent/resin (if recommended by supplier) for better distribution.
  • Avoid dumping into a high-shear vortex—many surface additives can trap air if handled aggressively.
  • If you use a silicone defoamer,check sequence:
    Often works best: wetting agent → mix → then defoamer fine-tune
    But if foam becomes an issue, reverse can help.Always validate in your system

For more details,please contact us:

Geocon Group

  • R-2057, Akshar Business Park, Opp. APMC Fruit Market, Sector 25, Vashi, Navi Mumbai – 400 703, Maharashtra, India