A small circular crater appears in an otherwise glass-smooth epoxy pour, exposing the substrate underneath like a tiny window. That defect has a name — the fisheye — and it is one of the most common, and most preventable, failures in epoxy finishing.

The Mechanism: Surface Tension Repulsion

A fisheye forms when the liquid epoxy actively pulls away from a foreign substance rather than wetting out over it. The mechanism unfolds in three stages:

1. Contaminant Barrier: Substances such as silicone, oil, grease, wax, or residual cleaning agents create a microscopic film on the substrate. These contaminants have a much lower surface tension than the liquid epoxy resin.
2. Epoxy Repulsion: As the epoxy attempts to achieve a uniform surface tension across the panel, it reacts strongly to the low-energy contaminant spot. Resin molecules pull away from the contaminated area toward the surrounding clean epoxy, opening a void or crater at that point.
3. Common Sources: Silicone is the most notorious culprit — traces can come from furniture polish, caulking, mold-release sprays, or even residue on skin and hair. Fingerprint oils, machine oils, cutting fluids, and wax residue are close behind. Excess ambient moisture or condensation can trigger a milder version of the same effect.

Prevention: Decontamination Before the Pour

Meticulous surface preparation is the only reliable way to stop fisheyes before they start.

• Sand and Vacuum: Sand the substrate to create a mechanical profile and remove the bulk of any surface film, then vacuum away the dust.
• Solvent Wipe: Wipe the entire surface with acetone or high-purity isopropyl alcohol (IPA) to dissolve any residual oils or grease. Use a clean, lint-free cloth, and discard it after one or two passes — do not touch the cleaned surface with bare hands, since skin oils recontaminate it instantly.
• Isolate Silicone Sources: Remove every silicone product from the work area, including sprays, caulking, and any tools that have previously contacted them, since even trace transfer onto a glove or spreader can seed a new fisheye.

A Fast Way to Verify a Surface Is Actually Clean

A visual inspection is not enough to catch a thin oil film — the water-break test is a faster, more reliable check. Mist the prepared surface with clean water: if it sheets evenly across the substrate, the surface is free of low-energy contaminants; if the water beads up or breaks into isolated droplets, contamination remains and another cleaning pass is required before the pour. Running this test on a sample corner before committing to a full production pour catches marginal cleaning in seconds rather than after the epoxy has already gelled around a defect. Email Us if your team wants a walkthrough of surface-verification methods suited to your specific substrate and finish requirements.

Repairing a Fisheye That Has Already Formed

If fisheyes appear while the epoxy is still wet, a quick, sweeping pass with a torch or heat gun can lower the resin’s viscosity enough for it to flow back and partially fill the void — though this fix is often only partially effective on deeper craters.

Once the epoxy has fully cured, a more dependable repair uses a second-coat method:

1. Decontaminate: Thoroughly clean the cured surface to remove any remaining oil or silicone barrier, using a mild detergent wash followed by an acetone wipe.
2. Sand: Lightly sand the entire surface with 180–220 grit sandpaper to open a fresh mechanical profile.
3. Apply a Fresh Coat: Pour a new, thin coat of epoxy. The sanding and cleaning provide enough surface energy for the fresh epoxy to wet out and fill the craters left by the first coat.

Commercial additives sold as “fisheye killer” or defoamer can be mixed into the batch as a low-surface-tension additive that makes the entire pour tolerant of the contaminant. This approach is controversial for a reason: it can weaken the final cured film’s clarity and hardness, so treat it as a last resort rather than a substitute for proper decontamination.

Selecting a Formulation That Tolerates Real-World Shop Conditions

Not every epoxy responds to contamination the same way. Formulations with a slightly lower surface tension and better wetting characteristics are inherently more forgiving of the trace oils and dust that are difficult to eliminate entirely in a working shop or garage environment, particularly for readers comparing a UV-cure adhesive against a two-part epoxy for a transparent, glass-clear finish. For thicker decorative pours where cure speed and surface leveling both matter, it is also worth reviewing how different UV lamp configurations affect resin curing outcomes, since uneven light exposure can compound a contamination-driven surface defect into a larger cosmetic failure.

Incure formulates its epoxy and UV-cure resin systems with consistent wetting behavior in mind, but no chemistry can fully substitute for correct surface preparation — a clean, contaminant-free substrate remains the foundation of a defect-free pour. Contact Our Team if you need help specifying a system suited to your shop’s typical contamination risks and production volume.

Visit www.incurelab.com for more information.