A crater that exposes bare substrate through an otherwise perfect pour has one root cause almost every time — contamination — and tracing it down is more reliable than guessing at a fix.
Fisheyes, splotches, weird textures, and small round defects are among the most frustrating issues in epoxy work. Similar to dimples, these defects are almost always the direct result of contamination — a localized surface-tension failure where liquid epoxy retreats and pulls away, leaving a crater-like defect that often exposes the substrate beneath. Controlling contamination is the key to a consistently smooth, professional finish.
Why Fisheyes and Splotches Appear
The phenomenon where epoxy pulls away from a contaminated spot is known as crawling or cratering. It happens because the surface energy of the contaminant, such as oil, is much lower than the surface energy of liquid epoxy, causing the resin to be repelled.
1. Silicone and Oil Contamination
This is the most frequent and persistent cause. Trace amounts of mold-release wax, spray silicone lubricants, or furniture polish transferred from hands, tools, or the air are common culprits. Silicone can travel surprisingly far through HVAC systems or drafts — if a silicone caulk was used nearby, or aerosol cooking sprays are in use, particles can settle on wet epoxy from across a room. Reused mixing cups or dirty stir sticks carry residue from previous projects, and fingerprints, hand lotions, skin oils, or machine lubricants on the substrate itself are just as effective at causing the defect.
2. Moisture and Humidity
Less common for sharp fisheyes but still a factor: if the substrate, especially wood, has high moisture content, that moisture leaches out during the epoxy’s exothermic cure and disrupts the surface, producing a splotchy, uneven texture. High ambient humidity can react with amine-based hardeners directly, producing a hazy, waxy film known as amine blush — not technically a fisheye, but a related weird-texture problem.
3. Substrate Outgassing
This typically produces a pattern of small, round defects resembling permanent bubbles or craters. Porous materials — wood, concrete, composites — contain trapped air that expands as the exothermic cure heats the substrate, pushing out through the liquid epoxy and creating a bubble that, once popped, may leave a crater that doesn’t fully collapse before gelling. Without a preliminary seal coat on a porous material, outgassing during the main flood coat is essentially inevitable.
Genuine Solutions for Flawless Epoxy Surfaces
Eliminating fisheyes and texture issues takes a multi-pronged approach focused on cleanliness, preparation, and technique.
1. Zero-Tolerance for Contamination
Before pouring, meticulously wipe the substrate with a clean cloth and a recommended solvent — acetone or denatured alcohol — using only high-purity product and waiting for full evaporation before applying epoxy. Keep every nearby item clean, including gloves and tools, and wear non-powdered nitrile gloves to avoid transferring skin oils or lotion. Isolate the workspace from silicone sealants, spray lubricants, and even air fresheners during the pour and cure.
2. Substrate and Moisture Management
For wood, concrete, or other porous materials, always apply a thin, quick-curing seal coat first, penetrating the pores and trapping the air before the main layer goes on — wait for it to gel or cure enough to block air before the flood coat. Check wood moisture content with a meter, aiming below 10% to minimize outgassing and moisture-related texture problems, and run a dehumidifier if ambient humidity climbs above 50–60%.
3. Application and Repair Techniques
If fisheyes appear immediately after pouring, a quick torch sweep can temporarily reduce surface tension at the defect and let epoxy flow back into the crater. For minor, widespread contamination, waiting 5 to 10 minutes sometimes lets the epoxy flow into the voids as viscosity drops slightly with initial heat; if defects persist, address the contamination source, then scrape off the layer and repour on a clean surface. On a fully cured piece, sand the affected area with medium grit (180–220), clean thoroughly with solvent, and apply a new, thin flood coat, which fills the sanded imperfections and cures smooth once the contamination source is gone.
Tracking down the actual contamination source is worth the extra ten minutes it takes, because repouring over an unresolved source just produces the same defect again in the new layer. Walk back through everything that touched the workspace in the hours before the pour — a recently applied floor wax, a new can of spray adhesive used nearby, a changed brand of hand soap, or even a new HVAC filter can each introduce a contaminant that wasn’t present on a previous, successful pour. Isolating the change is usually faster than re-cleaning everything from scratch.
Incure manufactures industrial coating and bonding epoxies where surface-energy mismatches cause the identical crawling defect on a production line as on a hobby workbench — the fix is always contamination control, never a different resin. Email Us if fisheyes keep recurring despite a documented cleaning protocol.
Related reading: how CTE mismatch causes adhesive bond failure covers a different but related substrate-interaction problem, and comparing UV-cure adhesive to epoxy for transparent bonding is useful if clarity is a project requirement alongside surface finish. Contact Our Team if a contamination source proves difficult to identify.
Visit www.incurelab.com for more information.