Why Is My Epoxy Tumbler Fish Eye Separation Causes And Smoothing Fixes

Epoxy tumblers have become a favorite among crafters and small business owners for their glossy, durable finish and custom design potential. But even the most experienced artisans encounter issues—especially fish eye separation. This defect appears as small, circular craters or bubbles in the cured epoxy layer, often resembling fisheyes in car paint. While frustrating, understanding the root causes and applying precise corrective measures can restore your tumbler’s flawless appearance and prevent future failures.

Fish eyes are not just cosmetic flaws—they signal poor adhesion, contamination, or environmental missteps during application. Left unaddressed, they compromise both aesthetics and longevity. The good news: with proper technique, preparation, and post-cure intervention, most cases of fish eye separation can be corrected and avoided altogether.

Understanding Fish Eye Separation in Epoxy Tumblers

Fish eye separation occurs when the epoxy resin fails to spread evenly across the surface due to localized repulsion. Instead of forming a continuous film, the material pulls away from certain spots, creating dimples or craters. These defects typically emerge during the curing phase and become more pronounced after full hardening.

The primary mechanism behind this phenomenon is surface tension imbalance. Contaminants such as oils, dust, or silicone residues reduce the surface energy at specific points, causing the liquid epoxy to contract away from those areas. As the surrounding resin flows into place, it leaves behind voids that solidify into fisheyes.

While some may mistake these for air bubbles or pinholes, true fish eyes are distinct:

• They appear round with raised edges.
• They often cluster in groups rather than being randomly scattered.
• They originate from substrate-level contamination, not mixing errors.

“Fish eyes are rarely about the epoxy itself—it's almost always a surface prep failure.” — Dana Reeves, Industrial Coatings Specialist with 15+ years in resin applications.

Common Causes of Fish Eye Formation

To effectively eliminate fish eyes, you must first identify what caused them. Below are the five most frequent culprits in DIY epoxy tumbler projects:

1. Inadequate Surface Cleaning

The number one cause of fish eye separation is residual oil or grease on the stainless steel tumbler. Even fingerprints contain enough natural skin oils to disrupt epoxy adhesion. Using only water or a basic wipe is insufficient. A dedicated degreaser is essential.

2. Silicone Contamination

Silicone is notoriously difficult to remove once present. It may come from prior use of silicone-based polishes, cleaning sprays (like furniture or appliance cleaners), or even aerosols used nearby. Traces invisible to the eye can still trigger widespread fisheye formation.

Tip: Never clean your work area with products containing silicone before handling epoxy projects. Use isopropyl alcohol (IPA) instead.

3. Improper Drying After Cleaning

If the tumbler isn’t completely dry before epoxy application, moisture can create micro-repulsion zones. Water beads under the resin layer act as barriers, leading to dewetting and cratering.

4. Environmental Factors

High humidity, cold temperatures, or drafts can alter epoxy flow dynamics. Cold surfaces cause the resin to thicken prematurely, reducing its ability to self-level. Humidity increases surface moisture, exacerbating contamination risks.

5. Low-Quality or Incompatible Resin

Not all epoxy resins are formulated for vertical surfaces or food-safe coatings. Some lack the necessary surfactants to resist fish eye formation. Using outdated or improperly stored epoxy also reduces performance.

Step-by-Step Guide to Fixing Fish Eyes After Curing

Once fish eyes have formed and the epoxy has fully cured, correction requires careful sanding and recoating. Follow this timeline-based process to achieve a smooth, professional finish:

1. Assess the Damage: Inspect the tumbler under bright light. Determine whether fish eyes are shallow or deep. Shallow ones may require only light sanding; deeper ones need filling.
2. Gather Supplies: You’ll need wet/dry sandpaper (400–2000 grit), masking tape, isopropyl alcohol (90%+), lint-free cloths, fresh epoxy mix, stir sticks, and gloves.
3. Sand the Surface: Begin with 400-grit sandpaper using water as a lubricant. Sand only until fisheyes are flattened—do not grind through the epoxy layer. Progress through 600, then 1000, finishing with 1500–2000 grit for polish readiness.
4. Clean Thoroughly: Wipe away all sanded residue with IPA-soaked cloth. Repeat twice. Let dry completely.
5. Mix New Epoxy: Use a high-flow, self-leveling formula designed for tumblers. Mix slowly to avoid introducing air. Pour a thin second coat over the entire surface.
6. Apply and Rotate: Apply the new coat evenly. Place the tumbler on a rotating stand or manually rotate every few minutes for 15–20 minutes to ensure uniform coverage and prevent pooling.
7. Cure Properly: Allow 24–72 hours of undisturbed curing in a dust-free, temperature-stable environment (ideally 70–75°F).
8. Final Polish (Optional): For glass-like shine, buff with a microfiber cloth and automotive polishing compound after full cure.

“Recoating over sanded epoxy works best when the new layer bonds mechanically to the micro-textured surface. That’s why proper scuff-sanding is non-negotiable.” — Mark Lin, Resin Application Trainer at CraftPro Workshops.

Prevention Checklist: Avoid Fish Eyes Before They Start

Prevention is far easier—and cheaper—than repair. Use this checklist before every epoxy pour to minimize risk:

Tip: Perform a \"water break test\" after cleaning: spray distilled water on the tumbler. If it sheets evenly without beading, the surface is clean. Beading indicates contamination.

• ✅ Clean tumbler with acetone or 90%+ isopropyl alcohol (not rubbing alcohol with additives)
• ✅ Use lint-free wipes—never paper towels or cotton rags that shed fibers
• ✅ Wear nitrile gloves to avoid transferring skin oils during handling
• ✅ Ensure workspace is free of aerosol sprays, candles, and silicone-containing products
• ✅ Pre-warm tumbler slightly (to ~75°F) if working in cooler environments
• ✅ Mix epoxy slowly and thoroughly—avoid whipping which introduces bubbles
• ✅ Apply in a controlled environment: low dust, stable temperature, no airflow
• ✅ Let first coat cure fully before adding additional layers or glitter embeds

Do’s and Don’ts: Table Summary for Quick Reference

Do’s	Don’ts
Use 90–99% isopropyl alcohol for final wipe-down	Use household cleaners like Windex or Pledge near your workspace
Sand between coats with 600–1000 grit when reapplying	Skip sanding before a second coat—this prevents mechanical bonding
Work in a dedicated, clutter-free space	Apply epoxy in garages or kitchens where cooking oils or fumes linger
Store unused epoxy in sealed containers away from heat	Use expired or cloudy resin—pot life and adhesion degrade over time
Rotate tumblers slowly during cure to maintain even film thickness	Leave tumblers stationary—this encourages sagging and uneven distribution

Real Example: How One Crafter Fixed a Batch of 12 Flawed Tumblers

Jamie R., a small-batch epoxy artist from Austin, TX, once lost an entire client order due to sudden fish eye outbreaks. She had switched cleaning supplies temporarily, using a multi-surface cleaner she didn’t realize contained silicone. All 12 tumblers developed clusters of fisheyes within hours of pouring.

Instead of scrapping them, Jamie followed a structured recovery plan. She sanded each piece starting at 400 grit, cleaned with acetone three times, and applied a thin second coat of marine-grade epoxy known for superior wetting properties. She pre-warmed each tumbler using a hairdryer on low and rotated them manually every five minutes for 20 minutes post-pour.

Result: 11 of the 12 were fully restored. One had minor residual texture but was accepted by the client at a discount. More importantly, Jamie now tests all cleaning agents with the water break method and keeps a separate toolkit solely for epoxy work.

FAQ: Common Questions About Epoxy Fish Eyes

Can I fix fish eyes without sanding?

No—if the epoxy has fully cured, sanding is required to create a bondable surface for the new layer. Attempting to apply fresh epoxy over unsanded, contaminated areas will likely result in the same issue.

Will a torch help prevent fish eyes?

A heat gun or torch helps release trapped air bubbles but does nothing to stop fish eyes. In fact, overheating can worsen the problem by accelerating cure time and reducing leveling capacity. Prevention lies in surface prep, not flame exposure.

How long should I wait before applying a second coat?

Wait at least 24 hours for the first coat to set, but no more than 72 hours. Beyond that, the surface oxidizes and loses reactivity. If delayed longer, lightly sand and clean again before recoating.

Conclusion: Turn Mistakes Into Mastery

Fish eye separation doesn’t mean your project is ruined—it’s a learning opportunity. Every crafter encounters setbacks, but those who understand the science behind epoxy behavior turn failures into refined skills. By mastering surface preparation, controlling your environment, and knowing how to correct imperfections, you ensure consistent, stunning results.

Your next tumbler doesn’t have to suffer the same fate. Apply these insights today: clean deeper, test wider, and respect the chemistry at play. With precision and patience, your finishes will not only look professional—they’ll perform like them too.

💬 Have you overcome a tricky fish eye issue? Share your story or tip below—your experience could save another maker hours of frustration!