What's inside
As an Amazon Associate I earn from qualifying purchases. This post may contain affiliate links at no extra cost to you.
Fish eyes are small, round craters that appear when a wet finish pulls away from contaminated spots on a wood surface. They may look like tiny dimples, pinholes, or circular openings with a raised ring around them. The usual cause is silicone, wax, oil, polish, or another substance with lower surface tension than the finish. The defect can occur in polyurethane, lacquer, varnish, epoxy, paint, and waterborne topcoats.
The important point is that fish eyes are usually a surface-preparation problem, not a sanding problem. Adding more finish often makes the craters larger or creates new ones.
Identify the Problem Before You Sand
True fish eyes form while the finish is wet. The coating retreats from a contaminated spot, leaving a circular crater. They are commonly scattered across the surface, although they can be concentrated where someone used furniture polish, aerosol cleaner, paste wax, or silicone-containing oil.
Other defects can look similar. Pinholes are usually tiny openings caused by trapped air or solvent. Dust nibs are raised particles, not craters. Crawling is a broader separation pattern where the coating pulls into irregular islands. If the surface was wet-sanded with a soapy solution, soap residue can also cause poor wetting.
| Defect | What it looks like | Likely response |
|---|---|---|
| Fish eyes | Round craters with a clean or raised edge | Remove contamination, then refinish |
| Dust nibs | Small raised bumps | Let dry, level-sand, and recoat |
| Pinholes | Tiny holes without a distinct ring | Use thinner coats and improve brushing or spraying technique |
| Blushing | Milky or cloudy appearance | Control humidity, temperature, and solvent evaporation |
Stop Applying Finish and Let It Dry
If fish eyes appear during application, stop immediately. Do not brush back and forth trying to close them. That spreads the contamination and can leave brush marks or ripples.
Let the coating dry according to its label. A waterborne finish may be ready to sand in a few hours, while oil-based polyurethane can require 12 to 24 hours or more. If the film still feels soft or gums up sandpaper, it is not ready. Sanding too soon creates a larger repair area and can smear contaminated finish into the wood.
Remove the Contamination
For a small repair, wash the cured surface with a clean cloth and a suitable surface cleaner. Use the finish manufacturer’s recommended cleaner when possible. A mild detergent solution can remove ordinary grease, but it will not reliably remove silicone or wax. Follow with clean water if the cleaner requires rinsing, then allow the wood to dry completely.
For heavier contamination, use a dedicated wood finishing surface cleaner. Test it on an inconspicuous area first. Some strong solvents soften existing finishes, dissolve stain, or leave their own residue. Use fresh, lint-free rags and change them often; wiping with the same dirty rag only moves oil around.
Do not assume that denatured alcohol, mineral spirits, or acetone are interchangeable. Alcohol can damage some waterborne or shellac finishes, while acetone can attack many coatings quickly. Mineral spirits may dissolve oily residue but can also leave a slow-evaporating film if used carelessly. Ventilate the area and follow the solvent’s safety instructions.
Sand the Surface Without Spreading the Problem
Once the finish is hard, level the affected area with a sanding block. Start with 320-grit paper for a thin topcoat. If the craters are deep or the finish is thick, use 220 grit, then progress through 320 and 400 grit. Sand only until the crater edges disappear; sanding through to bare wood over a large area creates an unnecessary color and sheen mismatch.
Remove sanding dust with a vacuum and a clean, dry microfiber cloth. Avoid tack cloths that contain wax or oily resins. If the wood is bare after sanding, clean it and let it dry before applying a compatible sealer or finish. A thin first coat of dewaxed shellac can sometimes isolate persistent contamination, but it is not a guaranteed cure and must be compatible with the topcoat.
Choose Whether to Use a Fish-Eye Additive
For isolated defects, removing the contamination is the better repair. If the entire surface or a large batch of finish is affected, a manufacturer-approved fish-eye control additive may allow the coating to flow over minor contamination. These additives lower surface tension, which is why they work.
Use only the amount listed on the label. Too much can cause poor adhesion, excessive leveling, a permanently contaminated surface, or problems when the piece is refinished later. Additives also do not remove the silicone; they only help the finish tolerate it. Mix a small test batch first.
| Approach | Best use | Trade-off |
|---|---|---|
| Clean and sand | A few craters or a repairable panel | Most reliable, but requires extra prep |
| Fish-eye control additive | Widespread contamination or production work | Fast, but can complicate future refinishing |
| Strip and refinish | Severe contamination through several coats | Most work, but gives the cleanest reset |
Apply the Repair Coat Correctly
Use a clean brush, pad, or spray setup. Apply a thin, even coat rather than flooding the craters with extra material. Heavy coats stay wet longer, sag more easily, and give contamination more time to create defects. For brushing, lightly tip off the finish in one direction and stop touching it once it starts to set.
Keep the workspace between roughly 65 and 80 degrees Fahrenheit, with moderate humidity and low dust. Avoid applying finish over a cold panel; condensation or slow drying can worsen wetting problems. Make sure the product is thoroughly mixed, but do not shake a finish that creates bubbles.
After the repaired coat dries, inspect it under angled light. If it is smooth, continue with the next coat. If new fish eyes appear, stop and reassess the contamination source rather than adding more coats. For final leveling, use 320- and 400-grit wet-dry sandpaper with the lubricant recommended for that finish.
Prevent Future Fish Eyes
Keep silicone furniture polish, spray wax, oily hand creams, and household cleaners away from the finishing area. Use separate rags for cleaning and finishing. Clean the workbench, vacuum dust, and avoid compressed air from an oily compressor. If you spray, inspect hoses, filters, and the air separator for compressor oil.
Always test the complete process on scrap from the same wood species. Include the same stain, sealer, and topcoat. A five-minute test can reveal contamination that would otherwise ruin a tabletop after several hours of work.
If fish eyes continue after cleaning and sanding, the cheapest dependable option is usually to strip the affected finish and start again with isolated tools and rags. Additives are useful for controlled production work, but they are not a substitute for a clean surface.
0 Comments