How to Fix Pinholes in Resin After Sanding

Most pinholes are small air pockets that were hiding just below the cured surface. Sandpaper removes the thin layer covering them and exposes the cavities. You can repair a few holes individually or seal a larger group with a thin flood coat. The right choice depends on the number of holes, their depth, and the finish you want.

This beginner-friendly guide walks through both methods, explains which products are worth buying, and shows you how to avoid sanding straight through the repair. If bubbles are still visible before your project cures, use our guide to fix bubbles in resin before it cures instead.

How to Fix Pinholes in Resin After Sanding

To fix pinholes in resin after sanding, clean all sanding dust from the cavities, let the piece dry completely, and fill each hole with fresh mixed resin. For many scattered holes, sand the entire surface evenly and apply a thin flood coat instead. Let the repair fully cure, then level-sand and polish only if needed.

Use this quick rule to choose a repair:

• One to five isolated pinholes: fill them individually with a toothpick or fine applicator.
• Several holes in one small area: fill the area and spread a very thin resin skim coat over it.
• Pinholes scattered across the whole face: apply a full flood coat for the most even gloss.
• Deep holes that reach an inclusion: fill in two thin passes rather than one thick drop.
• Holes on a coaster edge or jewelry side: use thicker resin, UV resin, or tape as a temporary dam.

Do not polish over open pinholes and hope they disappear. Polishing compound can pack into the cavities, turn white, and make the dots more noticeable. Filling first gives you a solid surface that can be finished properly.

Why Pinholes Appear Only After You Sand Resin

A cured resin surface can hide tiny bubbles beneath a glossy skin. When you begin with coarse sandpaper, that skin is removed and the tops of the bubbles open. What looks like damage caused by sanding is often a defect that was already inside the pour.

Common causes include:

• Mixing too quickly and whipping fine air bubbles into the resin
• Pouring resin while it is cold and unusually thick
• Failing to seal porous wood, paper, flowers, or clay before pouring
• Applying too much heat, which can make resin foam or pull air from an inclusion
• Pouring a layer deeper than the manufacturer's recommended maximum
• Sanding with very coarse paper when only light leveling was necessary
• Using resin late in its working time, after it has begun to thicken

Pinholes are different from fisheyes. A pinhole is an open cavity in cured resin. A fisheye is a spot where liquid resin pulls away during a coat, often because of oil, silicone, or another contaminant. If the defects appeared during a new topcoat rather than after sanding, treat the problem as surface contamination before adding more resin.

Supplies for a Clean Pinholes Repair

You probably own many of the tools already. A basic repair kit costs about $25-$55, depending on whether you need fresh resin.

Recommended supplies include:

• Nitrile gloves: $8-$15 per box
• Safety glasses: $5-$12
• Art-grade epoxy resin: $15-$35 for a small kit
• Graduated mixing cups: $5-$10 per pack
• Toothpicks, microbrushes, or fine-tip applicators: $3-$10
• 91% isopropyl alcohol for tool and surface preparation: $4-$8
• Lint-free cloths: $5-$12
• Wet/dry sandpaper from 400 through 2000 grit: $8-$18 per assortment
• Plastic polishing compound: $8-$18
• Painter's tape: $4-$8

For a few pinholes, a slow-curing art epoxy is usually the most forgiving product because it has time to flow into each cavity. A small UV resin kit, often $15-$30 including a lamp, can work well for clear jewelry and edge repairs, but it is not ideal beneath opaque pigments or in deep holes where UV light cannot reach.

Always follow the resin manufacturer's ratio, maximum pour depth, ventilation, and protective-equipment directions. Work in a clean, ventilated area and keep uncured resin away from skin, children, and pets. Our complete resin art beginner's guide covers a safer workspace, measuring, mixing, and starter projects.

Step-by-Step Pinhole Repair

Step 1: Inspect and mark every pinhole. Wash the sanded piece with plain water if you have been wet-sanding, then allow it to dry completely. Hold it under a bright light and tilt it slowly. Side lighting creates shadows inside tiny cavities and makes them easier to see.

Circle each hole on nearby painter's tape or make a simple sketch of the surface. Do not draw directly on the resin with a permanent marker because ink can bleed into a clear repair. Check the edges as well as the center; sanding pressure often opens bubbles near corners first.

Probe suspicious dots very gently with a clean toothpick. A real pinhole catches the tip. A flat dark speck may be pigment or debris inside the resin and cannot be filled from the surface. If you discover soft, flexible, or sticky resin around the hole, stop. A fill coat will not correct an underlying cure problem. Use our resin art troubleshooting guide to identify mixing-ratio, temperature, or moisture issues before continuing.

Step 2: Remove dust from the cavities. Sanding dust prevents new resin from bonding and can leave a pale ring inside clear pieces. Use a clean, soft brush or oil-free compressed air to lift dust from each hole. Keep an air can upright so it does not spray cold propellant onto the project.

Next, wipe the surface lightly with a lint-free cloth dampened with 91% isopropyl alcohol, provided your resin manufacturer allows it. Do not flood the holes. Let the alcohol evaporate fully before mixing fresh resin. Water, alcohol, or cleaning residue trapped in a cavity can create cloudiness or another bubble.

Avoid household glass cleaner, furniture polish, acetone, oily tack cloths, and silicone-based products. They may leave residue that causes the repair resin to separate. Once clean, handle the piece only by its edges while wearing gloves.

Step 3: Fill a few pinholes individually. For isolated holes, mix the smallest practical batch of resin using the exact ratio printed on the label. Stir slowly for the full recommended time, scraping the cup walls and bottom. If the brand recommends transferring to a second cup and stirring again, do that; unmixed resin from the first cup can leave a soft repair.

Let the mixture rest for two or three minutes. Dip the tip of a toothpick or microbrush into the resin and touch it to the inside wall of a pinhole. Dragging resin along the wall helps displace trapped air rather than sealing air under a drop.

Slightly overfill the cavity because resin can settle as it levels. For a deep pinhole, apply a partial fill, let it cure, and add a second pass. This reduces the chance of trapping another bubble. Check the repair after 10 minutes and pop any surface bubble with a clean toothpick.

For holes on a vertical edge, place painter's tape tightly beneath the repair to create a tiny dam. Choose a resin near the end of its working window, when it has thickened slightly but still flows. Remove the tape at the stage recommended by the manufacturer, or after curing if your test piece shows it releases cleanly.

Step 4: Use a thin flood coat for many pinholes. When pinholes cover a broad area, individual dots can leave a bumpy finish. A thin flood coat fills the openings and restores an even gloss in one step.

First, sand the complete face uniformly with about 320- or 400-grit paper. The surface should look evenly matte with no shiny islands. Round any razor-sharp edge slightly so the fresh resin can hold onto it instead of pulling away. Clean and dry the piece carefully.

Level the worktable, tape the underside edges to catch drips, and raise the piece on small blocks. Mix enough coating resin for the manufacturer's stated coverage. Spread a thin, continuous layer with a silicone tool or gloved finger. Work the resin across the pinholes from more than one direction so it enters each cavity.

Pass a heat gun quickly above the surface only if the product permits it. Too much heat can make the coat thin, run off the edges, or create fresh pinholes. Cover the piece with a clean dust cover and leave it undisturbed for the full cure time. A flood coat usually produces a better finish than dozens of separate dots, but it changes the dimensions slightly. On fitted lids, dominoes, dice, or precision jewelry components, spot filling may preserve the shape better.

Step 5: Sand the repair without reopening it. If the filled dots stand above the surface, wait until the resin reaches a full hard cure before leveling them. Beginning too early can pull the repair from the hole or smear soft resin across the piece. Cure time may be 24 to 72 hours or longer, so use the product instructions rather than the clock alone.

Wet-sand gently with a firm, flat backing block. Start around 600 grit for a small raised dot; use 400 grit only when substantial leveling is required. Move through 800, 1000, 1500, and 2000 grit without skipping large jumps. Rinse the piece and sandpaper often.

Stop as soon as the repair is level. Aggressive sanding can cut through the fill and reopen the same cavity. If that happens, clean the hole and repeat the spot-fill process instead of pressing harder. You can skip sanding entirely if a flood coat cured smooth and glossy. Extra sanding adds work and creates another opportunity to expose bubbles beneath the new surface.

Step 6: Polish the repaired resin. After sanding through fine grits, dry the piece and inspect it under side lighting. The surface should have an even haze with no deep scratches. Apply a small amount of plastic or resin polishing compound to a microfiber cloth and buff in overlapping circles.

A small rotary tool can speed up polishing jewelry, but use the lowest practical speed and light pressure. Heat from a fast polishing wheel can soften resin or create waves. Keep the wheel moving and pause if the piece feels warm. For a satin project, you may prefer the uniform finish left by 1000- or 1500-grit paper. For a glass-like face, continue to 2000 or 3000 grit before polishing. The repair should become nearly invisible when the fill resin matches the original resin's clarity and color.

How to Prevent Pinholes During Your Next Pour

Prevention begins before the resin reaches the mold. Warm sealed resin bottles in lukewarm water if the manufacturer permits it, then dry them before opening. Slightly warmer resin flows more easily and releases bubbles faster, but hot resin cures quickly and can overheat.

Measure accurately, stir slowly, and pour in a thin stream close to the mold. Seal porous inclusions with a compatible clear coat before embedding them. Brush a thin resin layer into detailed mold corners before filling the rest of the cavity.

Use heat sparingly and early in the working time. A quick pass can pop surface bubbles; repeated torching can damage a silicone mold and introduce new defects. Pour within the product's depth limit and cure the piece at a stable room temperature on a level surface.

Finally, begin sanding with the finest grit that can accomplish the job. If the surface only needs light scuffing before a topcoat, 400 grit may be enough. Starting at 80 or 120 grit removes material rapidly and can expose bubbles that would otherwise remain safely beneath the surface.

Frequently Asked Questions

Can I fill resin pinholes with UV resin?

Yes, UV resin is useful for small, shallow pinholes in clear or translucent jewelry because it cures on demand. Apply a tiny amount, make sure no air remains, and expose it for the lamp time specified by the manufacturer. Do not rely on UV resin inside deep cavities, beneath opaque pigment, or anywhere the curing light cannot reach.

Will polishing compound fill pinholes in resin?

No. Polishing compound is designed to refine fine scratches, not repair cavities. It can collect inside pinholes and dry white. Clean the holes, fill them with compatible resin, let the repair cure, and then polish the solid surface.

Can I apply resin over a sanded surface?

Yes. A uniformly sanded surface gives fresh epoxy a mechanical bond. Remove every trace of sanding dust, moisture, oil, and polishing compound before recoating. Follow the resin brand's preparation directions because recoat windows and recommended grits vary.

Why did my new resin coat create more pinholes?

The surface may have been contaminated, the old pinholes may still have contained dust or air, or the fresh coat may have been overheated. Porous material can also keep releasing air into a new coat. Clean thoroughly, seal porous areas, spread the coat from multiple directions, and use only brief heat passes.

Learning how to fix pinholes in resin after sanding turns a frustrating surprise into a manageable finishing step. Clean every cavity carefully, spot-fill isolated holes, use a thin flood coat for widespread defects, and allow the repair to cure fully before leveling it.

Work slowly during the final sanding stages. The goal is to blend the repair, not remove it. With accurate mixing, a clean surface, and gentle polishing, most pinholes disappear into a smooth finish—and your resin project can look every bit as polished as you originally planned.