Smoothing epoxy resin is a multi-stage process that moves from coarse sanding to fine sanding to polishing, with each step erasing the scratches left by the previous one. The full sequence can take a surface from rough and uneven to glass-clear, but rushing any stage or skipping grits will leave visible marks that are difficult to fix later. Here’s how to do it right.
Wait for a Full Cure First
Most epoxy resins need 24 to 48 hours of curing before they’re hard enough to sand. Thicker pours can take up to 7 days. If you start too early, the resin will gum up your sandpaper and tear rather than sand cleanly. Check your specific product’s instructions, but there’s also a simple test: press your fingernail into an inconspicuous spot. If it leaves an indent, wait longer. The surface should feel hard like plastic with no give at all.
If your sandpaper starts clogging with gummy material during sanding, stop immediately. Either the resin hasn’t fully cured or you’re generating too much heat from friction. Let it sit longer before trying again.
The Sanding Grit Progression
Sanding epoxy is about working through progressively finer grits, each one replacing the deeper scratches from the last with shallower ones. The general sequence looks like this:
- 60 to 80 grit: Only for removing large bumps, drips, or major unevenness. Skip this if your surface is relatively flat.
- 120 to 150 grit: The typical starting point for most projects. This levels the surface and removes visible imperfections.
- 200 to 400 grit: Smooths out the scratches left by the coarser paper and prepares the surface for fine finishing.
- 600 to 2000 grit: Creates the refined, uniform surface needed before polishing.
Don’t skip grits. Jumping from 120 straight to 600, for example, means the fine paper has to do the work of removing deep scratches it wasn’t designed for. You’ll spend more time, wear out more sandpaper, and likely end up with an uneven result. Move through each step until the entire surface has a consistent, uniform haze at that grit level before stepping up.
Dry Sanding vs. Wet Sanding
Dry sanding works best for the early stages: leveling uneven surfaces, knocking down high spots, and preparing epoxy to receive another coat. It removes material quickly but produces a lot of fine dust and generates more heat, which can clog your paper faster.
Wet sanding uses water as a lubricant and coolant. It’s the better choice for fine finishing work from around 400 grit onward. The water flushes away particles so they don’t scratch the surface, reduces heat buildup, and virtually eliminates airborne dust. Keep the surface wet by periodically dripping or spraying water as you work. You’ll feel the sandpaper glide more smoothly, and the surface will develop a consistent, milky haze rather than rough scratches.
Sanding Technique That Actually Matters
Use a straight-line crossing pattern rather than circular motions. Sand in one direction for a given grit (left to right, for example), then switch to an up-and-down motion for the next grit. This makes it easy to see when you’ve fully replaced the previous grit’s scratch pattern, since the new scratches will run perpendicular to the old ones. Wrap your sandpaper around a flat foam sanding block to distribute pressure evenly. Uneven pressure creates dips and waves in the surface that become painfully obvious once you polish.
If you’re using a random orbital sander to speed things up, keep it moving in smooth, sweeping passes. Don’t let it sit in one spot, as concentrated heat can soften or cloud the resin.
Polishing to a Clear, Glossy Finish
After sanding through your highest grit (1500 to 2000), the surface will look uniformly hazy. Polishing is what brings back the clarity and gloss. Apply a medium-cut polishing compound to a foam or microfiber pad and work it across the surface in overlapping passes. You can do this by hand or with a buffing wheel or orbital polisher.
Wool pads are more aggressive and good for the first polishing pass, especially if there are remaining fine scratches. They provide more cutting power but can leave faint swirl marks. Follow up with a softer foam pad and a finer polishing compound to remove those swirls and bring up the final shine. Softer, less dense foam pads are ideal for this last step.
If you’re using a powered buffer, keep the speed moderate. Experts recommend staying in a range that provides enough friction to cut without overheating the surface. Too fast melts or scorches the resin; too slow won’t do anything. For random orbital sanders, stay at or below 3,500 RPM. Keep the tool moving at all times.
Going Beyond: Ultra-Fine Abrasive Systems
For a true mirror finish, especially on clear resin pieces like jewelry, river tables, or art, standard sandpaper and polishing compound may not be enough. Micro-mesh abrasive sheets range from 1500 all the way up to 12000 grit. Starting at around 2400 and working through the series to 12000 will produce a high-reflective surface that looks like glass. High gloss typically appears between the 6000 and 12000 steps.
These sheets work best with water and a few drops of dish detergent as a lubricant, which reduces the effort needed and produces a slightly better result. Use the same straight-line crossing pattern, alternating direction with each grit change. You can use them by hand wrapped around a foam block or on a random orbital sander at low speed.
Skipping the Sanding: The Flood Coat Method
If your surface has minor imperfections and you’d rather not sand through multiple grits, applying a fresh flood coat of epoxy is an alternative. A thin self-leveling pour fills in small pits, scratches, and unevenness and cures to a naturally glossy surface.
To do this properly, the existing cured epoxy needs to be lightly scuffed with 220-grit sandpaper so the new layer bonds mechanically. Clean the surface thoroughly with acetone and wipe dry with shop towels. Don’t use tack cloths, as they can leave fibers behind. Make sure your work surface is perfectly level, since the epoxy will flow to the lowest point. Apply the flood coat at around 1/8 inch thick using a notched plastic trowel to spread it evenly, keeping total thickness under 1/4 inch per pour. Placing painter’s tape along the underside edges of your piece catches drips and saves significant sanding later.
Sealing the edges and sides of porous materials like wood before the flood coat prevents trapped air from escaping through the wet epoxy and creating bubbles. Two to three thin seal coats may be needed depending on the material.
Fixing Fish-Eyes and Pitting
Small craters or “fish-eyes” in cured epoxy are typically caused by one of three things. Surface contamination is the most common culprit: silicone-based polishes, uncured stains, or sealers that haven’t fully dried will repel epoxy and cause it to pull away in small circles. The fix is to let the cured epoxy harden completely, sand it flat with 120 to 150 grit, and recoat after ensuring the underlying contamination has been removed or has fully cured.
Pouring too thin also causes pitting, since the epoxy doesn’t have enough mass to level itself and fill low spots. If the craters are minimal, you can use a squeegee to fill just those areas with fresh epoxy, then sand flat once cured. For widespread pitting, sand the entire surface level with 120 to 150 grit and pour a proper-thickness flood coat.
A surface that’s too smooth (from overly fine sanding before a recoat) can also cause fish-eyes because the new layer can’t grip. Stick to 120 to 150 grit when preparing for an additional coat rather than going finer.
Safety While Sanding Resin
Epoxy sanding dust is not something you want to breathe or get on your skin. Even after the surface feels hard, the curing process may not be fully complete for up to two weeks. Until then, sanding dust can contain unreacted chemical components that are hazardous if inhaled or if they settle on exposed skin.
Wear a cartridge-type respirator with organic vapor cartridges, not a simple dust mask, especially when sanding recently applied epoxy. Nitrile gloves protect your hands, and safety goggles keep fine particles out of your eyes. A long-sleeved shirt or coverall prevents dust from contacting your skin. Wet sanding at the finer grits naturally reduces airborne particles, which is one more reason to switch to wet methods as soon as your grit progression allows it.