Wet Sanding Epoxy: Shiny Low Spots or Unfinished Scratches?

Shiny islands in wet-sanded epoxy do not all mean “keep sanding.” A patch of untouched surface may still need leveling, but a deep pit may sit below the thickness you can safely remove. Meanwhile, a uniform matte face can be ready for the next abrasive even though it looks cloudy.

This is a finishing check for fully cured, sound epoxy that is suitable for wet sanding. Its purpose is to help you decide whether to continue the current cut, refine the scratches, or stop and repair a low area.

First expose the surface you are judging

Remove contamination before evaluating sanding marks. For its cured epoxy, WEST SYSTEM describes washing away amine blush with water and an abrasive pad, followed by drying. Its final epoxy surface preparation instructions also require a clean, dry surface before the next coating. Do not interpret a washable surface film as a reason to grind deeper.

Set up runoff control before restarting. On a resin-and-wood object, water must not soak exposed end grain, open joints, underside wood or an unsealed hole. Keep the working film local and collect it immediately. Tape is a splash guard, not waterproof encapsulation. If water cannot be kept away from absorbent areas, finish those areas using another permitted process.

Wear the protection specified for the resin and abrasive, including suitable gloves for wet residue and eye protection. Water contains some debris at the work surface; it does not make the slurry harmless.

Separate a line from a depression

Rinse off the slurry, dry the face, and move a low-angle light across it. Rotate the piece if practical. Use magnification for small craters instead of repeatedly sanding to see what happens.

These observations guide the next check; they do not measure the depth of a pit or the thickness of a clear coating. If the remaining resin over artwork, pigment or a wood edge is unknown, do not sacrifice it merely to make every shiny hollow disappear.

Refine what is already level

Use a firm, flat hand block on a planar resin face. Softer support can follow a curve, but pressing it into a pit makes that depression larger instead of leveling the surrounding plane.

Wet the working face and waterproof paper with clean water. Make light overlapping strokes, keeping the support in contact without leaning on an edge. Clean away slurry as it accumulates. Before each grit change, rinse the piece, block and hands, then bring in fresh water and a clean cloth.

TotalBoat's epoxy sanding and polishing guide treats sanding haze as an intermediate condition and polishing as a separate step. Its example includes 800 grit during scratch refinement. For a process that calls for that stage, 800-grit waterproof sheets in a 100-pack provide cut-to-size material for repeated projects. That is a bulk supply option, not the amount needed for one tabletop or casting.

Do not jump to that grade to erase a deep first-cut scratch. Select the preceding and following grades from the tested resin-and-polish process, and advance only when the older pattern is gone. If a coarse line survives while the rest of the face becomes finer, polishing longer is unlikely to be the efficient correction.

A polishing test answers a different question

After the final specified abrasive stage, rinse and dry a small representative area. Polish it with the chosen compatible compound and a clean pad or cloth. Inspect after removing compound residue, not while the paste fills the scratches.

If the test becomes clear and the original lines are gone, repeat the established process on the remaining sound surface. If distinct lines reappear, return only to the abrasive stage needed to remove them. If the surface is clear but the reflection bends over a hollow, more fine sanding will not restore missing geometry.

A recoat is a separate route. Clean and prepare it to that coating's adhesion requirements rather than taking a polishing sequence as recoat preparation. Keep any compound, wax or silicone out of areas that will be bonded or coated.

At the end, collect wet residue and dry the edges, underside and any water-exposed joints before finishing. The stopping point is the surface your next operation needs—not the highest grit in the drawer and not the disappearance of every shiny spot at any cost.