Sanding and filling 3D prints

This page has safety advice that hasn't yet been checked by our safety reviewer. Treat it as general guidance, and follow your game's, venue's or product's own safety rules first.

How to sand and fill the layer lines on a filament 3D print so it is smooth and ready to paint, for makers finishing printed props and armour.

When a filament printer builds a part, it lays down plastic one thin layer at a time, and those stacked lines stay visible on the surface unless you do something about them. Sanding and filling is the most common way to close that gap between a raw print and a paint-ready prop. The basic idea is to alternate between adding a filler product that settles into the valleys between layers and sanding back the high spots until the whole surface is level and smooth. Before you start, check your print for any obvious print failures: blobs, stringing, or weak layer adhesion. Snip or scrape away loose material with a hobby knife or flush cutters, working away from your fingers. Coarse sandpaper cuts quickly but leaves deep scratches, so most makers work through a series of grits, starting lower and moving progressively higher. Sanding blocks or rigid backing pads help keep flat surfaces truly flat rather than creating uneven dips from finger pressure alone. Wet-sanding with water at higher grits reduces dust and can give a finer finish. Filler products range from rattle-can sandable primers to two-part body fillers and purpose-made brush-on fillers. Each type has its own mix ratios, open working times, and recommended topcoats, so always read the product's own instructions rather than relying on a single set of numbers. Apply thin coats of filler, let each coat cure fully before sanding it back, and repeat the cycle until the layer lines disappear. Rushing this stage usually means more work later, because paint will highlight imperfections rather than hide them. Safety matters throughout this process. Sanding any plastic produces fine dust that is harmful to breathe, so work outdoors or in a well-ventilated space and wear a properly fitted respirator with the correct cartridges for dust and, if you use solvent-based fillers or primers, for organic vapours as well. Safety glasses protect your eyes from airborne particles. Two-part fillers and aerosol primers can irritate skin, so nitrile gloves are worth wearing. Younger makers should work with an adult present, and no one should sand indoors without ventilation.