3D Printing Surface Processes: Sanding, Primer and Paint

3D Printing Surface Processes: Sanding, Primer and Paint FDM print layer lines may not affect the part's function but reduce its visual quality. With a few simple steps, the surface can look like it came out of a mold. 1. Preparation and Cleaning After printing is completed, support structures are first removed with a sharp hobby knife. Oil and dust remaining on the surface prevent paint adhesion; the part should be washed with warm soapy water and completely dried. 2. Sanding Sequence Sequence is important; move from coarse sanding to fine sanding. - 120–180 grit: Evident layer lines and support points are smoothed. - 320–400 grit: Makes the surface smooth before primer. - 600–800 grit: Used for final smoothing after primer. Wet sanding reduces dust formation and gives a smoother result. 3. Primer Application Filler primer fills remaining micro scratches and increases paint adhesion to the surface. It should be applied in thin layers, waiting for each layer to cure. After the primer dries, light sanding with 600–800 grit ensures a smooth surface after painting. 4. Paint Selection and Application - Acrylic spray: Easy to find, dries quickly; suitable for indoor parts. - Polyurethane (PU) spray: More durable and full coating; good for outdoor and frequently used parts. - Brush paint: Practical for small details and touch-ups; risk of leaving marks is high. Paint should be applied in thin layers from a distance of 20–25 cm. A thick single layer causes runs and drips. 5. Protective Coating Matte or gloss varnish delays the wear of the paint and yellowing from UV. For parts used outdoors, varnish is almost mandatory. Common Mistakes - Painting without cleaning: Due to dust and oil, paint bubbles or peels. - Skipping primer after coarse sanding: Layer lines remain visible under paint. - Single thick coat: Surface runs, curing takes longer, texture is ruined. - Keeping PLA at high temperature: PLA softens around 60 °C; curing after painting with an oven is not suitable. Material-Specific Notes - Painting with PLA gives the easiest result. - Due to PETG's low surface energy, primer use is even more important. - Since TPU is flexible, a flexible primer/paint should be preferred. - ASA/ABS can be smoothed with acetone vapor; however, this method requires good ventilation. Specifying your surface quality expectations at the start of the order ensures the production plan is set up correctly. With PrintFlow TR, you can add your finishing expectations to the quote and track the production process transparently.