How to Prepare and Paint 3D Printed Parts

Introduction

One stage in the finishing workflow is critical for transforming 3D prints into a professional-looking result. Many beginners overlook it, but experienced model makers always include it. It simplifies painting and ensures a smooth, high-quality surface. That essential step is priming.

Applying a final paint layer gives a model depth and refinement. However, paint does not conceal imperfections. Without proper preparation, small layer steps, support scars, or polygonal facets from the print will remain visible. Depending on the printing method, layer lines may also be obvious. If you’re aiming for a high-end finish, priming is non-negotiable.

Priming creates a clean, uniform surface ready for paint. The typical grey tone helps reveal flaws so they can be sanded or filled. It also improves paint adhesion and results in a more professional finish—particularly for glossy coatings.

Sanding & Priming

Before applying primer, the surface must be smooth. While primer can fill tiny imperfections, thin paint layers will still reveal underlying detail.

For Resin prints, this means removing support marks. For PLA FDM prints, sanding the entire surface is often necessary to eliminate visible layer lines. Heavy primer can substitute for sanding, but it may obscure fine detail.

Once sanding is complete and the first primer coat is applied, inspect the model again. Primer’s matte finish makes flaws easy to spot under good lighting. Apply a final primer coat and allow it to dry according to the manufacturer’s instructions. A light polish afterward can further improve the surface.

Sanding & Priming Steps

1.      Sand down support marks and layer lines.

Use a rotary tool, hand file, or around 220-grit sandpaper to carefully remove support remnants and layer lines.

2.     Sand and smooth the surface.

Start with 220–320 grit sandpaper and gently smooth the entire model. Follow with finer grits (400–600) to refine the finish.

3.     Wash the surface to remove dust.

Clean the model with water and a soft brush. Distilled or deionized water can help avoid residue marks.

4.     Wipe down with a tack cloth.

Wearing gloves, wipe the model with long, consistent strokes. Ensure you reach into small crevices.

5.     Mix the primer.

Swirl the can gently for 2–3 minutes instead of shaking. This prevents bubbles. You should hear the internal mixing ball moving freely once ready.

6.     Apply the first primer coat.

Spray in short bursts from 6–8 inches away. Begin and end each pass off the model. Rotate the part and keep layers thin to avoid pooling.

7.     Inspect the surface.

Check for imperfections. If needed, sand lightly with fine (>600 grit) paper and clean before reapplying primer.

8.     Apply the final primer coat.

Spray another thin, even layer. Stop once coverage is opaque to avoid losing fine detail.

Sanding & Priming Tool Checklist

• Primer

• Rotary tool

• Hand files

• Sandpaper or flexible sanding sheets (220/320, 400/600 grit)

• Water

• Soft brush

• Tack cloth

• Wooden painting block

• Drill and drill bits

• Dowels for holding parts

• Safety gear: gloves and mask

Painting

Once primed, spray painting becomes straightforward with proper technique. For a glossy finish, build up several thin, even coats. This layering creates depth and richness in colour.

Hold the spray can close to the model and move quickly to achieve thin coats. Rotate the model to maintain even coverage. Between coats, lightly polish the surface to keep it smooth—this is key for achieving a high-gloss final clearcoat.

For deeper colour, apply an undercoat. This base layer hides the primer’s neutral tone. Typically, 2–3 thin coats are sufficient. Black works well under dark colours, while white suits lighter tones.

Masking

Masking allows you to preserve specific areas between paint layers. Avoid leaving general-purpose masking tape on the model for extended periods (more than a few days).

Applying Final Top Coat Colour (optional)

After masking, apply the topcoat. Think of this as a translucent layer over the base colour. Thinner coats allow the undercoat to influence the final tone. Pause briefly between coats to assess colour depth.

Applying Clear Coat

Once satisfied with the colour, apply 1–2 thin layers of clearcoat. A properly polished surface will allow the clearcoat to level out into a smooth, glossy finish. For added protection, you can polish with ultra-fine cloths or apply carnauba wax.

Drying Time

Allow the model to dry thoroughly after painting. While there’s no strict rule, letting it cure for about a week ensures the paint fully hardens. If handling sooner, wear gloves and be gentle to avoid damage.

Painting Steps

1.      Start with a primed part.

Ensure sanding and priming are complete.

2.     Buff and polish the surface.

Use buffing sticks (skip the coarsest level) and finish with polishing for a smooth, glossy base.

3.     Remove dust.

Wipe the model with a tack cloth using light, consistent strokes.

4.     Prepare for painting.

Wear protective gear. Mix the paint by gently swirling the can for 2–3 minutes.

5.     Apply the undercoat.

Spray evenly from about 6 inches away, starting and ending off the model. Build up 2–4 thin layers, allowing 20–30 minutes drying time between coats.

6.     Polish between layers.

Lightly sand or polish between coats to refine the surface.

7.      Mask selected areas.

Cut and apply masking tape carefully, pressing edges firmly to prevent paint bleed.

8.     Apply the topcoat (optional).

Use 1–2 light coats for subtle colour variation or blending.

9.     Finish with clearcoat.

Apply 1–2 thin layers for protection and desired finish (gloss or matte).

Painting Tool Checklist

• Paint (undercoat and topcoat colours)

• Buffing sticks

• Fibre-backed polishing paper

• Tack cloth

• Masking tape

• Clearcoat

• Safety gear: gloves and mask