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I Can't Believe It's Printed!

Best Paint for Plastic (PLA, ABS, PETG, Nylon)

Picture of Lamin Kivelä
by Lamin Kivelä
Jul 31, 2019
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When it comes to finishing 3D prints, elementary school arts and crafts ain't gonna cut it. Step up your game with this guide on the best paint for plastic.

Best Paint for Plastic Why Paint and Finish a 3D Print?

You can come a long way with ordinary spray cans
You can come a long way with ordinary spray cans. Source: MakerBot

Despite multi-material extruders and the stunning array of filament colors, you may find yourself looking to paint some of your 3D prints. The most common reason to do this is to improve how the print looks, especially if you’ve got an FDM 3D print, where the model is built using layers of filament. The technique creates a surface of characteristic lines along the Z-axis of your model.

When finishing your model, the small cavities between the layers get sanded down, filled in, or both. The result is a smoother surface. Painting can also help protect the model from the environment.

This article is divided into two parts: The first will take you through the different methods of painting your 3D print and the second will (hopefully) answer all your nitty-gritty questions about painting and how to do it best. Read on to perfect your prints with paint!

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Best Paint for Plastic Primer: Paint's Best Friend

Priming is the first step to getting paint to stick
Priming is the first step to getting paint to stick. Source: Formlabs / YouTube

Priming a model imrpoves paint adhesion. Thus, with every painting method (except dyeing nylon), using primer is a good idea. We believe a spray primer is easiest to get good results. The process of using a primer is very straightforward:

  1. Clean and sand your model.
  2. Apply the primer in thin, even coats.
  3. Sand after the first and last coats to get a smooth surface.
  4. Let each coat dry according to the instructions that come with the primer.
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Best Paint for Plastic Method 1: Painting with a Paintbrush

Using acrylic paint and a paintbrush
Using acrylic paint and a paintbrush. Source: Make Anything / YouTube

Best for: PLA, ABS, PETG

If you paint your model with a paintbrush, it is easy to get a handmade look.

Try out a few paintbrushes first because it’s easier to get a good result with a brush that you are comfortable with. We often find ourselves using only 1 or 2 different flat brushes.

The Paintbrush

  1. Choose a quality brush that’s stiff enough to handle the viscosity of the paint you have chosen to work with.
  2. Experiment with different bristle types and handle shapes to find what works for you.
  3. Pause your paint job to clean the brush as soon as the paint starts to dry. Of course, you should also clean it after each use. You do not want to leave any paint drying anywhere on the bristles.
  4. Always store your brush after cleaning it and rest it on the handle, not the bristles.

The right paintbrush can move the paint where you want it to go on the surface without dragging it around too much.

The Paint

When it comes to painting with a paintbrush, you’re going to want to stick to acrylic paints.

Application

  1. Clean and sand your model.
  2. Apply the paint in thin, even coats.
  3. Allow it to dry between coats.
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Best Paint for Plastic Method 2: Painting with Aerosol

Spray painting a 3D model.
Spray painting a 3D model. Source: 3dwithus.com

Best for: PLA, ABS, PETG

For a more uniform look, painting with spray paint can give good results.

The Spraycan

  1. Some brands offer nozzles with different characteristics.
  2. Shake the can before use, for as long as the manufacturer recommends. You want the paint to come out as evenly as possible.
  3. Keep the nozzle clean. Usually this is done by spraying some with the can upside-down at the end of each session.
  4. Keep the can away from open flames and store in a cool place. (It is a pressurised container.)

The Paint

Searching for spray paint, you’ll find that there are many varieties available. If you’re aiming for a particular color, be wary of RAL, CMYK, and RGB numbers.

Application

  1. Clean and sand your model.
  2. Start spraying with the stream pointing slightly outside the edge of the object you want to paint.
  3. Apply the paint by spraying the surface you want to paint in slow, even strokes.
  4. Stop spraying with the stream pointing slightly outside the object you want to paint.
  5. Allow the paint to dry between coats.
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Best Paint for Plastic Method 3: Dyeing (Nylon Only)

A nylon print after a nice little swim
A nylon print after a nice little swim. Source: MatterHackers / YouTube

Works best with: Nylon

Instead of trying to get paint to stick on the surface of your FDM 3D printed nylon, we recommend dyeing instead. Note that this will not work at all on other materials. Although PLA is hydroscopic and will absorb some amount of water from its surroundings, it can’t be colored by dyeing. ABS and PETG don’t belong here either – this is a nylon special.

To let the dyed color show as much as possible in your nylon 3D print, you want to use a translucent or white nylon filament when 3D printing. Darker nylon filaments are also possible to dye, but the color will be much less pronounced.

The Dye

You have many brands of dye to choose from, but MatterHackers, for example, recommends Rit DyeMore. As long as the dye is made for synthetic fabric, like nylon, you should be fine.

The Dyeing Process

Because nylon is very hydroscopic, it absorbs water even from the open air. That’s why you should always dry your nylon filament before 3D printing. We recommend that you dye the finished model, instead of the unprinted material.

Applying

Read the manufacturer’s instructions for the dye you have chosen. In short, the method is very simple:

  1. Clean your model. If sanding, keep in mind that dyeing does not cover any scratches or marks on the surface of your model. Everything will be visible even after dyeing.
  2. Mix the dye with water and heat it in a pot.
  3. Use a thermometer to keep track of the dye temperature. Follow the manufacturer’s instructions, but keep the temperature below your filaments heat deflection temperature.
  4. Tie a weight to your 3D print and submerge it in the pot with the dye.
  5. After dyeing, rinse well in a bath of cool water.

To make sure you get the right color, you may want to try dyeing some test prints before the actual print job.

Learn more about how to dye your nylon print from MatterHackers, who have a handy guide on the topic.

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Best Paint for Plastic What Makes Paint Stick?

A flatter profile on the surface means more wetting, and better adhesion.
A flatter profile on the surface means more wetting, and better adhesion. Source: Krüss

Probably the most important factor to make the paint, or liquid of your choice, stick to a solid surface is the difference in surface energy between the liquid and solid. The one with the highest surface tension always wins. (Surface tension has its own unit of measurement called dynes, or dynes per square cm.)

The rule of thumb is that the surface tension of the paint has to be at least 10 units lower than that of the solid for good adhesion. That indicates we have a liquid with a high ability to wet the solid, and wetting is what we want.

A Neat Trick

To get a hint of how well it wets the surface you want to paint, take notice of what shape a drop of liquid forms on the solid surface:

  1. Apply a drop of paint or liquid on the surface you want to finish.
  2. If the liquid forms a ball, it has too much surface tension to effectively wet the object, and the solid will not be able to “pull” the liquid onto itself.
  3. If the liquid spreads out on the surface, forming something more like a lens, the wetting is better.
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Best Paint for Plastic Can You Paint All Plastics?

Not all prints need extra color
Not all prints need extra color! Source: ChaosCoreTech / Thingiverse

Painting FDM 3D printed models made from PLA and ABS is straightforward.

PETG, however, may be harder to paint with a durable result, but the same preparations apply as with PLA and ABS. If you really need the color to stick, we would suggest printing your PETG model in the color you want, and leave it at that.

When we’re talking about FDM 3D printed nylon, it becomes much harder to get liquids like paint to stick to the surface. It is possible to paint onto nylon, but it requires some kind of heat treating to maximize the surface tension and make it possible for the paint to wet. This is often done with an open flame or plasma – not something you want to do in a home environment. We believe dyeing, as described earlier, is far better for nylon.

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Best Paint for Plastic Planning Before 3D Printing

Make finishing your print job easier by planning even before you start printing.
Make finishing your print job easier by planning even before you start printing. Source: Ultimaker

Make finishing and painting a lot easier before 3D printing your model by taking these considerations in mind:

  • A lower 3D print resolution saves time in printing but adds time in finishing.
  • Consider the geometry of your model. Your tools have to reach where you want to sand or paint.
  • Do the smallest details need sanding, priming or both? If so, can they handle it without breaking?
  • If dimensional accuracy is important for some parts of your 3D model, you may have to take that into account when modelling. Add material to be sanded down to the right dimensions, or shrink some measurements to make room for primer and paint.
  • Primer and paint adds thickness and can totally obscure smaller details on your model.
  • Sanding removes material and makes your model weaker.
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Best Paint for Plastic Prepare for Better Adhesion

Nitrile gloves protect the surface you want to paint and your hands.
Nitrile gloves protect the surface you want to paint and your hands. Source: Amazon

Some easy steps to enhance paint adhesion:

  • Wear clean gloves when handling your 3D-print, to protect your skin from chemicals and the surface of your model from from skin oils.
  • Remove contaminations before sanding, you do not want to sand dirt into your model. Isopropyl alcohol (rubbing alcohol) on a lint-free, soft rag often works well for this.
  • Use a regular vacuum cleaner, with a soft and clean brush nozzle, to remove the sanding particles.
  • Sand away any new roughness added by the primer. Always try chemicals like paint, cleaning solvents, sanding, or other materials and methods on a test piece before moving on to the actual model you want to work on.

Feature image source: All3DP

License: The text of "Best Paint for Plastic (PLA, ABS, PETG, Nylon)" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.

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