3D printing is becoming a mainstream hobby and an important new manufacturing process for professionals. However, with its increase in popularity, many beginners are quickly disappointed with their first models because they aren’t ready for the display case.
The truth is most of those highly detailed polished models you see online are polished through a post-production process. Having a successful print is worth celebrating, especially if you’re just starting out, but it’s far from having a finished product. So you need to learn and master the art of finishing your 3D print. But that doesn’t mean you should be neglecting your printing skills. In fact, you need a really clean print because post-production looks as good as the foundation you’re working with.
To create a polished piece you first need to explore the art of painting 3D models. When it comes to 3D prints, we can’t rely on our kindergarten-level arts and crafts skills. Now let’s dive into this guide on what paint to use for 3D prints and how to finish your models the right way.
Why paint your 3D print?
While you can use multiple types of filaments in different colors to create a decent looking model, the paint will still be superior for a lot of designs. The main reason is of course aesthetics. Looks are important, especially if you’re using an FDM printer because it usually leaves tiny cavities between the layers.
Painting doesn’t involve just slapping a coat of paint over the rough print. It includes sanding the rough surfaces and filling in the small cracks and crevices. The paint is a decorative element that offers some additional protection from our environment. So let’s start learning about the painting process by starting with the primer.
Priming your model
Before you start painting your 3D print, you should sand it to refine all the hard edges and imperfections and to create a smooth surface. Use a few different grains and after each round, increase the grain of the sandpaper by 100 to 150.
Once you have a smooth surface, you can apply the primer. The role of the primer is to help the paint adhere to the model. You should perform this step with each print no matter what painting method you use. The only exception is nylon, but we’ll get to that later.
The easiest way to apply a primer is by using a spray primer because it’s beginner-friendly. So, clean and sand the 3D print and then apply the primer in a couple of very thin coats. For a higher quality finish, you should sand the model lightly after each coat, but the most important ones are the first and the last. Just make sure to read the instructions on the primer to know how long each layer needs to dry.
Now, we can start painting the model. We have a few painting methods at our disposal, so let’s start with the most obvious one.
Painting with a brush
The paintbrush method works best with ABS, PLA, and PETG. It’s ideal when you want the model to have a unique, handmade design. You’ll have to experiment a bit until you find the best brush, but you can start out with just one or two flat ones. Here’s how to choose your brush and how to use it:
- The paintbrush should be somewhat stiff due to the paint’s viscosity.
- The shape of the handle and the type of bristle is up to you. See what’s the most comfortable.
- While painting, take regular breaks to check the brush for dry paint flakes. You should clean it whenever the paint dries otherwise the flakes will stick to your model and we don’t want that.
- Once you’re done painting, clean the brush and store it correctly with the bristles upwards.
With the right brush, the painting will be an effortless task, so feel free to try different ones to see what works for you. If you feel like the brush is dragging itself across the model’s surface, then it’s time to try a new one.
But you can’t use a paintbrush without the paint. Using the brushing method, you should only use acrylic paints for the best results. Before applying any, you should lightly sand the model (after applying the last primer layer). This increases the adhesion. Paint evenly in thin coats and let it dry for the amount of time specified by the manufacturer. Finally, don’t use so much paint that it starts forming droplets. Less is more.
This painting method will work best on ABS, PLA, and PETG. Using a spray can is sometimes easier than using a brush because you can apply more even coats. When you choose the spray can make sure to check the nozzle. Some cans come with special nozzles that have various characteristics and applications. To use them, all you need to do is shake them spray thin coats from the distance recommended on the can. Just make sure to keep the nozzle clean and don’t spray upside down or horizontally or the paint won’t get through.
As for the spray paint, there are several options and most of them are good. The only important thing to watch out for is the color because some brands use RGB while others CMYK or RAL so the colors will differ.
The dye method works only with nylon. Using regular paint on nylon is challenging, but the dye is much easier to apply because nylon is hygroscopic. Just don’t try it on other types of filaments, like PLA, because the dye won’t stick. Furthermore, for the best results, you should work with transparent and white nylon only or the dye won’t be noticeable.
To apply the dye, start by reading the label. Each formula comes with different instructions. Then start by cleaning and sanding the model. But make sure you don’t scratch or damage the surface of the print because the dye won’t cover it up. Whatever you see on the undyed model will be visible after dying it as well, even if you use dark colors.
Next, mix the dye with water and bring it to the required temperature as specified on the label. Now, the easiest way to apply the dye is to submerge your model in the dye. To keep it down you can attach a weight. After leaving it for the specified amount of time, take it out and wash it with cold water.
Getting the paint to stick
The reason why paint sticks to a surface is because of the surface energy difference between a liquid and a solid material. Whatever has the highest surface tension will automatically win. This factor is measured in dynes, and ideally, the paint should be ten units under the value of the solid material. This difference between the two tells us that the liquid is capable of covering the solid.
There’s a cool trick that can tell us how well a liquid paint will wetten the surface of a solid material. All you need to do is drop a bit of paint on the model’s surface. If the paint turns into a spherical shape, there’s too much surface tension for it to attach itself to the object. If it spreads out instead, then we’re good to go.
That being said, not all materials are equal when it comes to paint application. For example, painting ABS and PLA is quite simple, but PETG is a bit more challenging. There’s no difference in the painting process, however, getting the paint to stick properly to PETG can be difficult, especially when we want the finish to last for years. The only thing we can do is paint the model by following the instructions and hope for the best. After all, we can always remove the finish in the future and start over.
As for nylon models, paint has a hard time sticking to them. Sure, it’s possible, however, heat is necessary to increase the level of surface tension. Professionals use a fire source or plasma, and that’s not something you want to play with at home when you have other options like using dye.
To increase the chances of paint sticking properly, you should plan the entire process even before 3D printing. There are a few considerations and adjustments you can make before getting started:
- If you want to lower the amount of production time or if you’re working on a simple model, consider reducing the print resolution. This way you can invest more time and effort into the post-processing phase. However, this might be a bad idea with highly detailed models.
- Pay attention to the geometry of your model. Remember that sanding and cleaning are required in between the coats of primer and paint. If you aren’t careful, you might end up with blind spots that you can’t properly sand because the geometry doesn’t allow you to.
- Make sure the structure can handle the painting process. If your model has very fine and intricate details, it should be sturdy enough to withstand the sanding and the application of primer/paint.
- Are the details too small? Several layers of primer and paint can cover them up. Keep that in mind or you’ll end up with a less detailed final product.
- Sanding reduces the structural integrity of your model. Is it resilient enough? Check the smaller pieces and the fine details.
- Are measurements highly important? When you sand the model you’ll reduce its dimensions to a certain degree. The opposite happens when you add a few layers of primer and paint. Take that into account and print a slightly larger or smaller model to compensate.
After printing your model with these considerations in mind, you can start painting it. But you can do more to make sure the paint sticks properly. Here are a few tips on increasing adhesion:
- Don’t touch the 3D print with your bare hands. Your skin is covered in natural oils and they can repel the paint or form a protective coating that doesn’t allow it to pass. Always wear latex or rubber gloves when handling an unpainted model.
- Clean the model from any contaminants before sanding it. If you sand a dirty model, you might end up pressing the contaminants into the material. So clean your model using some isopropyl alcohol (while wearing gloves) and then sand it.
- While sanding, use a vacuum cleaner to suck out the dust immediately. Otherwise, it can get inside the finely detailed areas and clog them.
- Before painting and priming, you should test all products. Create small 3D printed samples and use the chemicals on them to see the result.
Like with anything else in 3D printing, learning how to paint and finish your model takes time and practice. So try painting different materials and see what’s easier to work with. Try various brands of paints and practice your brushing skills, or just use a spray can. You need to find what works best for you and your production setup and process.
As mentioned earlier, post-production involves more than just painting your model. Painting is just one of the steps. Here’s a quick breakdown of the typical post-production process to help you understand how to create an awesome model:
- Plan your model digitally with post-production in mind.
- Focus on high-quality settings instead of high-speed settings.
- Print the model
- Use filler material if necessary and then sand the model.
- Use filler primer (optional) and then sand the model again.
- Use a regular primer and sand the model after the first and last coats.
- Paint the model using any of the methods described above. Using an airbrush or spray can is the easiest for a beginner.
- Paint multiple colors by using painter’s tape to cover certain areas.
- Apply multiple coats of light to dark colors if you want layers and shades.
- Clearcoat the model.
Run one of your models through this entire process and compare it to a model that didn’t benefit from any kind of post-processing. You’ll notice that even with the skills of a novice the finished model looks much better.
Painting is just the most noticeable part of post-processing. It allows you to unleash your creativity and create amazing looking prints. So, experiment with different materials and try any methods you come across. Just don’t forget to follow the instructions of any product you use and take all safety precautions. Wear gloves, protect your eyes, and don’t paint in a closed space. Those fumes are terrible for you and sometimes even flammable. Paint in a ventilated room or even outside if you have to.
A painted model will be cherished for years to come compared to an unfinished model. All it takes is a few practice runs and you’ll gain enough skill to create display case-worthy 3D prints.
Here's a kit that I personally use and recommend for painting