The Ultimate 2025 Guide

Painting a 3D print changes it from a basic plastic item into a finished product, a detailed miniature, or a realistic prototype. However, the process involves more than just adding a layer of color. A great paint job starts with careful preparation. This guide gives you a complete, expert-led process for turning your raw FDM and resin prints into professionally finished pieces. We will cover every important stage, from initial cleanup and surface smoothing to advanced detailing and final protective sealing.

Why Preparation Is Key

The biggest mistake when learning how to paint 3d prints is rushing the preparation stage. Raw prints, especially from FDM printers, have clear layer lines, and both FDM and resin prints can have flaws from support structures. Paint is not a filler; it's a thin film that follows the surface shape. Without proper preparation, every layer line and flaw will show up more, not less. A smooth, well-prepared surface is the only way to get a perfect finish. The time you spend on preparation pays off in the final result.

Post-Print Cleanup

Your work begins the moment the print is finished. The first step is to clean the raw part and remove any temporary structures.

Removing Supports

Support structures are needed for many complex 3D prints. Removing them cleanly is your first post-processing challenge. For FDM prints, use different tools. Pliers can break off large sections, while flush cutters let you cut away supports close to the model's surface. A sharp hobby knife is essential for carefully cutting away stubborn contact points. For resin prints, it is often best to remove supports after an initial wash but before the final cure. The partially cured material is less brittle, reducing the risk of creating dents or "craters" on the model's surface. Always work carefully to avoid damaging the print itself.

Initial Sanding

After support removal, you will have small bumps or rough patches. A quick initial sanding pass is needed to smooth these down. Use coarse sandpaper, something in the 120 to 220 grit range. The goal here is not to get a perfect surface, but to remove the most obvious high spots and flaws. This creates a more even starting point for the intensive smoothing process that follows.

Material-Specific Concerns

The two most common 3D printing technologies, FDM and SLA, produce parts with very different surface characteristics. Your approach to smoothing must be adjusted accordingly.

FDM Prints (PLA, ABS, PETG)

Fused Deposition Modeling prints are built layer by layer, resulting in the characteristic layer lines that are the main obstacle to a smooth finish. Your entire smoothing process for FDM will focus on hiding these lines. Sanding is the most direct method, but for prints with deep layer lines, it can be a long and labor-intensive process. This is where fillers and special primers become very helpful.

Resin Prints (SLA/DLP)

Stereolithography and other resin-based printing methods produce parts with a much smoother initial surface finish, often with no visible layer lines. The main challenge here is dealing with the small bumps left by support contact points. It is important to ensure your resin print is properly washed and fully cured before you begin any aggressive sanding. Sanding uncured or partially cured resin is a safety hazard and produces a poor finish. Always wear gloves when handling uncured resin and a respirator mask when sanding to avoid breathing in fine particles.

The Art of Sanding

Sanding is a required step for achieving a high-quality painted finish. It is a process of improvement, where you systematically remove scratches with progressively finer scratches until they are invisible to the naked eye.

Wet vs. Dry Sanding

While you can sand prints dry, we strongly recommend wet sanding. By dipping your sandpaper in water, you gain several advantages. The water acts as a lubricant, leading to smoother action and a finer finish. It also captures the plastic dust, preventing it from becoming airborne, which is better for your health. Finally, the water helps prevent the sandpaper from "clogging" with plastic, extending its life and making your work more efficient.

Progressive Grit Sanding

The key to successful sanding is progression. Do not jump from a very coarse grit to a very fine one. Start with a lower grit, around 220, to remove the primary imperfections. Once the surface is uniform, move to a higher grit, like 400, to remove the scratches left by the 220 grit paper. Continue this process, moving through 600, 1000, and even higher grits if you want a glass-like surface. Each step should focus on removing the marks of the previous one. This methodical approach is the only way to achieve a truly smooth canvas for your paint.

Filling Imperfections

Sanding alone may not be enough to hide deep layer lines or stubborn gaps. This is where fillers come in. A filler is a paste-like material used to fill dents, seams, and other imperfections, which is then sanded smooth.

Choosing a Filler

There are several categories of fillers suitable for 3D prints. Two-part epoxy putties are excellent for filling large gaps and can be shaped before they cure. Automotive spot putties are thinner and are perfect for glazing over a surface to fill minor scratches and pinholes. Some makers also find success with wood filler for FDM prints, as it is easy to apply and sand. For resin prints, a clever technique is to use a drop of the same liquid resin to fill a support bump, then cure it instantly with a UV flashlight before sanding.

Application Technique

The rule for fillers is to apply them in thin, targeted layers. Use a small spatula or hobby tool to press the filler into the gaps or scrape a thin layer over a textured area. It is better to build up two or three thin layers than to apply one thick, messy coat. Allow the filler to cure completely according to its instructions. Once cured, sand it flush with the surrounding surface, using the same progressive grit method as before. The goal is a seamless transition between the filler and the plastic.

The Spray-On Solution

For FDM prints with persistent layer lines, one of the most effective techniques when learning how to paint 3d prints is using a high-build or "filler" primer.

Using Filler Primer

This type of primer is a thick, sandable paint that does double duty. It primes the surface while also filling in microscopic scratches and small layer lines. The process is a cycle: apply a light coat of filler primer, let it dry completely, and then sand it smooth with a medium-grit sandpaper (e.g., 400 grit). You will see the primer come off the high spots while remaining in the low spots (the layer lines). Repeat this process two or three times. Each cycle builds up the low spots, bringing them level with the high spots, until you have a perfectly uniform, smooth surface.

Why You Must Prime

After all the sanding and filling, do not skip the final priming step. A dedicated primer is different from a filler primer; its job is not to fill, but to prepare the surface for paint. This step is critical for three reasons. First, it provides a consistent, adhesive layer that your color coats can grip onto, preventing chipping and peeling later. Second, it creates a neutral base color, ensuring that your reds look red and your blues look blue, without being influenced by the plastic color underneath. Finally, a thin, even coat of primer is the ultimate inspection tool. It will instantly reveal any tiny scratches or flaws you may have missed during the sanding phase.

Choosing Your Primer

Primers are available in aerosol spray cans or as liquids for airbrush application. For most users, aerosol primers are a convenient and effective choice. Look for primers specifically made for use on plastics for the best adhesion. The color of the primer matters. A grey primer is a fantastic all-purpose choice that works well under most colors. Use a white primer if you plan on painting with bright colors like yellow or orange. A black primer provides an excellent base for dark colors and is especially useful for creating dramatic shadows and metallic effects.

Priming Technique

Proper priming technique is essential for a smooth coat. Work in a well-ventilated area, free of dust, and with moderate temperature and humidity. Shake the can thoroughly for at least a minute. Hold the can about 6-10 inches away from the model and apply the primer in short, sweeping passes. It is far better to apply two or three very thin coats than one thick, heavy coat, which can hide details and create drips. Allow each coat to dry fully before applying the next. After the final coat is dry, inspect your model under a bright light. If you find any flaws, now is the time to go back, do a little spot-sanding, and re-prime that area.

Bringing Your Model to Life

With a perfectly primed surface, you are ready for the most rewarding part of the process: painting. The choice of paint and application method will define the final look of your model.

Choosing Your Paint

The most common and beginner-friendly paints for 3D prints are acrylics. They are water-based, meaning they have low odor and can be cleaned up easily with water. They come in a vast range of colors and are suitable for both brush painting and airbrushing (with proper thinning). Enamel and lacquer paints are solvent-based alternatives. They are known for their extreme durability and smooth finish but require more ventilation and specialized thinners for cleanup. For most projects, acrylics offer the best balance of performance and ease of use.

Application Methods

There are three primary ways to apply paint to your model.

Brush Painting

Hand brushing is the most accessible method and offers the most artistic control. It is ideal for painting miniatures, adding fine details, and creating effects like weathering. The key to good brushwork is to thin your paints. A drop of water or acrylic thinner will break the surface tension and allow the paint to flow smoothly from the brush, eliminating brush strokes. Apply multiple thin, translucent coats rather than one thick, opaque one to build up rich, smooth color.

Spray Painting

Aerosol spray cans are not just for priming. They are excellent for applying base coats or painting large models with a single, uniform color. The technique is identical to priming: use short, even bursts while keeping the can moving. This method provides a very smooth finish with minimal effort, but it lacks the precision for detailed work.

Airbrushing

An airbrush is the ultimate tool for the serious painter. It atomizes paint into a fine, controllable spray, allowing for incredibly smooth base coats, seamless color gradients, and precise detail work. While airbrushing has a steeper learning curve and requires an initial investment in equipment (the airbrush and a compressor), it offers a level of quality and control that is unmatched by other methods.

Advanced Detailing

Once your base colors are down, you can add details that will make your model stand out.

Masking

To create crisp, clean lines between different colored sections, use masking. Painter's tape is the most common tool. Apply it firmly to the area you want to protect, pressing down the edges to prevent paint from bleeding underneath. For complex curves, specialty modeling tapes are more flexible. Liquid mask is another option, where you paint a rubbery fluid onto the model, let it dry, and then simply peel it away after painting.

Washes and Weathering

A wash is a very thin, dark paint that is applied liberally over a surface. Gravity and capillary action pull the dark pigment into the recesses, panel lines, and crevices of the model. When the excess is wiped away from the raised surfaces, the wash remains in the details, instantly creating a sense of depth and shadow. This is one of the fastest ways to add realism.

Dry Brushing

Dry brushing is the opposite of a wash; it is used to highlight raised details. To do this, dip a flat brush in paint, then wipe almost all of it off on a paper towel until the brush seems dry. Lightly drag the brush back and forth over the raised textures of your model. The tiny amount of remaining pigment will catch only on the highest points, creating a natural highlight effect that makes details pop.

The Final Protective Seal

After your paint job is complete and has fully dried, you must protect it with a clear coat or varnish. This final step is non-negotiable.

The Purpose of Sealing

A clear coat serves two functions. First and most importantly, it provides a durable, transparent shell that protects your hard work from scratches, chipping, moisture, and fading from UV light. Second, it unifies the finish of your model. Different paints can have different sheens, and a clear coat gives the entire piece a single, intentional finish.

Types of Clear Coats

Clear coats, typically applied from an aerosol can, come in three main finishes. A matte finish is completely non-reflective and is ideal for military models, realistic figures, and any object that shouldn't look shiny. A gloss finish is highly reflective and is perfect for creating a wet look, a polished car finish, or a candy-like sheen. A satin (or semi-gloss) finish is the middle ground, offering a slight sheen that looks natural on many surfaces. Choose the finish that best suits the subject of your model and apply it in the same way as primer: two to three light coats in a clean, dust-free environment.

Conclusion

Painting 3D prints is a skill that blends technical preparation with artistic application. As we've seen, the path to a stunning result follows a clear sequence: prepare the surface, smooth out all imperfections, prime for adhesion, apply your colors with care, and seal for protection. There are no shortcuts. Patience and a willingness to practice are your most valuable assets. Embrace the process, and you will find immense satisfaction in bringing your digital creations to life with color and detail.