Do You Need to Prime 3D Prints Before Painting

When preparing to paint a 3D printed part, one important question often comes up — is priming necessary? In most cases, applying a primer before painting makes a noticeable difference in how the part looks and how well the paint holds over time.

This post explains why priming is often a smart choice, when it might be skipped, and how to approach the priming process, including specific tips for SLS printed parts.

Why Priming 3D Prints is a Good Practice

Priming improves both the appearance and durability of painted 3D printed parts. It smooths uneven surfaces, helps paint stick properly, and creates a neutral base color that allows paint to go on evenly.

Parts made using FDM 3D printing often show visible layer lines and small gaps. Primer helps to fill these and prepare the surface for a smoother paint application. Without primer, paint can settle unevenly into the layer lines or fail to bond well to the plastic, which may lead to peeling or cracking later on.

SLS prints, typically made from nylon, bring a different challenge. Their surfaces are naturally porous and can feel rough. This porosity makes paint absorb unevenly and can cause a patchy finish if primer is skipped. Applying primer to SLS parts helps seal the surface, making it much easier to achieve a smooth and consistent paint layer. For SLS 3D print parts, primer is an important part of post-processing.

When Priming Might Not Be Necessary

Priming is not always required, though these cases are less common. If a resin-printed part already has a smooth surface and will only be painted for quick visual purposes, priming might be optional. Some spray paints include built-in primers and can sometimes be used directly on the part. However, these combined products may not offer the same level of smoothness or long-term durability as a separate primer.

Basic Steps for Priming 3D Prints

Start by sanding the part if needed to reduce surface texture. Sandpaper between 200 and 400 grit usually works well for this. Once sanding is done, clean the part to remove dust and residue. A lint-free cloth or isopropyl alcohol helps prepare the surface.

When applying primer, choose one that bonds well to plastic. Spray a light first coat and let it dry before applying additional layers. Multiple thin coats work better than a single heavy coat, as this avoids drips and keeps surface details clear. If a very smooth finish is required, light sanding between coats can improve the result. After the final primer layer is dry, the part is ready for painting.

Choosing the Right Primer

Primers designed for automotive or plastic surfaces are often the best choice. Automotive filler primers are useful for covering visible layer lines on FDM prints. For SLS nylon parts, a primer that bonds specifically to plastic helps seal the surface and prepares it for paint.

If you are working on improving your post-processing quality, you may also be interested in learning how to smooth 3D prints.

Why It Makes Sense to Prime 3D Prints

Priming is a step that improves both the appearance and durability of painted 3D prints. Whether working with FDM or SLS parts, when you prime 3D prints, it helps create a better foundation for paint and leads to cleaner, longer-lasting results. If you need advice on choosing the right 3D printing technology and post-processing tips, feel free to contact us for guidance.