The Complete Guide to Sandpaper Grit for 3D Prints (2025 Edition)

Your 3D printer has finished its work, but you're left with a part that shows obvious layer lines. Your goal is simple: turn this rough print into a smooth, professional-looking object. While there are many ways to improve prints after printing, sanding is still the most basic and easy-to-use method to get great results. Raw FDM prints and even some resin prints have flaws that hurt the final quality, and sanding directly fixes this problem. But success depends on one important question: "What grit sandpaper should I use?" This complete guide gives you the clear answer. We will explain the exact grit steps to follow, the detailed process, tips for different materials, and expert advice to help you get a perfect finish every time.

Why Sanding Is Important

Sanding does more than just make a print feel smooth; it completely changes how it looks. The main reason to sand is to remove layer lines. Sanding physically wears down the high and low spots of each printed layer, creating one smooth surface. This smooth surface is also important for preparing a print for a perfect finish. Paint, primer, and clear coats stick much better and look far superior on a properly prepared surface. Also, sanding is the perfect way to remove small print problems like tiny bumps, rough spots, and the uneven areas left by supports or stringing. For parts that need to work mechanically, sanding can be practical, letting you adjust sizes precisely so separate pieces fit together perfectly.

Sandpaper Basics

Understanding Grit Numbers

Understanding sandpaper is easy. The grit number shows how many rough particles there are per square inch. A lower number means fewer, bigger particles, which creates a rougher, more aggressive cut. A higher number means more, smaller particles, creating a smoother, less aggressive cut.

• Low Grit (like 60-220): Rough. Used for removing lots of material, like taking down big layer lines or shaping a part.
• Medium Grit (like 320-600): General smoothing. Used for removing the scratches left by low-grit sandpaper and starting the smoothing process.
• Fine/Ultra-Fine Grit (like 800-3000+): Finishing and polishing. Used for creating a surface ready for paint or polishing plastic to a high shine.

Wet vs. Dry Sanding

While you can dry sand 3D prints, it creates a lot of heat and dust. The rubbing can easily melt plastics like PLA, causing them to become gummy and clog the sandpaper.

Wet sanding is the best method for an amazing finish on most 3D prints. Dipping the sandpaper in water gives three key benefits: it acts as a cooler to prevent the plastic from melting, it traps dust particles in the water mixture to prevent them from floating in the air (which is much safer), and it continuously clears the sandpaper, preventing clogs. The result is a more efficient process and a noticeably smoother finish. A good rule is to use dry sanding for initial rough shaping and switch to wet sanding for all later smoothing and finishing steps.

The Best Grit Steps

The main rule of sanding is to start with a grit rough enough to remove the worst problems, then work your way up step by step. Each new grit's job is to remove the scratches from the previous grit. Never skip grits, as this will leave deep scratches that finer grits cannot remove, no matter how long you sand.

Stage 1: Heavy Shaping

• Grit Range: 120 – 220 grit
• Purpose: This is the hard-work stage. Use these rough grits to quickly remove support marks, elephant's foot, and the biggest layer lines. The goal is to level the surface, not make it smooth.
• Method: Use a sanding block on flat surfaces to keep them flat. Be careful that this stage removes material quickly. The surface will look rough and heavily scratched, which is what should happen.

Stage 2: General Smoothing

• Grit Range: 320 – 600 grit
• Purpose: This stage smooths the entire surface and removes the deep scratches left by the rough sandpaper. After this stage, your print will start to feel even to the touch, and the most obvious signs of layering will be gone.
• Method: This is the perfect stage to switch from dry to wet sanding. The water will help carry away plastic pieces and keep the surface cool.

Stage 3: Fine Finishing

• Grit Range: 800 – 1500 grit
• Purpose: Now we are creating a super-smooth, matte, or satin surface that is perfect for primer and paint. At this point, any remaining scratches will be almost invisible to the eye and will easily be filled by a coat of primer.
• Method: Wet sanding is essential here for the best results. The surface should feel silky smooth after this stage.

Stage 4: High-Gloss Polishing

• Grit Range: 2000 – 5000+ grit
• Purpose: This is an optional stage for getting a high-gloss, reflective finish without any paint or clear coat. It works best on hard, dark-colored plastics.
• Method: Use with plenty of water and very light pressure. For an even higher, mirror-like shine, this can be followed by applying a special plastic polishing compound with a microfiber cloth.

Quick-Reference Grit Chart

The Step-by-Step Process

Step 1: Prepare Your Work Area

Safety should always come first. Before you begin, put on a dust mask and safety glasses. Gather your tools: sheets or sponges of each sandpaper grit you plan to use, a sanding block, a bowl of water (adding a drop of dish soap can help reduce surface tension), and clean microfiber cloths. Before sanding, look at the print carefully. Use a deburring tool or a sharp hobby knife to carefully cut away any large bumps, stringing, or support leftovers. This makes the initial sanding stage much easier.

Step 2: Start Roughly

Begin with your roughest grit, for example, 220 grit. If you're working on a flat surface, wrap the sandpaper tightly around a sanding block to prevent rounding edges. Sand the part using gentle, circular motions to start breaking down the layer lines. You can also change directions (like left-to-right, then top-to-bottom) to ensure even material removal. The goal here is simply to level the surface. Don't worry that it looks very scratched; this is a necessary part of the process.

Step 3: Clean and Move Forward

This step is important. After sanding with your first grit, thoroughly wipe the print clean with a damp cloth. This removes the rough particles and plastic dust that would otherwise get caught in your next sandpaper grit and create new, deep scratches. Look at the surface. Are the major layer lines gone? If the surface is evenly scratched and leveled, you are ready to move to the next grit (like 400).

Step 4: Begin Wet Sanding

Now, add water. Dip your 400-grit sandpaper into your bowl of water and continue sanding. You will feel the difference right away. There is less resistance, no heat buildup, and the sandpaper moves more smoothly across the surface. Your goal in this step is to completely remove the scratch pattern left by the 220-grit paper. The surface will start to look and feel much smoother.

Step 5: Repeat and Improve

This is the main cycle of the sanding process. Continue the pattern: sand with a new grit, wipe the part completely clean, look at the surface, and move to the next higher grit (like 600 → 800 → 1200). With each step, the scratches you are creating become smaller and smaller until they are no longer visible, leaving a progressively smoother surface behind. Patience is key; make sure the scratches from the previous stage are gone before moving on.

Step 6: The Final Clean

Once you have reached your target smoothness, give the print a final, careful cleaning with a fresh microfiber cloth and water. Make sure it is completely free of all dust, slurry, and residue. Let it dry completely. Your part is now perfectly prepared for its final finish.

Material-Specific Tips

Sanding PLA

PLA has a low melting temperature, which is its biggest challenge during sanding. Friction creates heat quickly, causing the plastic to soften, melt, and "fuzz" rather than sand away cleanly. This also causes the sandpaper to gum up instantly. For PLA, wet sanding is not optional, it is required for almost the entire process. Use very light pressure and let the sharpness of the sandpaper do the work. Keep the surface and the paper wet at all times.

Sanding ABS

ABS is easier to work with than PLA. It has a higher melting point and is a harder material, so it tends to sand into a fine powder rather than melting. It can handle dry sanding better, especially for the initial shaping stages with rough grits. However, for the best possible finish, switching to wet sanding from the medium grits (320+) onward is still the better method. It produces a cleaner, smoother result with less effort.

Sanding PETG

PETG presents a unique challenge. It is tougher and has a slight flexibility that can cause it to "gouge" or "peel" if sanded too hard, rather than grinding away smoothly. The key is to use fresh, sharp sandpaper, as dull paper will make this problem worse. Wet sanding is essential to keep the material cool and lubricated. Use slower, more careful strokes and let the paper glide over the surface.

Sanding Resin Prints

Resin (SLA/MSLA) prints are hard and can be brittle, but they offer a great starting point since their layer lines are often microscopic. The biggest concern is safety; cured resin dust is more dangerous to breathe than plastic dust. For this reason, you must always wet sand resin prints to eliminate airborne particles. Always wear a proper respirator or mask as a primary precaution. Because the surface is already so smooth, you can often skip the roughest grits and start directly with 400 or even 600 grit.

Expert Tips and Common Mistakes

Tips for a Better Finish

• Use a Filler Primer: For prints with very deep layer lines, this technique is a huge time-saver. Do an initial sanding pass with 220-400 grit, then apply a thin, even coat of automotive filler primer. This type of primer is thick and designed to fill small problems. Let it cure fully, then sand the primer itself starting with 600+ grit. It's much easier and faster to sand primer than raw plastic.
• Use Sanding Sponges: For curved, organic surfaces and hard-to-reach internal corners, flexible sanding sponges or sticks are invaluable. They conform to the shape of the part, preventing the flat spots that a rigid sanding block can create.
• Let the Sandpaper Work: Do not use too much force. Pressing harder doesn't speed up the process; it just creates more heat, creates deeper scratches, and wears you out faster. Use light, consistent pressure.

Common Mistakes to Avoid

• Skipping Grits: This is the number one mistake. If you jump from 220 grit to 800 grit, the fine paper will not be able to remove the deep scratches left by the rough paper. The result is a part that feels smooth but has visible gouges under light.
• Sanding in One Direction: Constantly sanding back and forth in a single direction can create tiny, visible grooves in the plastic. Change your sanding pattern, using circular motions or changing directions to ensure an even finish.
• Forgetting to Clean Between Grits: If you don't wipe the part clean, rough particles from a previous stage will get trapped on your finer sandpaper, creating new deep scratches and undoing your hard work.
• Ignoring Safety: Microplastic and resin dust are harmful to your lungs. Always wear a dust mask or respirator, especially when dry sanding or working with resin.

Frequently Asked Questions

• Q1: Can I use an electric sander?

  • A: We suggest using them very carefully. A random orbital sander set to its lowest speed can work for large, flat parts and may speed up the initial rough sanding stage. However, it is very easy to apply too much pressure or stay in one spot for too long, which will instantly melt the plastic or remove too much material. Hand sanding offers far more control and is safer for detailed work.

• Q2: How do I know when to move to the next grit?

  • A: Look closely at the surface. You are ready to move on when the entire surface has an even pattern of fine scratches from your current grit, and you can no longer see any of the deeper, more distinct scratches from the previous, rougher grit. Wiping the surface dry will make this easier to see.

• Q3: What do I do after sanding?

  • A: After a final cleaning, your print is perfectly prepared for the next step. This usually involves applying a coat of primer to create an even surface for paint. After the primer, you can apply your choice of color and finish with a protective clear coat (matte, satin, or gloss) to seal your work.

Conclusion

The secret to a perfectly smooth 3D print is not a single tool or trick. It is a careful process built on patience. By following a step-by-step progression through the sandpaper grits and using the wet sanding technique, you can reliably remove layer lines and create a perfect surface. With this knowledge, you now have the skill to turn any raw 3D print into a professional-quality showpiece. Happy sanding.