How to Smooth a 3D Print? 5 Methods Explained

Here are the 5 most common ways to smooth your 3D print:

• Sanding is the foundation and works on any material. It’s cheap, but it takes time and elbow grease.
• Filler primer or spray putty fills in the layer lines and is ideal for preparing a print for painting.
• Epoxy coating (like XTC-3D) creates a smooth, glossy, and sturdy surface in one go, without endless sanding.
• Polishing brings a sanded print to a high shine, but only works after thorough sanding.
• Acetone vapor (vapor smoothing) makes an ABS print mirror-smooth without sanding, but does not work on PLA or PETG.

One important thing to note upfront: you can never completely get rid of the typical ribbed texture of an FDM print (a print built layer by layer) on its own. But with the right method, you can get surprisingly close to a factory finish.

First things first: why is a 3D print rough?

An FDM printer builds your object by laying down molten plastic layer by layer. Each of those layers is a fraction of a millimeter thick, but together they create a visible stair-step effect on sloped and rounded surfaces. We call these layer lines.

The thinner you print the layers (the layer height), the less visible they are, but they never disappear completely. Smoothing is all about removing or filling in those layer lines.

Good to know before you start: sanding removes material. For parts that need to fit precisely, have threads, or feature snap-fit connections, this can ruin the dimensions. Work carefully there or avoid it altogether. Want to know how layer height affects smoothness? Read all about layer height in 3D printing.

Method 1: Sanding (the foundation for almost everything)

Sanding is the most common way to smooth a print and the foundation for almost every other method. You wear down the peaks of the layer lines until the surface feels even. It works on every material and doesn't cost much, but it does require time and patience.

What you need:

• Waterproof sandpaper (also known as wet/dry sandpaper) in increasing grits: 120, 220, 400, 600, 1000, and optionally 2000. The lower the number, the coarser the grit. You can find this at any hardware store or in the sandpaper category at 123-3D.
• A bowl of water with a few drops of dish soap.
• A sanding block or a flat piece of wood for flat surfaces.
• Optionally, sanding sponges or sanding sticks for details.

How to do it:

1. First, remove all support remnants and any burrs.
2. Start with the coarsest grit you need. For significant imperfections, start around 120; for light layer lines, start around 220.
3. Sand wet: regularly dip the sandpaper and the print into the soapy water. This dissipates heat, prevents the paper from clogging, and keeps dust down.
4. Work in calm, steady motions. Rinse the print occasionally so you can see your progress.
5. Step up to a finer grit each time: 120 → 220 → 400 → 600. Each step removes the scratches from the previous one. 400 to 600 is enough for painting; for a smooth or glossy look, keep going to 1000 and 2000.

Sanding is inexpensive, works on any material, and gives you great control over the final result. The downside is that it’s labor-intensive and time-consuming. For deep layer lines, sanding alone won't cut it—you'll need a filler method.

A few things that make a difference: sand wet, especially with the finer grits, as it makes a huge difference in the final result. Use a sanding block for flat surfaces, otherwise, you’ll accidentally sand waves into the surface.

Don't press too hard; let the grit do the work, because too much pressure creates deep scratches that you'll just have to sand out later. And don't use power sanding tools on PLA: the friction heat will cause the material to melt and smear. PLA starts to soften around 55–60°C.

Method 2: Filler primer or spray putty (filling layer lines)

While sanding removes material, this method fills in the layer lines. Filler primer (a thicker primer from a spray can that fills small imperfections) and spray putty are ideal if you're planning to paint the print anyway. They make the surface uniform and ensure the paint adheres well later on.

What you need:

• A spray can of filler primer or spray putty. Available at hardware stores and online at 123-3D.
• Sandpaper in 220 to 400 grit for in-between steps.
• A well-ventilated area or an outdoor spot.
• A face mask and, optionally, gloves.

How to do it:

1. Lightly sand the print first (around 220 grit) so the primer adheres well.
2. Make sure the print is dust-free and completely dry.
3. Spray a thin layer of filler primer from about 20–30 cm away.
4. Let it dry. You will notice that the imperfections become more visible, which is exactly the point.
5. Lightly sand the layer back with 320 to 400 grit. The primer will stay in the layer lines, while you sand the high spots smooth.
6. Repeat steps 3 through 5 until the surface is completely smooth. Usually, two to three coats are enough.

The big advantage is that this method fills in layer lines that you can't remove by sanding alone, making it the perfect preparation for painting. On the downside, you are adding a thin layer, which makes it less suitable for parts with tight tolerances. And you still have some sanding to do in between.

Always work in thin layers, because a thick layer will drip and dry unevenly. Use primer and any paint from the same brand to ensure they adhere to each other. Never spray indoors without ventilation, as the fumes are unhealthy. And don't skip the sanding between coats, otherwise the layer structure will remain visible.

Method 3: Epoxy coating like XTC-3D (smooth in one go)

Do you want a smooth and glossy surface without endless sanding? Then an epoxy coating is the solution. The best-known product for this is XTC-3D from Smooth-On: a two-component epoxy that you brush over the print.

The liquid resin flows into the layer lines and cures into a smooth, sturdy layer. It makes the print a bit stronger right away and provides a good base for painting.

What you need:

• A two-component epoxy coating like XTC-3D (can be ordered online at 123-3D).
• A brush or foam sponge to apply it.
• Disposable gloves and a surface you don't mind getting dirty.
• Fine-grit sandpaper (600 to 1000 grit) for the finishing touches.

How to do it:

1. Carefully mix the two components (resin and hardener) according to the ratio on the packaging. Stir gently to avoid creating air bubbles.
2. Note: most epoxy has a working time of only 10–15 minutes. Don't mix too much at once and work quickly.
3. Apply a thin layer with your brush or sponge. Spread it evenly and make sure it doesn't pool in crevices or details.
4. Let it cure completely according to the manufacturer's instructions (usually a few hours).
5. One coat is usually enough to smooth things out. For a perfect result, lightly sand afterwards with 1000 grit and apply a second coat if needed.

The big plus is that you get a smooth, glossy surface in one go with much less sanding, while also making the print stronger and partially water-resistant.

The downside is that you're working with chemicals, so ventilation and gloves are a must. The short working time requires preparation, and fine details can get slightly blurred by the coating.

Mix accurately, because the wrong ratio means the epoxy won't cure properly and will stay sticky. Have everything ready before you start, because the clock is ticking as soon as you mix. Don't use this method on fine, detailed miniatures, as the layer can soften sharp details. And never work without gloves: uncured epoxy should not touch your skin.

Method 4: Polishing (for a high-gloss finish)

Polishing is the finishing touch if you want a truly shiny, almost mirror-like surface. Note: polishing only works after thorough sanding. It doesn't remove layer lines; it brings an already smooth surface to a high gloss.

What you need:

• A thoroughly sanded print (up to at least 2000 grit).
• Plastic polishing compound or polishing paste.
• A soft (microfiber) cloth or a polishing pad.
• Optionally, a polishing cloth for the final shine.

How to do it:

1. Make sure the print has been wet-sanded to a very fine grit (2000 or higher) and is completely clean and dust-free.
2. Apply a small amount of polishing compound to your cloth.
3. Rub the surface in circular motions, using light pressure.
4. Keep polishing until the shine appears. Add more polishing compound if necessary.
5. Finish with a clean, dry cloth for the final gloss.

Polishing creates a high-quality, glossy finish that you can't achieve with sanding alone. It does require a lot of prep work, as you must first sand the print completely to a high grit. And naturally, it’s not the right choice if you want to keep the print matte.

Sand thoroughly first, because polishing a print with visible layer lines won't work: the lines will just become shiny too. Use a polishing compound suitable for plastic, and avoid aggressive agents with solvents that could damage the material.

Finally, don't polish with a high-speed machine if you don't have experience with it, as the heat can melt the surface.

Method 5: Acetone vapor (for ABS & ASA only)

Finally, a method that provides a mirror-smooth result without sanding: vapor smoothing with acetone vapor. In this process, you hang the print in a sealed container with some acetone. The vapor dissolves the surface very lightly and evenly, causing the layer lines to flow together into a glossy finish.

Note: this only works on ABS (and the related ASA). Acetone does not work on PLA and PETG, the two most popular materials. For those materials, you should stick to the other methods.

What you need:

• An ABS or ASA print.
• Acetone (available at hardware stores or pharmacies).
• An airtight container that is acetone-resistant, plus some paper towels or a cloth.
• A well-ventilated area, nitrile gloves, and preferably a mask.

How to do it:

1. Line the inside of the container with paper towels and lightly dampen them with acetone. The print itself should not touch the acetone.
2. Place the print on a small stand inside the container so that it is only exposed to the vapor.
3. Close the container and let the print sit in the vapor for 10 to 30 minutes. Keep a close eye on it.
4. Remove the print as soon as the surface becomes glossy. Let it air out and dry completely (for a day) before touching it.

The beauty of this method is that you get a mirror-smooth finish without any sanding or elbow grease, which is perfect for decorative ABS prints. However, the downsides are significant: it only works on ABS and ASA, acetone is flammable, and the fumes are harmful. Plus, fine details will blur because the material literally dissolves slightly.

Work in a well-ventilated area, far away from open flames or sparks. Monitor the process continuously, because if you leave it in the vapor for too long, your print will warp. Don't try this on PLA or PETG, as it won't work and you'll just be wasting acetone. And don't touch the print while the surface is still soft, or you'll leave fingerprints in it.

Which method should you choose?

Here’s a quick summary so you know exactly where to start.

• Want to keep it simple and cheap? Start with sanding. For most prints, that’s enough.
• Are you going to paint the print? Sanding followed by filler primer is the golden combination for a smooth base.
• Want it smooth and glossy without endless sanding? Choose an epoxy coating like XTC-3D.
• Looking for a high-gloss finish? Sand it completely and then polish it.
• Do you have an ABS or ASA print and want it mirror-smooth without sanding? Then acetone vapor is the fastest route.

Want to have your print made so you only have to do the finishing work yourself? Request a free printability check or calculate your price directly in our 3D print price calculator.

Frequently asked questions about smoothing 3D prints

Can you get a 3D print completely smooth?

Almost, but it takes some effort. By combining sanding with a filler method (filler primer or epoxy), you can get very close to a factory finish. The layer lines will disappear, though achieving a perfect mirror finish without coating or polishing remains difficult.

Should I sand wet or dry?

Wet sanding is almost always preferred for plastic. The water dissipates heat (so the material doesn't melt), keeps dust down, and prevents your sandpaper from clogging. Especially with finer grits, wet sanding makes a big difference.

Can I smooth PLA with acetone?

No. Acetone doesn't work on PLA. The acetone vapor method only works on ABS and ASA. For PLA, you should use sanding, filler primer, an epoxy coating, or polishing.

What grit sandpaper do I need?

That depends on your starting point and your goal. For rough imperfections, start around 120 to 220 grit. For painting, sand up to 400 or 600. For a smooth or glossy finish, work your way up to 1000 or 2000. Always progress from coarse to fine.

Does smoothing make my print stronger?

Sanding and polishing do not. An epoxy coating like XTC-3D does: it adds a sturdy layer that makes the print slightly stronger and partially water-resistant. Do you need a print that can withstand water? Read how to make a print waterproof and which filament to choose.

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