How to Smooth PLA Prints: 7 Methods That Work

Reading time: 8 min

Anyone who does 3D printing knows the problem: prints in PLA filament come off the printer with visible layer lines, small bumps and sometimes a rough surface. The print can be spot on for size and detail, yet the finish still leaves a lot to be desired. Fortunately, there are plenty of proven ways to smooth PLA, and they can make your 3D printed models look dramatically better.

In this article we go through the most effective post-processing techniques for PLA prints, from mechanical methods to chemical processes, so you can get a smooth, professional finish.

Why do PLA prints need smoothing?

A 3D printer builds a model layer by layer, which by definition leaves visible lines between the layers. Even at a fine resolution (for example a 0.1 mm layer height), these lines stay noticeable, especially when light hits the surface at certain angles.

The main causes of an uneven surface are:

• Visible layer lines: the natural result of FDM/FFF printing
• Stringing and blobs: excess material from oozing and poorly tuned retraction
• Imperfect calibration: leading to uneven extrusion
• Support marks: scars left where support structures touched the model
• Warping: slight deformation along the edges

‘Post-processing a 3D printed model matters as much as the printing itself. It turns a good print into an excellent finished piece.’ – a rule of thumb in professional 3D printing

Mechanical methods for smoothing PLA

Sanding: the go-to method

Sanding is the most accessible and controllable way to smooth PLA prints. It takes patience, but the results are predictable and effective.

How to sand properly:

1. Coarse (80–120 grit): removes visible bumps and support marks
2. Medium (150–240 grit): levels the surface
3. Fine (320–600 grit): leaves a smooth surface
4. Polishing (800–2000 grit): for a mirror finish (optional)

Sanding tips:

• Work in a well-ventilated room
• Wet sand for better results and less dust
• Sand in small circles rather than in one direction
• Apply even, moderate pressure
• Clean built-up material off the sandpaper regularly

Rotary tools

For complex shapes and hard-to-reach spots, a rotary tool such as a Dremel is invaluable for post-processing 3D prints:

• Sanding bits: for rough work
• Polishing bits: for a final shine
• Brushes: for textured surfaces

Caution: keep the speed low (5,000–10,000 RPM) so friction doesn't melt the PLA.

Trimming with a sharp blade

To remove strings, blobs and leftover bits of support, use:

• A hobby knife (X-Acto)
• A scalpel
• Dedicated 3D print finishing tools

Always cut away from yourself, and keep the blade sharp for clean cuts.

Chemical methods for smoothing PLA

Solvent smoothing (limited use)

Unlike ABS, which smooths easily with acetone vapour, PLA resists most solvents. Even so, a few approaches do work:

Tetrahydrofuran (THF):

• Effective on PLA, but extremely hazardous
• Toxic and a suspected carcinogen
• NOT recommended for home use
• Requires professional equipment and protection

Ethyl acetate:

• A safer alternative to THF
• Moderately effective on PLA
• Still needs good ventilation
• Can be used for partial smoothing

Important: chemical smoothing of PLA carries significant health risks and isn't recommended for beginners, or for home use without the right equipment.

Heat smoothing

Controlled heat can even out surface imperfections on PLA without any chemicals.

The hot air method:

1. Use a heat gun on its lowest temperature setting
2. Hold it 15–20 cm from the object
3. Move it quickly and evenly
4. Stop as soon as the surface turns glossy

Risks:

• The model deforms easily
• Fine detail can be lost
• It takes practice and experience

Epoxy coating

A thin coat of epoxy resin doesn't just smooth a PLA print, it also strengthens it:

• Mix a two-part epoxy resin according to the instructions
• Brush on a thin, even coat
• Leave it to cure as long as the manufacturer recommends
• If needed, sand and polish once it has hardened

Coatings and fillers

XTC-3D and similar coatings

XTC-3D is a two-part coating made specifically for smoothing 3D prints.

Advantages:

• Self-levelling
• Leaves a smooth, hard surface
• Easy to apply
• Works on all common FDM materials

How to apply it:

1. Clean the surface thoroughly
2. Mix the two parts at the manufacturer's ratio (2:1 by volume for XTC-3D)
3. Brush it on or pour it over the model
4. Let the excess run off for 2–3 minutes
5. Leave it to cure for 4 hours

Filler primer and acrylic fillers

Automotive fillers and dedicated 3D printing primers are an excellent way to fill in layer lines.

How to work with them:

1. Spray on filler primer in thin coats
2. Let it dry
3. Sand lightly with fine sandpaper (400–600 grit)
4. Repeat 2–3 times until you get the result you want
5. Finish with a top coat of paint

This method works especially well before you paint a model.

Bondo and car body filler

For bigger imperfections and filling gaps:

• Apply it with a spreader
• Let it harden
• Sand it to the shape you want
• Suits functional, structural models rather than detailed figurines

PLA smoothing methods compared

Get a smoother finish straight off the printer

The best route to a smooth surface is to optimise the 3D printing itself.

Slicer settings:

• Layer height: 0.1–0.12 mm for fine detail
• Temperature: the optimum for your particular PLA (usually 200–215 °C)
• Speed: slower printing (40–50 mm/s) for better quality
• Retraction: tuned correctly, it prevents stringing
• Cooling: enough part cooling for crisp edges

Settings for a smoother outer wall:

• Enable ‘Outer wall wipe distance’
• Use ‘Z-hop’ on retraction
• Fine-tune the ‘Coasting’ settings
• Reduce the ‘Line width’ for outer walls

Model orientation:

Orienting the model well on the print bed can dramatically reduce the post-processing it needs:

• Place the model so its visible surfaces are perpendicular to the print bed
• Keep supports off visible areas as far as you can
• Think about the direction of the layers in relation to what the part has to do

Combining techniques for a professional finish

For a truly professional finish, combine several methods.

Recommended sequence:

1. Clean-up: remove supports and rough bumps
2. Coarse sanding (120–240 grit): level the surface
3. Filling: apply primer or XTC-3D
4. Fine sanding (400–800 grit): refine the finish
5. Polishing: for a mirror-like surface (optional)
6. Painting: the final coat (if you want one)

Tips by type of print

Functional parts

For parts that will be used mechanically:

• Focus on the surfaces that matter
• Use epoxy resin to strengthen them
• Don't sacrifice dimensional accuracy for looks

Display models and figurines

For display pieces (such as Warhammer miniatures or lithophanes):

• Invest time in sanding through several grits
• Use XTC-3D or a similar product
• Finish with a good-quality paint job
• Polish to a high level of smoothness

Prototypes

For quick prototypes:

• Use spray filler primer for a fast result
• Focus on the overall look, not perfection
• Pick out the key details with a marker

Post-processing safety

When you work on 3D printed models and with chemicals, take these precautions.

Personal protection:

• Wear a suitable mask (FFP2/FFP3 when sanding)
• Use safety glasses
• Wear gloves when handling chemicals
• Wear work clothes

Workspace:

• Make sure the ventilation is excellent
• Work outdoors or in a workshop with dust extraction
• Don't eat in the work area
• Store chemicals properly

Waste disposal:

• PLA dust and particles: general waste
• Chemicals: according to local regulations
• Used sandpaper: general waste

Common mistakes and how to avoid them

Sanding too aggressively

Problem: lost detail and a distorted shape

Solution: work gradually, check often and switch to finer sandpaper

Uneven coating

Problem: drips and bumps in XTC-3D or resin

Solution: apply thin coats, rotate the object and use a brush

Melting the material while polishing

Problem: heat deformation from a Dremel

Solution: lower speed, less pressure and frequent breaks

Poor preparation before painting

Problem: the paint peels and the surface is uneven

Solution: prime properly and sand between coats

Conclusion

Smoothing PLA prints is a skill that grows with practice. There's no single ‘best’ method. Each approach has its strengths, depending on the project, the time you have and the result you want.

If you're a beginner, we recommend starting with sanding and spray filler primer. Both are safe, affordable and give predictable results. As you gain experience, you can try more advanced techniques such as XTC-3D or a combination of methods.

Remember that the quality of the final piece depends not only on post-processing but also on well-tuned printer settings. Time spent on calibration and on experimenting with your settings pays off in a better result straight off the printer.

Need something 3D printed in Bulgaria?

If you'd rather not deal with printing yourself, or you need a specific project printed well, the 3dpechat.bg team can help. We're a 3D printing service in Sofia and print with FDM technology. PLA is our main material and the one we keep in stock; other materials, such as PETG or TPU, are possible on request, and we buy them specially for your order.

You can start from a ready 3D model, a sketch, a photo or just an idea. Send your files (STL, 3MF, OBJ or STEP) by email. The first quote and the consultation are free, and we usually reply within 24 hours. Get in touch through the enquiry form or email, or work out a rough price first with our price calculator.

Get in touch today and let's turn your 3D idea into a finished print.