PLA (Polylactic Acid) is one of the most popular 3D printing materials due to its ease of use, low cost, and biodegradability. However, PLA prints often have visible layer lines, which can affect the aesthetics and surface finish—especially for display models, prototypes, and artistic prints.
Unlike ABS, which smooths easily with acetone vapor, PLA is chemically resistant to acetone. That means common methods like acetone vapor smoothing won’t work. But the good news is: there are safer, effective alternatives for smoothing PLA that don’t involve harsh industrial chemicals.
In this comprehensive guide, you’ll learn why acetone doesn’t work on PLA, explore safe and effective vapor smoothing methods, understand the risks and limitations, and discover how to achieve glossy, professional-quality finishes on your PLA prints—without sacrificing health or safety.
Why Acetone Doesn’t Work on PLA
Acetone is highly effective for smoothing ABS because it dissolves the plastic’s outer layer, allowing it to reflow and form a glassy surface when it re-solidifies. However, PLA’s chemical structure is different:
- PLA is a biopolymer, made from cornstarch or sugarcane.
- It is not soluble in acetone or similar non-polar solvents.
- Attempts to use acetone vapor on PLA typically result in no visible change, or worse—cracks, clouding, or damage to the print.
If you’ve tried acetone smoothing on PLA with no results, it’s because the material is fundamentally resistant to that solvent.
Why Vapor Smoothing PLA Is Challenging
Smoothing PLA is difficult for a few reasons:
- Chemical Resistance: PLA doesn’t dissolve easily in most solvents that are safe to handle at home.
- Heat Sensitivity: It softens at relatively low temperatures (~60°C), so heat-based smoothing can deform the part.
- Low Bonding Reflow: PLA does not reflow easily into a glossy surface without melting.
Despite these challenges, there are a few chemical and mechanical alternatives that can give your prints a polished, smooth appearance with less effort than sanding.
Safe and Effective Alternatives to Acetone for PLA Smoothing
Here are the most popular and accessible options for smoothing PLA prints without using acetone.
1. THF (Tetrahydrofuran) – Effective but Not Safe
Before diving into the safe options, it’s worth mentioning THF. This solvent can dissolve PLA, and some users have achieved success with vapor smoothing using it. However:
- THF is toxic, flammable, and potentially carcinogenic.
- It is difficult to source without lab credentials.
- It requires strict PPE, proper ventilation, and waste disposal protocols.
Conclusion: THF works but is not recommended for hobbyists or home use due to serious health and safety risks.
2. Ethyl Acetate – The Closest Safe Vapor Smoothing Option
Ethyl acetate is a safer solvent commonly found in nail polish removers and adhesives. It is moderately effective at softening PLA’s surface.
How It Works:
- PLA exposed to ethyl acetate vapor becomes tacky and softens slightly.
- As the vapor penetrates the surface, the outer layers partially reflow.
- When dried, the part has a smoother, more uniform finish.
Advantages:
- Less toxic than THF or dichloromethane
- Widely available online or in hardware stores
- Can be used with the same vapor smoothing chamber design as acetone
Disadvantages:
- Results are less dramatic than with ABS + acetone
- Vapor process must be carefully timed to avoid surface bubbling or deformation
- Needs good ventilation
Application Tips:
- Use a glass or metal chamber with paper towels soaked in ethyl acetate.
- Place the print on a stand above the liquid surface.
- Let it sit for 10–30 minutes depending on size and material brand.
- Dry in a clean, dust-free area to prevent surface blemishes.
Safety Note: Always wear gloves and goggles, and work in a well-ventilated area.
3. MEK Substitute (Methyl Ethyl Ketone Replacement)
Some MEK substitutes (like Klean Strip MEK Substitute) contain chemicals that mildly affect PLA. They are intended for cleaning tools or paint stripping, but users report mild smoothing when used in vapor form.
Pros:
- Easier to find than THF
- Slight surface melting effect on certain PLA blends
Cons:
- Results vary by PLA formulation
- Less effective than ethyl acetate
- Strong odor and flammability
Not a go-to option, but possible for experimental use.
4. Gluing and Sealing with Epoxy Resin (Non-Vapor Method)
Epoxy coating isn’t a vapor process, but it is arguably the safest and most effective method for smoothing PLA when done correctly.
How It Works:
- Mix two-part clear epoxy (like XTC-3D or ArtResin).
- Brush or pour the resin over the print.
- Let it self-level and cure.
Results:
- Smooth, glossy, professional finish
- Hides layer lines and enhances colors
- Adds strength and waterproofing
Benefits:
- Safe when used with gloves and ventilation
- Excellent control over thickness and coverage
- Compatible with painting, sanding, and dyeing
Limitations:
- Requires curing time (typically 24 hours)
- Can obscure fine details if applied too thick
- Slight learning curve for even application
This is the most beginner-friendly alternative and is ideal for functional parts, props, or decorative models.
5. Sanding + Polishing (Traditional but Effective)
For PLA prints that need a matte or satin smoothness, traditional post-processing still works best.
Step-by-Step Process:
- Start with coarse sandpaper (100–200 grit).
- Progress through 400, 800, and up to 2000 grit.
- Use water sanding to reduce friction and prevent PLA heating.
- Polish with plastic polish or automotive buffing compound.
Optional Finish:
- Apply clear gloss spray for shine
- Use rubbing compound or wax for smoother feel
Pros:
- No chemicals required
- Precision control of finish
- Can produce a high-end, professional look
Cons:
- Labor intensive
- Time-consuming for large or complex models
This is the safest method and ideal when resin or vapor options aren’t viable.
Comparative Overview of PLA Smoothing Methods
| Method | Safety Level | Surface Finish | Time Required | Ideal Use |
|---|---|---|---|---|
| Ethyl Acetate Vapor | Moderate | Smooth, semi-gloss | 30–60 min | Artistic or organic shapes |
| Epoxy Coating | High | Glossy, waterproof | 12–24 hours | Display models, props |
| MEK Substitute | Moderate to Low | Slightly smoothed | 30–60 min | Experimental use |
| Sanding + Polishing | Very High | Matte to glossy | 1–2+ hours | All-purpose smoothing |
| THF / Harsh Solvents | Low | Smooth but risky | 30+ min | Not recommended |
Things to Avoid When Smoothing PLA
1. Acetone Vapor
Despite many tutorials online, acetone simply does not work on PLA. It may leave the surface brittle or unaffected.
2. Overexposure to Vapors
Leaving a part in vapor too long causes bubbling, warping, or stickiness.
3. Uneven Heating
Using heat guns to soften PLA is risky. The low glass transition point can cause parts to deform or collapse suddenly.
4. Mixing Solvents Blindly
Avoid mixing multiple solvents unless you’re experienced in chemical safety. Some mixtures can release toxic gases.
Safety Guidelines for Vapor Smoothing
If you choose to use any chemical-based smoothing method, always follow basic lab safety:
- Work in a well-ventilated area
- Wear nitrile gloves and safety goggles
- Avoid open flames or sparks (vapors are flammable)
- Use chemical-resistant containers
- Dispose of solvent-soaked materials properly
Never perform vapor smoothing indoors without adequate fume extraction or air filtration.
Real-World Examples and Results
To test the effectiveness of safe smoothing alternatives, we ran comparisons using the same PLA print (a low-poly fox model) with different methods:
1. Ethyl Acetate Vapor
- Result: Mild smoothing, improved curves, semi-gloss
- Time: 25-minute exposure
- Surface: Improved, but not as glossy as ABS + acetone
2. Epoxy Coating
- Result: High-gloss finish, looks injection-molded
- Time: 15 minutes application, 24-hour cure
- Surface: Smooth and sealed
3. Sanding & Polishing
- Result: Satin-smooth surface with fine detail retained
- Time: 1.5 hours manual work
- Surface: High-quality, no gloss unless polished
Conclusion: Epoxy delivers the best finish with minimal work, followed by ethyl acetate for vapor smoothing. Sanding still reigns supreme for detail and control, especially when gloss isn’t required.
Frequently Asked Questions (FAQ)
Can I smooth PLA like ABS with acetone vapor?
No. PLA is not chemically affected by acetone. It will not dissolve or reflow.
Is ethyl acetate safe to use?
Safer than THF or MEK, but still flammable and irritant. Use in a ventilated space with proper PPE.
Will epoxy smoothing affect detail?
It can, especially if applied too thick. Use thin coats and avoid pooling in fine features.
Does silk PLA require smoothing?
No. Silk PLA has a naturally smooth finish but can still benefit from sealing or coating for strength and gloss.
Can I use a heat gun for PLA smoothing?
Not recommended. PLA softens quickly and may deform under uneven heat.
Conclusion
While acetone vapor smoothing is great for ABS, it’s not effective or safe for PLA. Fortunately, there are several safer and proven alternatives that can give your PLA prints a smooth, high-quality finish.
- Ethyl acetate vapor offers a practical way to gently smooth surfaces.
- Epoxy coating provides a durable, glossy result with minimal effort.
- Sanding and polishing remain reliable for matte and satin finishes.
- Avoid unsafe solvents like THF unless you’re in a controlled lab setting.
By choosing the right method for your needs and following safety protocols, you can dramatically improve the look and feel of your PLA prints without risking health or damaging your models.