Working on finishing FDM prints at home can turn rough, layer-marked parts into smooth, glossy creations. By using techniques like careful sanding, coatings, or heat, hobbyists can achieve a “glass-like” smooth surface even on PETG or PLA prints. This guide covers practical, beginner-friendly methods to smooth PLA and PETG 3D prints, comparing what works (and what doesn’t) and including safety tips and product ideas along the way.
Safety First: Gear and Workspace
Before any post-processing, prioritize safety. Always work in a well-ventilated area (open windows or use a fan), and keep fire sources far from flammable solvents. Wear protective equipment:
chemical-resistant gloves, safety goggles, and at least an organic-vapor respirator when handling smoothing agents or epoxy.
- Ventilation & PPE: Ventilate well. Wear nitrile or neoprene gloves, eye protection, and a respirator with organic-vapor cartridges for any solvents or epoxy.
- Fire safety: Keep any liquids (acetone, MEK, etc.) away from sparks or flames – they are highly flammable.
- Dust protection: Even sanding creates fine plastic dust. Use a dust mask or respirator when sanding larger parts.
A neat, covered workspace (plastic or cardboard under your project) and good lighting will also help prevent accidents and mistakes.
Sanding: The Safe Workhorse
Sanding is the simplest way to smooth PLA or PETG without chemicals. By gradually abrading away the outer layer, you can eliminate most visible lines. Start with a coarser grit to knock down the peaks, then move to finer paper to polish the surface.
For example, you can:
- Start around 200–400 grit to remove major steps and layer ridges.
- Move through 800, 1000, and up to 2000 grit for a glassy finish.
- Use wet-sanding (with water) in the finer grits to avoid clogging and overheating.
Useful tools for sanding:
- Assorted sandpaper kit: multi-grit wet/dry sandpaper set (e.g. 200–2000 grit).
- Sanding block or sponge: Keeps the paper flat and helps follow curves.
- Water and cloth: For wet-sanding and wiping down between grits.
- Polishing compound: a fine plastic or car polish can add extra shine at the end. Plastic polishing compound.
Work patiently in smooth circular motions. After sanding, wipe the print clean; it should already look much smoother. For a mirror-like sheen, use a soft cloth or buffing wheel with polishing compound on the final high-grit surface. Remember that sanding removes material, so very thin features may become slightly smaller.
Chemical Smoothing: What Works (and What Doesn’t)
Chemical vapor smoothing uses solvents to melt just the surface of the plastic. Some plastics (like ABS) respond very well to common solvents, but PLA and PETG are tougher. Here’s a quick rundown of what is and isn’t worth trying at home.
Acetone
Skip it for PLA and PETG. Acetone vapor works wonders on ABS, but PLA resists it. On PLA, acetone tends to leave the surface rubbery and sticky, ruining the finish instead of smoothing it. PETG also isn’t properly smoothed by acetone. So do not try a classic ABS-style acetone bath on PLA or PETG prints.
Ethyl Acetate
Ethyl acetate is a much better choice for PLA (and sometimes PETG). It’s found in some “non-acetone” nail polish removers and citrus-based solvents. Used as a vapor, it can rapidly smooth PLA surfaces.
Basic DIY vapor method:
- Put a small amount of ethyl acetate on paper towels in a glass or solvent-safe plastic container.
- Hang or place the print above the towels – do not let it touch the liquid.
- Seal the container and watch closely for a few minutes as fumes soften the surface.
- When layer lines start to blur, open the container and let the print air out completely.
This method can yield a very smooth finish, but only if done with strict safety: full PPE (gloves, goggles, respirator) and good ventilation. Always practice on a scrap piece first.
MEK, THF & DCM
Methyl ethyl ketone (MEK), tetrahydrofuran (THF), and dichloromethane (DCM) can dissolve PLA (and PETG) very quickly. They are also extremely flammable or toxic and are not recommended for casual home use. They belong in well-equipped workshops or labs, not on a hobbyist’s kitchen table.
Caustic Soda (Lye)
Sodium hydroxide (lye) in water can slowly etch PLA and remove some materials. It does smooth the surface over time, but it’s highly corrosive and dangerous to handle. Only consider lye if you are experienced with it, have full safety gear, and can work outdoors or with a proper fume setup.
For PETG, there’s no simple, safe “magic solvent” like acetone for ABS. PETG is more often smoothed by heat or coatings rather than DIY solvent baths. Ethyl acetate can soften PETG slightly, but the effect is subtle compared to PLA.
Epoxy Resin Coating (and Primers)
A foolproof way to hide layer lines is to coat the print in a smooth material. The most popular option is a brush-on two-part epoxy resin. The resin flows into the grooves of the layers, then cures into a hard, clear shell.
One well-known product is Smooth-On XTC-3D, but many similar clear epoxies work.
- Epoxy resin kit: brush-on epoxy resin for 3D prints.
- Application tools: disposable mixing cups, stir sticks, and foam or bristle brushes.
- Safety: wear gloves and work in a ventilated area. Uncured epoxy can irritate skin and lungs.
Mix the resin and hardener according to the instructions (often 2:1). Apply a thin, even coat with a brush. Avoid big drips or pools. You usually have around 10–15 minutes of working time before it starts to stiffen. Pop any bubbles with a pin or gently warm the surface with a hairdryer on low.
Let the first coat cure fully in a dust-free place. If needed, lightly sand and add a second coat. Two thin coats are often enough for a glossy, smooth finish. You can even wet-sand the cured epoxy to 2000+ grit and polish it for a true mirror surface.
Keep in mind that epoxy adds a small thickness (often less than 1 mm). Avoid using it on parts where dimensions are critical. Once cured, epoxy is permanent, so double-check your print before coating.
Primer Alternative
If you plan to paint the model, spray primers or automotive filler primers can also smooth out prints. After light sanding:
- Spray 2–3 thin coats of a plastic/filler primer.
- Let each coat dry, then sand again with fine grit.
- Repeat until layer lines are mostly gone.
Primers are much safer than strong solvents; just wear a mask and work in a ventilated space.
Heat Gun and Polishing
A heat gun can be a quick way to reduce visible lines on some prints. Used carefully, it softens just the top surface so the plastic reflows slightly and looks smoother.
- PLA: use the lowest heat setting (around 50–70 °C). Keep the gun moving and at least 10 cm away. PLA can warp easily if overheated.
- PETG: use a medium-low setting (~85 °C, around PETG’s glass transition). Work evenly over the surface and avoid staying too long in one spot.
Overheating will deform the geometry, so always test on a scrap first. Heat smoothing is best for larger, simple surfaces rather than fine details.
After your main smoothing method (sanding, epoxy, primer, etc.), a final polishing step can make the surface really shine. Use a plastic polishing compound or fine car polish with a soft cloth or buffing wheel. Rub in small circles until the print gleams. A final clear coat (spray lacquer or varnish) can also add gloss and protect the surface.
Tools for Heat & Polish
- Heat gun: an adjustable-temperature hot air gun. Craft or DIY heat gun.
- Polishing compound: plastic or automotive polishing compound.
- Soft cloth or buffing wheel: for applying polish and buffing the surface.
Summary of Methods
- Sanding is the safest and most accessible way to smooth PLA or PETG. It takes time, but no chemicals are needed.
- Chemical vapor with ethyl acetate can quickly smooth PLA (and slightly PETG) if done with strict safety. Acetone does not work on PLA.
- Epoxy coating fills in lines and gives a glossy finish, great for display models.
- Primers/sprays are a middle ground: easy to use and sandable, ideal if you plan to paint.
- Heat gun can polish large surfaces, especially on PETG, but overheating can damage parts.
- Polishing (buffing compound) is the final touch for that mirror shine.
Choose based on your project: for rugged parts, sanding might be enough; for showpieces, combine sanding, epoxy, and polishing. Many beginners sand first, then apply a coat of epoxy resin for gloss, then do a final polish. Each extra step costs time and materials, so weigh the effort against how perfect you need the finish.
Recommended Supplies (Amazon)
For convenience, here are the kinds of items you can find on Amazon EU to help with post-processing:
- Multi-grit wet/dry sandpaper kit (200–2000 grit).
- Sanding blocks/sponges for curves and edges.
- Chemical-resistant nitrile gloves for solvents and resins.
- Respirator mask with organic vapor filters.
- Safety goggles to protect your eyes.
- Epoxy resin kit (such as XTC-3D style brush-on epoxy).
- Disposable mixing cups & brushes for epoxy.
- Heat gun with adjustable temperature.
- Plastic polishing compound or fine buffing paste.
- Primer spray (plastic/filler primer for models or automotive use).
- Miscellaneous: mixing sticks, paper towels, plastic sheet to protect the table, and a pin for popping bubbles.
These products all have European versions or shipping (look for Amazon’s EU sites). Investing in proper gear makes the job easier and safer. For example, a respirator and gloves let you safely try vapor smoothing or work with epoxy, and a fine-grit sandpaper set is indispensable for any finishing work.
Final Tips
Improving print surfaces is a step-by-step process. Always start with the gentlest method (like sanding) and work your way up. Test techniques on a scrap or a hidden area first. Keep your expectations realistic – perfectly smooth, shiny prints take time and patience.
In the end, combining methods often yields the best results (for example: sand → resin coat → polish). And remember: always prioritize safety and ventilation. With care and practice, you can make your PLA and PETG prints look professional – and even shiny – without leaving your home workshop.