Gluing 3D printed parts means joining separate printed pieces with an adhesive, or with a solvent that briefly melts the two surfaces so they fuse. The short answer: use cyanoacrylate (super glue) for close-fitting PLA, PETG and ABS joints, two-part epoxy when the fit is loose or the joint carries load, and solvent welding with acetone only on ABS and ASA. Polypropylene and polyethylene resist almost every glue, so design a mechanical joint instead.
This guide gives a glue-by-material table, the joint shapes that make a glued part stronger and easier to align, the acetone safety data you need before solvent welding, and the finishing steps that hide the seam. Values come from a Loctite data sheet, Gorilla’s epoxy page, Prusa’s chemical smoothing tests and acetone and cement safety data sheets, all linked at the end. Where a number is only a starting point, we say so.
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Gluing 3D prints in six steps
- Dry-fit the parts and fix gaps first: sand high spots, trim support remnants and strings.
- Clean both faces with isopropyl alcohol and let them dry completely.
- Roughen smooth faces lightly with fine sandpaper, especially on PETG.
- Pick the glue from the table below. Test it on a scrap print of the same filament.
- Apply a thin layer to one face (cyanoacrylate) or mix and spread (epoxy), join, and hold or clamp.
- Leave the joint unloaded until the adhesive’s full-cure time has passed, then fill, sand and paint the seam if it needs to disappear.
Which glue for which plastic
| Plastic | Glue that fits | What to know |
|---|---|---|
| PLA | Cyanoacrylate (CA), two-part epoxy | Close-fitting joints suit CA, loose ones suit epoxy. Prusa reports that acetone glued all colors of its Prusament PLA and “works as a superglue”, but that was an observation, not a strength test; try it on scrap first. |
| PETG | Epoxy, or CA after sanding | Reports conflict. PETG resists most solvents, so users on forums describe mixed results with ordinary glues. Roughen the faces and add a mechanical key (slots, pins, a larger overlap). |
| ABS, ASA | Solvent welding with acetone; CA; epoxy | Acetone dissolves the surfaces so they fuse into one piece. This is the one case where a solvent is the standard method. Safety section below. |
| Polypropylene (PP), polyethylene (PE) | Screws, inserts, heat welding; CA with a polyolefin primer | Gorilla’s epoxy page says its epoxy is not recommended for PE and PP. Loctite’s CA data sheet recommends its primer for low-energy plastics. |
| Nylon, TPU, PC, carbon-fiber blends | Check the adhesive maker’s compatibility list | Adhesive data sheets rarely list printed versions of these materials, so test every pairing on scrap. |
Two cautions apply to the whole table. First, an adhesive data sheet describes molded test pieces, not a printed part with layer lines. A joint that outperforms the plastic still fails along a weak layer, which is why print orientation and layer bonding matter (see layer adhesion fixes). Second, the glue is rarely the heat limit: Prusament PLA’s heat deflection temperature is 55 °C according to its data sheet, so a PLA joint softens long before an epoxy rated to about 180 °F does.
Cyanoacrylate (super glue)
Loctite 406, a thin ethyl cyanoacrylate sold for plastics and rubbers, shows what the chemistry does on a plastic that is on the data sheet. At 22 °C and 50 % relative humidity it fixtures (reaches 0.1 N/mm² shear) in under 5 seconds on ABS and 10 to 20 seconds on polycarbonate. After 24 hours its lap shear strength on ABS test pieces is 8.8 N/mm². The sheet does not list PLA or PETG, so treat those as untested for that product.
- **Humidity:** it cures on surface moisture. Loctite names 40 to 60 % relative humidity as the best range; lower humidity cures slower, higher humidity cures faster but may weaken the final bond.
- **Gap:** thin bond lines cure fast, and a larger gap slows the cure. CA is for close fits. Loctite adds that an activator can speed up cure across large gaps but may reduce final strength.
- **Full cure:** the sheet says curing continues for at least 24 hours before full chemical and solvent resistance develops, and suggests waiting 24 to 72 hours before service loads.
- **Application:** apply a small amount to one face and do not spread it with tissue or a brush; assemble within seconds, because there is little time to adjust.
A white haze around a cyanoacrylate joint is a common complaint; use the smallest amount that wets the joint.
Epoxy for gaps and loads
Two-part epoxy is the answer when the parts do not touch evenly or the joint carries load. Gorilla’s 5-minute epoxy page gives a useful set of numbers: apply within 5 minutes of mixing, clamp and leave undisturbed for 30 minutes, then expect a service range of -10 to 180 °F (about -23 to 82 °C). It fills voids, sands, takes latex paint and is rated for outdoor use, but it is not for PE or PP and is not food safe. The page does not state a full cure time, so read the label of your epoxy and allow the stated time before loading.
Mix on a disposable surface, wear gloves, and ventilate; Gorilla’s page asks for both. Roughen the faces first, because epoxy grips a scuffed surface better than a glossy one.
Solvent welding ABS and ASA with acetone
Solvent welding swaps the glue layer for a thin melted zone: acetone softens ABS and ASA, the faces are pressed together, and as the solvent evaporates they harden into one piece. Prusa calls ABS and ASA with acetone by far the most suitable materials for chemical smoothing, and the same solvency is what makes welding work. The method suits parts that fit tightly, because acetone does not fill gaps.
- Dry-fit and clean the faces; sand off elephant’s foot or blobs so they meet flat.
- Work outdoors or at an open window with a fan blowing away from you. Keep flames, sparks and heaters out of the room.
- Brush a thin coat of acetone on both faces, or touch a fine needle or brush to a closed seam and let it wick in. Use as little as works.
- Press the parts together at once, hold or clamp lightly, and wipe squeeze-out immediately.
- Leave the part undisturbed. Prusa found acetone-treated models stay soft for several hours and recommends waiting several hours to a whole day; use that as a starting point before loading a weld.
Gaps are better handled with a thicker mixture of ABS dissolved in acetone, covered in ABS post-processing, and a whole-surface treatment belongs to acetone vapor smoothing.
Acetone safety numbers
The Klean-Strip acetone safety data sheet (rev. 06/2019) is blunt about the risks:
- **Flammable:** flash point 0 °F (about -18 °C, closed cup), explosive limits 2.5 to 13.0 % in air at 77 °F, and vapors heavier than air that can spread along the floor. It warns against use in small enclosed spaces such as basements and bathrooms.
- **Health:** serious eye irritation, respiratory irritation, drowsiness or dizziness. The sheet says that nausea, dizziness, headache or watering eyes mean ventilation is inadequate: stop and get fresh air. OSHA’s limit is 1,000 ppm and ACGIH’s TLV is 500 ppm, both as 8-hour averages.
- **Protection:** wear eye protection and gloves; the sheet states that a dust mask does not protect against vapors and asks for a NIOSH-approved organic-vapor respirator where ventilation is poor. Thin disposable gloves are splash protection at best; check a glove maker’s chemical chart for acetone.
For a deeper look at fumes in a room, see ABS fume ventilation.
ABS cement and solvents we do not recommend
Plumbing ABS cement is a stronger mixture. Oatey’s ABS Medium Black Cement safety data sheet lists 40 to 60 % methyl ethyl ketone, 30 to 40 % ABS resin and 10 to 20 % acetone, with the signal word “Danger”, a highly flammable liquid and vapor, and a warning that it may be fatal if swallowed and enters the airways. Its stated use is joining ABS pipes, not printed parts; read the sheet of the product you buy.
Some older guides, and Prusa’s own chemical smoothing article, name dichloromethane (methylene chloride) for PETG and PLA. We do not recommend it for home use. NIOSH lists it as a potential occupational carcinogen, with an OSHA limit of 25 ppm, and Prusa itself says it should be used only by experienced users with proper protection. Cyanoacrylate or epoxy do the job for PLA and PETG.
Joint design that helps the glue
A butt joint of two flat faces leaves the glue doing all the work. These shapes add area or alignment before any glue is applied:
| Joint | What it adds | Notes |
|---|---|---|
| Butt joint | Nothing | Weakest; use only for light, flat parts. |
| Lap or scarf joint | More bonding area | Leaves a step you will fill and sand. |
| Tongue and groove, dovetail | Alignment and area | Hides the seam line inside the joint. |
| Alignment pins and holes | Exact positioning | Clearance is printer-dependent; see below. |
| Internal rod, magnet, screw or heat-set insert | Strength or reversibility | Add recesses in the model so they sit hidden. |
For pins, a university fab-lab wiki that tests Bambu and Ultimaker machines lists 0.1 to 0.2 mm of clearance for alignment fits on a Bambu printer, while its Ultimaker table starts at 0.2 mm per side and warns that using the tight Bambu value there makes parts stick. Tolerance is added to both sides of a hole, so 0.2 mm per side means a hole 0.4 mm larger. Treat any value as a starting point and print a small test coupon on your own machine.
Two general design rules for layered parts, not data-sheet values: keep the glued faces large and flat, and split the model so glue lines run along layers rather than across a thin stack of them. Orientation guidance is in print orientation for strength.
Hide the seam
Even a good joint leaves a line. To make it disappear:
- Let the glue reach full cure first, so sanding does not tear it.
- Fill gaps and dips with epoxy putty or a filler; build in thin layers rather than one thick one.
- Sand flush with a progression of grits: the sanding guide has the sequence and the dust precautions.
- Spray a filler primer to show remaining flaws, repair them, and repeat; see primer and filler for the details.
- Paint over the primer. A seam that is hidden under paint only needs to be level, not invisible.
Common gluing problems
| Symptom | Likely cause | Fix |
|---|---|---|
| Joint peels off cleanly | Dirt, finger oils or a low-energy plastic (PETG, PP) | Clean, scuff, add a key; use primer or screws for PP |
| Part breaks beside the glue line | The layers failed, not the glue | Change orientation or settings; see layer adhesion |
| White haze around a CA joint | Too much glue or very humid air | Apply less; sand and polish the haze off |
| Parts shift while curing | Fast CA or no alignment features | Add pins; use slower epoxy for large parts |
| Welded ABS joint looks wet or deformed | Too much acetone or loaded too early | Use less; wait longer before handling |
| Glue will not hold on a flexible print | Rigid glue on flexing material | Test a flexible adhesive on scrap; add mechanical fixing |
Frequently asked questions
What is the best glue for PLA 3D prints?
Cyanoacrylate is the usual first choice for close-fitting PLA joints because it fixtures in seconds. Use two-part epoxy when the faces do not meet evenly or the joint carries load. Clean and lightly roughen both faces, and allow the full cure time before loading.
Can you glue PETG, and does acetone work on it?
PETG can be bonded with epoxy or CA, usually after sanding the faces, but it resists most solvents and reports on results vary, so test on scrap. Acetone does not dissolve PETG. Add slots, pins or a larger overlap so the joint does not depend on the glue alone.
Does acetone glue PLA?
Prusa reports that acetone glued all colors of its Prusament PLA together and “works as a superglue”, but also found it a poor way to smooth PLA, and acetone vapor exposure cracked PLA parts. Treat it as a light-duty trick, not a strength method. Cyanoacrylate and epoxy are safer and better documented choices.
Is it safe to weld ABS with acetone indoors?
Acetone is highly flammable (flash point 0 °F) and its vapor can cause dizziness and eye and airway irritation, so work outdoors or with strong cross-ventilation and no ignition sources. The safety data sheet says a dust mask does not stop vapors and that dizziness or headache means the ventilation is inadequate. Keep the amount small and the container closed.
Sources
- Loctite 406 technical data sheet (Henkel, copy dated 2018)
- Gorilla Epoxy product page: set time, clamp time, service range, limits
- Prusa Research: Improve your 3D prints with chemical smoothing
- W. M. Barr Klean-Strip acetone safety data sheet, revision 06/2019
- Oatey ABS Medium Black Cement safety data sheet
- NIOSH Pocket Guide: methylene chloride
- Prusament PLA technical datasheet (heat deflection temperature)
- UAL Digital Fabrication Lab wiki: clearance and tolerance
