Gluing a magnet to PETG: This method really works
For most PETG applications, embedding during printing or using a two-part (2K) epoxy adhesive are the most reliable methods for permanently attaching a neodymium magnet. Super glue often fails on PETG after just a few weeks outdoors. It is recommended to use mechanical anchoring plus epoxy if a cache container is expected to withstand the elements.
In short:
- For the permanent attachment of magnets to PETG, embedding during printing or using 2K epoxy is the most reliable method, whereas super glue only provides short-term adhesion.
- Mechanical press-fitting during printing is considered the most robust solution, as there is no glue line to fail and no solvent to degrade the connection.
- When gluing, thorough surface preparation is recommended, including cleaning, sanding, and degreasing, as well as using a UV- and moisture-resistant 2K epoxy adhesive.
- Magnet sizes and shapes should be chosen based on the intended use, with additional mechanical safeguards like screws or coatings improving outdoor durability.
- Protective layers such as epoxy or PTFE coatings significantly increase corrosion resistance in outdoor environments, especially for coated or embedded magnets.
Table of Contents
- Which method holds magnets best on PETG?
- Guide: Gluing magnets to PETG with 2K epoxy
- Embedding during printing: Mastering magnet inserts in the slicer
- Magnet selection: Size, shape, and how much strength really matters
- Corrosion protection and coatings: What really lasts outdoors
- Common magnet gluing problems and how to fix them
- CacheWerk practice: Proven approaches and product examples
- Author's view: Why embedding is almost always worth it
- CacheWerk products that make installation easier
- Sources
- FAQ
Which method holds magnets best on PETG?
Not every adhesive is compatible with PETG. The material is chemically quite resistant, which is good for longevity but also causes many common adhesives to simply bead off. To permanently attach a magnet, you should first know which methods actually function reliably.
Super glue (cyanoacrylate) is the most obvious choice because it cures quickly and can be found at any hardware store. However, on PETG, it often forms only a thin, brittle connection that cracks with temperature changes or moisture. For a geocache hiding spot that hangs outside for months, this is insufficient.
2K epoxy adhesive performs significantly better. It fills small gaps between the magnet and the component, tolerates temperature fluctuations, and remains stable even when wet. This is exactly why we recommend 2K epoxy for almost every outdoor application where a magnet must be firmly connected to PETG.
Mechanical press-fitting during the print is the third option and, in many cases, the most robust one. The magnet is integrated directly into a pocket in the component by pausing the print and then resuming it. There is no glue line to fail and no solvent to degrade the connection over the years.
Which method is suitable for you depends on the project:
- Super glue: only suitable for short-term tests or indoor applications without load.
- 2K epoxy: the best choice for post-print gluing in outdoor projects and varying temperatures.
- Press-fitting during printing: ideal when the part is being designed from scratch and the magnet can be accounted for from the beginning.
- Mechanical mounting (screw, countersink, heat shrink): useful if the magnet needs to remain replaceable later.
A screw connection with a countersink is a good option if the magnet needs to be replaced eventually, for instance, if it loses strength or corrodes. Heat shrink tubing over the magnet provides additional protection against scratches and minor rust, though it does not replace a firm bond. If you want the best of both worlds, press-fit the magnet mechanically and secure it additionally with a drop of epoxy. This takes a few minutes more but lasts much longer than any individual solution.
Guide: Gluing magnets to PETG with 2K epoxy
If you choose epoxy, do not underestimate the preparation. The bonding surface determines success or failure, not the brand of glue.
- Cleaning: Wipe the bonding surface with isopropanol to remove release agents, grease, and print dust.
- Sanding: Sand the surface with 80 to 240 grit sandpaper so the adhesive can mechanically grip.
- Degreasing: Wipe again with isopropanol, as fingerprints are enough to weaken the adhesion.
- Product selection: Look for a 2K system with specified UV and moisture resistance, such as Spabond 435 from Gurit, which is designed for structural bonding with clear mixing ratios.
- Mixing: Follow the mixing ratio of the two components specified in the data sheet exactly.
- Application: Apply the adhesive thinly and evenly to both surfaces, magnet and PETG.
- Positioning: Place the magnet with light pressure and align it immediately; epoxy is difficult to correct once it has set.
- Fixing: Weigh the magnet down or clamp it until the curing time specified in the data sheet is reached.
- Testing: Once fully cured, test the adhesion with light lateral pressure—never test with full force immediately after gluing.
- Sealing: For outdoor use, optionally apply a thin additional layer of epoxy over the edge of the magnet to keep moisture out.
Pro Tip: Never glue at temperatures below 15°C (59°F); otherwise, the epoxy will cure incompletely and remain permanently tacky instead of hard.
Embedding during printing: Mastering magnet inserts in the slicer
Integrating the magnet directly during printing saves you from gluing entirely and results in a mechanically more stable connection. The trick lies in the right fit and a controlled pause moment.
- Plan the pocket with about 0.1 to 0.2 millimeters of clearance so the magnet fits tightly but without force.
- Use a pause function in the slicer at the appropriate layer height, insert the magnet, and let the print continue.
- Before inserting, ensure the nozzle itself does not react magnetically; otherwise, it will pull the magnet out of position as it moves.
- Slightly reduce the print speed over the insert zone so the new layer fuses better with the inserted magnet.
- For a closed pocket, choose at least two to three solid perimeter layers as coverage; a single thin layer offers little protection and virtually no hold.
- When using magnetically filled filaments like Prusament PETG Magnetite, keep in mind that a print temperature around 270°C and a hardened steel nozzle are necessary, as the material is abrasive due to the filler.
If you want to avoid gluing entirely, print the pocket so that the magnet is completely enclosed by the PETG. This simultaneously protects it from moisture and corrosion, though it cannot be replaced later.
Magnet selection: Size, shape, and how much strength really matters
The holding force of a magnet stated on the packaging is usually measured under laboratory conditions: two flat steel surfaces, direct contact, no intermediate layer. In practice, there is almost always a thin layer of paint, rust, or the glue line itself between the magnet and the counter-surface, which noticeably reduces the real holding force.
For a geocache hiding spot, the pure pull force perpendicular to the surface is rarely the only benchmark. Wind, contact by finders, or slight shifting create lateral shear forces, against which a magnet holds significantly less effectively than against direct pull. Therefore, a safety margin is worth it: Choose a magnet that, according to the data sheet, provides at least twice as much pull force as the actual weight of the container including its contents.
Typical sizes for common cache formats:
- PETling cap: small disk magnets with a diameter of a few millimeters are usually sufficient, as the container weight is low.
- Nano cache: tiny magnets, often with a hole for additional securing, because space is extremely limited.
- Small cache with hanger: stronger magnets with a countersink so a screw secures the connection in addition to the adhesive.
Magnets with a hole or countersink are almost always the better choice for outdoor use compared to smooth disk magnets, as they allow for a second, mechanical safeguard.
Epoxy-coated magnets show significantly improved corrosion resistance compared to uncoated variants in overview studies on bonded NdFeB magnets, which is relevant for caches mounted outdoors permanently.
Corrosion protection and coatings: What really lasts outdoors
A neodymium magnet without a protective coating rusts surprisingly quickly once moisture reaches the base material. For a hiding spot that hangs in the woods or on a wall for months, the coating is almost as important as the gluing method itself.
The common coatings differ significantly in moisture resistance and abrasion behavior:
| Coating | Moisture Resistance | Abrasion Sensitivity |
|---|---|---|
| Ni-Cu-Ni (Standard) | Moderate, prone to issues if scratched | Relatively robust against mechanical abrasion |
| Epoxy coating | High, protects even if slightly damaged | More sensitive to sharp scratches |
| PTFE coating | High, additionally chemically resistant | Very robust, low-friction |
An overview study on corrosion protection for bonded NdFeB magnets describes epoxy coatings and composite covers as a promising approach against corrosion, though these layers are mechanically more sensitive than pure metal coatings. For geocaches, this means: An epoxy cover is worthwhile primarily if the magnet is additionally placed in a protected cavity and is not directly exposed to weather or frequent contact.
If you want to play it safe, combine both approaches. The standard Ni-Cu-Ni magnet is additionally covered with a thin epoxy layer and then embedded in a PETG pocket, which itself already takes on part of the weather protection.
Common magnet gluing problems and how to fix them
Most gluing problems on PETG can be traced back to two causes: an inadequately prepared surface or the wrong adhesive for the application.
- Magnet detaches after a short time: usually due to a lack of sanding the bonding surface; simply sand and reglue.
- Bubbles in the glue: often caused by applying epoxy too thickly; apply it thinner and distribute more evenly.
- Magnet loses holding force: indication of incipient corrosion; replace the magnet and choose a coated variant in the future.
- Bond fails in cold weather: curing occurred below the minimum temperature; repeat under warmer conditions.
A simple weight test is sufficient for verification: Hang a defined weight from the glued magnet and observe if it still holds after a few minutes. Additionally, a lateral friction test, in which you carefully push the magnet across the bonding surface, simulates the real shear forces in use.
Pro Tip: Keep strong neodymium magnets away from credit cards, pacemakers, and electronic devices while working, as they can delete data or interfere with electronics.
CacheWerk practice: Proven approaches and product examples
PETG is often used because the material offers a good balance of stability and weather resistance for geocache hiding spots. For surface finishing after printing, we have compiled practical notes on wet sanding and finishing PETG parts, which can be applied directly to glue preparation.
In practice, a simple rule has proven effective:
- Press-fits with slight clearance hold better long-term than pure glued connections without mechanical support.
- Pre-assembled magnet holders can save hobbyists the preparation steps that post-print gluing requires.
- Weatherproof housings reduce the load on the magnet itself because less moisture reaches the glue line.
If you are planning your own PETG hiding spots, you can find further details on print parameters and design decisions in our guide on PETG geocache hiding spots, which directly impact the durability of the magnet attachment.
Author's view: Why embedding is almost always worth it
I prefer embedding during printing whenever possible because a mechanical connection does not undergo aging like an adhesive. I only reach for 2K epoxy if an existing component requires a magnet as an afterthought.
If you want to test, compare three magnet sizes on a test body, measure the holding force with a simple spring scale, and store the sample outside for several weeks. Community experiences from geocaching forums often add details to such tests that are not noticed in the lab.
— Benedikt
CacheWerk products that make installation easier
If you want to save yourself the work of gluing, you can find ready-made solutions with us. The Geocaching PETling with magnet holder comes in camouflage and signal colors and includes the magnet holder directly, without the need for any gluing of your own.
The Geocaching screw cap with eyelet for PETlings is suitable if you are looking for a hangable hiding spot without an additional magnetic mount; it is robust, weatherproof, and comes in a pack of two. And for those looking for a nano-format with a built-in secret compartment, the screw-top stash with secret compartment and magnet offers exactly the combination of mechanical security and magnetic attachment that we recommend in this article. All three products save you the preparation steps from the guide above and are ready for immediate use.
Sources
- Prusament PETG Magnetite 40% — Prusa Help
- Recent Advances in Corrosion Inhibition of Bonded NdFeB Magnets — Materials (2024)
- Spabond 435 — Gurit Product Data Sheet (PDS)
FAQ
How can I glue magnets to plastic?
Clean the surface with isopropanol, roughen it with 80 to 240 grit sandpaper, and then apply a thin, even layer of 2-component epoxy adhesive such as Spabond 435. Fix the magnet in place until fully cured; superglue is usually insufficient for permanent bonds.
What material does a magnet stick to?
A magnet adheres directly to ferromagnetic materials such as steel or iron, but not to PETG or other plastics themselves. On plastic, the magnet is therefore embedded mechanically or fixed with a suitable adhesive, such as 2-component epoxy.
Do magnets work through plastic?
Yes, the magnetic field penetrates plastic almost unimpeded because PETG and most other plastics do not provide magnetic shielding. This is why PETG walls between two magnets or between a magnet and a steel surface work without any issues, as long as the wall thickness is not too great.
How can you insert magnets into 3D prints?
The most reliable method is a pause in the slicer at the appropriate layer height, during which the magnet is inserted manually before the print is resumed. Plan the pocket with a tolerance of about 0.1 to 0.2 millimeters and at least two to three perimeter layers for coverage to ensure the magnet sits firmly and remains protected.
Which glue is best for PETG?
2-component epoxy adhesive is considered the most reliable choice for PETG because it fills gaps and tolerates temperature fluctuations and moisture well. While superglue is faster, it often only holds temporarily on PETG and is hardly suitable for outdoor applications.