Lakeside Pottery is a ceramic, sculpture and Kintsugi repair and restoration facility.
Many ask for advice and one of the most common questions is "Can I use Super or Crazy Glues to fix my broken ceramic or sculpture? How do I choose? Its so much easier than 2-part epoxies!" There is a misunderstanding about the difference between super glues and epoxy and they are therefore sometimes used interchangeably but, super glues and epoxy adhesives are different and have specific purposes.
Should Epoxy or Super Glue be Used for Ceramic or Sculpture Repair?
It is important to answer this question before you attempt to repair a broken item that might be valuable.
1) What are the attributes of these glues?
2) What problems might these glues present?
3) What else do you need to know about these adhesives for repairing broken pottery, ceramic, stone or china?
Epoxies have a strong bond, strong structural strength and are better at filling voids between parts. Epoxy consists of two parts, the hardener and the resin that must be combined and mixed well. In some brands, the resin and the hardeners are different colors. Mixing the two generates a third color that can tell you when the two parts are properly mixed. Epoxies come in different sizes, names, containers, and squeezing styles. Different epoxies have different purposes – mending, filling, and protective coating. In this write-up, well focus on mending epoxies only as compared to super glues.
Super glues are a single component made from Cyanoacrylate that hardens rapidly with a strong bond when exposed to moisture in the air. It is a very thin watery liquid that can be used directly out of the bottle without mixing. However, Super glues have very low shear strength (side push or pull) which means that the parts bonded will resist direct pulling but not off-angle stress. Super glues require a tight fit given the liquidity and very thin glue layer between the broken parts for proper bonding and therefore will not fill in voids. Super Glues work best on non-porous materials.
Lastly, Super glues effects subsequent layers of restoration such as fillers or paints used for implementing a seamless repair. With time, it will interact with this layer and will appear in a different color like the example on the right.
Super glue interacting with repair layers (e.g., paint)
Cementing and Filling in Gaps Unlike super glues, mending epoxies are also gap fillers given the thickness of the parts mix. If the broken pieces do not have a perfect fit, epoxy will fill in the gaps while creating a bond between the broken pieces.
2-part even ratio mix
Epoxies Setting Time Epoxies are available for different set and cure time and can vary from minutes to several hours. Therefor, holding the cemented parts in place until the epoxy sets can be a challenge. This time depends upon the chemical composition of the hardener. You will want to consider whether quick setting or slow setting epoxy is the most appropriate for your project.
Holding the cemented pieces by hand waiting for the duration of the cure time is not practical or accurate. We have created a tutorial illustrating some methods of keeping cemented segments safely in place while waiting for the adhesive to cure. See link or click on photo on right.
Mixing 2-part epoxy
Keeping pieces in place while waiting
When to use slower setting epoxy?
If you are working on small items that can be secured quickly, the quick setting 5 minute epoxy may be your choice. Spreading glue over larger items may require slower setting of product. Five minutes go by fast! Slower setting epoxy is generally stronger, although some brands have recently improved the strength for fast setting epoxies to be as good.
Applying 2-part epoxy
High Temperature Failure Superglues are fairly resistant to heat, but their strength will be reduced. It is not recommended for applications where the glue may be exposed to temperatures over 200 degrees F. The bond will deteriorate with heat..
Most epoxies can withstand temperatures up to 200° F (90° C). Anything higher and the molecular structure will change, causing the epoxy to soften.
Cover full surface
Repair Line Thickness and Color Super glues leave a thinner mending line while some epoxies have color; some are clear and others are yellow, but they all leave a thicker line. Therefore, consider appearance in your selection of epoxy. If further restoration is planned, (i.e. hiding repair lines with fillers, colors and cold glazes), select the stronger epoxy regardless of color.
Place and apply pressure
Note: Lakeside Pottery Studio uses 3600 PSI clear epoxy (see link) for most mending applications. Most clear mending epoxies do yellow with time when exposed to UV light (e.g., sun or fluorescent light) and can impact the quality of the over-painting restoration effort.
Removing epoxy later
Cleaning We recommend not to attempt cleaning excess epoxy while it is still liquid to avoid lining shift and smearing on to a larger surface area. Let the epoxy cure partially to ensure a stable bond before removing excess cured epoxy with a blade (see more). Epoxy spillover on soft ceramic (e.g., terra cotta) is undesirable. In removing the excess epoxy you will likely scratch soft ceramic or stone and cause further surface damage.
Conclusion Lakeside Pottery Studio does not use super glues for ceramic or sculpture repairs. Super glues are just not strong and durable enough and are not suitable when used with a seamless repair given their interaction with other materials such as fillers and paints.
In most of our ceramic restoration, we invest significant effort in hiding the repair and therefore have to make sure the mending longevity and visual performance are the best possible and will last indefinitely.
We use high-end, non-yellowing 5 minute clear epoxies (see link for the brand we do use) in most ceramic, stone and Kintsugi repair applications.
Super glues are probably a good choice for items that are not handled often, without long life expectation and subsequent layers of other materials are not applied over the mending areas.