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As this is the last lesson in this class, I thought it would be fun to combine a repair and a creative project into one. Also, we are going to break a bunch of ceramic bowls :D

But first, let's go over what Epoxy is, what it's commonly used for, and how to remove it.

Epoxy refers to a class of adhesives, plastics, and paints made from synthetic thermosetting polymers containing chemical epoxide groups. Using epoxies consists of combining two starting compounds - resin and hardener. The resin is mixed with a specific hardening catalyst to begin a curing process, and can turn a goopy resin into a rigid plastic in 5 minutes to an hour, depending on your chemical ratio.

Two part epoxy glues are used in all kinds of projects. The are often equivalent to, or stronger than, metal fasteners like screws or nails.

Here are some great reasons to choose an epoxy adhesive:

  • Your parts need to stand up to lots of vibration or chatter
  • The project you need to glue is regularly exposed to high temperature
  • You need to accomplish some gap filling - like over drilling a hole in wood
  • Needing to permanently bond dissimilar surfaces, like wood to plastic.

Tips and Facts

Mixing the Resin and Hardener

To demonstrate how to mix and apply epoxy resin, we are going to affix some saw-tooth mounts to the shelves from our White Glue Lesson.

Squeeze equal amounts of resin and hardener onto a dust-free, sturdy, disposable surface. Scrap cardboard or a paper plate works perfectly, but you can also use a silicone mat, the resin will not bond to that.

To mix the resin, cut the end off a popsicle stick or tongue depressor. This way you have a flat edge scraping as much of the resin off your flat surface with each pass of the tool.

Push the mixture around for about a minute, you can feel it starting to gel as you mix. When the mixture barely drips from the mixing stick it is ready for use.

It is best to prepare as much as you think you can use within the epoxy's specified set time. If you need to apply a large amount of glue to a broader surface area, it is best to work with epoxies with a longer or extended open time. You want to give yourself enough time to mix your adhesive as well as clamp/jig/nest your parts properly.

Applying the Adhesive

Apply the mixture to the surfaces that are going to be bonded. Join surfaces and clamp/jig your pieces until the bond sets. The set time is indicated on the packaging of the epoxy. On average it will cure to full strength 4x longer than the set time. So if it is 5-minute set epoxy it cures to strength in 20 minutes, if you have 30-minute epoxy, it cures to strength in 2 hours. Full cure takes 24-72 hours depending on the resin/hardener formulations.

Example

Using 5-min epoxy, I applied the gelled mixture to the sawtooth mounts. I mixed the epoxy for a little over a minute and let it sit for another minute until the viscosity suited the spread and flow I believed necessary to cover the back of the saw-tooth mounts joining points without overflowing the edges or being too overworked to apply.

Temperatures

Epoxy is another adhesive that is quite sensitive to temperature swings, it effects the handling properties of uncured epoxy and its rate & degree of cure.

Mixing an epoxy resin and hardener together starts an exothermic chemical reaction, meaning it produces heat. Warmer temperatures accelerate this reaction while cooler temperatures slow the reaction.

Ambient temperature can also drastically change epoxy’s viscosity or thickness. As the temperature drops, epoxy becomes proportionally thicker, reducing its ability to flow and spread and penetrate bonding surfaces. Mixing resins in cold temps may result in air bubbles being introduced into your mixture and then held in suspension after curing. A good bond is a bubble-free bond.

You can combat this by working in a well-ventilated area that has a consistent temperature. I regularly work in my underground garage with fans pointed out the window and have had pretty consistent results.

Once you get a feel for working with this adhesive you'll begin to sense when a good time is to start applying the epoxy to your bonding surface. It shouldn't be too runny or too rigid. Epoxy is really the goldilocks of glue, everything needs to be just right for to produce the perfect bond.


Removal

Like almost every other adhesive, you can remove uncured epoxy with brute force and solvents. Scrape as much material as you can from the surface using a stiff metal or plastic scraper. Try using a heat gun on the uncured epoxy to lower its viscosity and remove a thinner adhesive. After removing as much as possible, the remaining residue can be removed with lacquer thinner, acetone, or alcohol.

Once the epoxy is cured, you'll have to remove it mechanically. Sanding, chipping, smashing....it's gonna take some effort. This stuff turns from goo into a super-hardened plastic, so do your best to apply precisely and be sure to wear plenty of PPE!

If you really need to get a coat of epoxy off a surface, you can use a heat gun to soften the epoxy. Heat a small area and use a paint knife or cabinet scraper to remove the bulk of the coating. Be sure to work in space with lots of ventilation when heating epoxy, it can off-gas quite a bit. Sand the surface to remove the remaining material.

I said this in our Rubber Cement lesson, but it's worth repeating: NEVER heat an area you have recently applied solvents on. Most solvents are quite flammable and applying heat to them has the potential to ignite a chemical fire.


Captsone Project

Sometime last year, I heard about a process called Kintsugi - a Japanese tradition of repairing broken ceramics with gilded lacquer. The point of kintsugi is to illuminate the history of an object. So you broke a great utilitarian object like a bowl? An illuminated repair like seen in the kintsugi process highlights the cracks as an event in that objects life, and highlights the cracks and the repair with a wonderfully gold glue, instead of just junking it after it breaks. I was inspired by this concept and wanted to make a whole bowl set for my house using this technique. For this capstone project, we are going to emulate this tradition with slowish-setting 15-minute 2-part epoxy, and gold pigment powder.

Materials Needed:

Start by placing the ceramic piece into a zipper bag. Close the bag, and break the bowl. Get creative, throw it at the floor, use a hammer, channel your inner Hulk. Breaking the pieces in a bag ensures that you don't have any pieces flying willy-nilly.

Pull the pieces out of the bag and establish an assembly order, begin mixing the adhesive.

Measure out equal parts of hardener and resin, and add a half-dime-sized amount of pigment powder.

There are all kinds of epoxy pigments available, some are powdered, others come in gel resin form. If you use a gel pigment, be sure to use a little bit more hardener when you are mixing the resin. I like working with powdered pigments because you don't have to compensate by adding more hardener, but gel pigments are often more opaque.

Gently dab adhesive on to the borders of the crack. Ceramic is very sharp, I recommend handling this project with gloves that won't rip or tear, but also can form a chemical barrier to protect your skin.

Use enough epoxy adhesive to create a raised bead along the fracture line. This ensures that when you fit your pieces together, some of the gold enamel will squeeze out the sidses.

Jig pieces as necessary. The curebox is handy again here, but we have to make sure the broken pieces nor the adhesive comes into contact with the rice. You can use parchment paper spritzed with some cooking spray(or mold release) to act as a protective barrier from the grain as the glue cures.

Fill in any outstanding gaps with epoxy. Allow to cure completely for at least 24 hours before using. I love using this bowl set around my house. They all started as uniform white plain bowls, but now each one has gilded imperfections unique to each vessel.

That was fun, right?! This was the last adhesive covered in this glue class, but the wrap-up lesson has some great tips and facts to remember, as well as some super inspiring projects. You're almost done!


Quiz

{
    "id": "quiz-1",
    "question": "Epoxy creates an endothermic reaction as it cures.", 
    "answers":[
        {
            "title": "True",
            "correct": false
        },
        {
            "title": "False",
            "correct": true
        }

    ],
    "correctNotice": "That's correct",
    "incorrectNotice": "That's incorrect"
}
{
    "id": "quiz-2",
    "question": "The set time is the same duration as the cure time for epoxy",
    "answers":[
        {
            "title": "True",
            "correct": false
        },
       {
            "title": "False",
            "correct": true
        }

    ],
    "correctNotice": "That's correct",
    "incorrectNotice": "That's incorrect"
}
{
    "id": "quiz-3",
    "question": "A good epoxy bond has...",
    "answers":[
        {
            "title": "Lots of bubbles trapped inside",
            "correct": false
        },
        {
            "title": "An uneven ratio of hardener to resin",
            "correct": false
        },
         {
            "title": "been cured in a well ventilated space that has a temperature of about 72 degrees",
            "correct": true
        }  
    ],
    "correctNotice": "That's correct",
    "incorrectNotice": "That's incorrect"
}

CLASS PROJECT

Share a photo of your finished project with the class!

Nice work! You've completed the class project