The key to drying pottery clay without cracks is to dry it slowly and evenly. Mug handles are notorious for cracking at the joint because drying handles evenly can be tricky. So, what do you do if your mug handle has cracked at the joint? Here are some simple ways to fix handles that crack on mugs as clay dries.
Why do Handles Crack on Mugs as Clay Dries?
Before going over the fixes, let’s have a quick look at why handles crack on the joints of mugs.
Cracks happen because handles are usually made of thinner pieces of clay. Also, they are attached to the side of the pot, so there is more air circulating around them. For both these reasons, they tend to dry out more quickly.
If there is a difference in moisture content between the mug and the handle, cracks can occur. Sometimes these differences arise as the pot dries. Particularly if care isn’t taken the prevent the handle from drying out more quickly.
But sometimes, potters will wait a few days before attaching a handle. So, the handle itself has more moisture than the mug. If the pot has dried out too much, it’s harder to get the handle to a matching moisture level.
It is not so important whether the handle is more or less wet than the mug when it’s attached. What is more important is that there is a differential in moisture content right from the start.
This sets up a drying gradient, which is hard to even out and gets worse during the drying process. If the body of the mug has more moisture than the handle, it will shrink at a different rate.
This causes internal tension, which can lead to handles that crack on mugs as the clay dries. Handles crack at joints as they dry because the joint is the weakest part of the structure.
So, the question is, what can you do if you have handles that crack on mugs as clay dries? Can you fix this situation? What can be done? And what is the best fix?
How to Fix Handles That Crack on Mugs as Clay Dries.
Here are 8 ways to fix your cracked mug handle joints. Some work better for moist clay, others work best on dry clay.
Fix 1: Vinegar / Vinegar Slurry
Take a small amount of bone dry clay. The amount of clay you need will depend on the size of the crack. But normally something the size of a small tomato is enough.
Use the same clay body that you have used to make your mugs. Crush the dried clay up in a container. A mortar and pestle works well to crush the clay. But if you don’t have a mortar and pestle, the back of a spoon and a bowl will work fine.
Crush the clay up into a powder. A few small chunks are fine, just as long as it’s small crumbs rather than big hunks of clay.
Pour a small amount of ordinary clear vinegar onto the crushed clay. I use a tablespoon to add the vinegar gradually. Don’t add too much vinegar, as you are going to be making a thick paste, rather than a thin slip.
If you make a mix that is a bit runny, just add more powdery clay to thicken it up. It needs to be the consistency of paste, like peanut butter, rather than liquid slip.
Vinegar is a flocculant, which means that it causes the clay particles to attract one another. It is often used to thicken clay slurries. (source).
How to Apply the Vinegar Slurry
Before applying the paste to the cracked joint, dab some vinegar on the joint with a sponge. Don’t make the clay near the crack too wet. You just need to dampen it. If you make it too wet, you just set up another drying gradient.
Once you have dabbed vinegar on, apply a little of the vinegar slurry/paste to the crack. Gently work the paste into the crack with whatever modeling tool you like. A wooden tool is fine.
You can fill the crack a little like you would use plaster to fill a crack in the wall. Once you have worked the clay paste in, smooth the surface over.
In all likelihood, the crack will re-open a little as it dries. You simply need to repeat the process again refilling the crack. Each time it opens, the crack will be a little smaller until eventually, it stays closed. You may have to repeat the filling process 3 or 4 times.
Fix 2: Magic Water
Vinegar paste or slurry is good if your clay is relatively dry. But if your clay is still a little wet, and workable, magic water can be a good fix for cracks.
What You Will Need for Magic Water:
- 1 gallon of water
- 3 tablespoons of liquid sodium silicate (9.5 grams)
- 1 ½ teaspoon of soda ash (3 grams)
This recipe is often credited to the ceramicist Lana Wilson. Simply apply the magic water to one side of the cracked join. There is no need to score the surfaces. Simply press the surfaces together, giving them a gentle, firm press and wiggle.
If the clay is a little plastic, there is enough give in the clay to move and wiggle the handle.
Soda ash and sodium silicate are both deflocculants. So, in contrast to vinegar, magic water is a deflocculant. This means that it causes the clay particles to repel each other. The magic water causes the clay particles to separate so that they can move about and mingle with each other.
Sodium silicate contains silica, which is a glass former. When it is wet, it is sticky. And when it dries, it is hard. So, the magic water creates a sticky surface when it wets the clay. And a hard bond when the clay and magic water dry together (source).
Fix 3: Paper Clay Slip / Magic Mud
Paper clay slip is also known as Magic Mud. This can be used to join handles that crack on mugs as clay dries.
It can also be used as a slip to attach handles in the first instance. It creates a strong bond and can help prevent the joint from separating in the first instance.
This mixture is credited to the ceramicist Martha Grover.
What You Will Need for Paper Clay:
- Some squares of toilet paper
- White vinegar
- A stick blender
- A mixing bowl
- Crushed bone dry clay
Tear up a few sheets of toilet paper and put it in a mixing bowl. Add the vinegar and whiz it together into a pulpy mix with the stick blender.
Add some crushed bone dry clay to the mix and stir it together until you get a thick paste. Remember to use the same clay as you used for your mugs. You have to be careful about mixing different clay bodies.
Cover the mix in a plastic bag and let the paste sit for a few hours.
Then, slip and score the ends of the handle that have come away from your mug. Also, slip and score the surface of the mug where you want the handle to attach.
If only one end of the handle has cracked, you may need to slice the other end too. This will allow you to remove the handle completely and slip and score it thoroughly. Then reattach the whole thing.
Alternatively, you can soften the handle and mug again. This will make the handle more flexible again. Once flexible, you may be able to move the cracked end away from the mug enough to slip and score. That way, you could avoid having to take the handle off completely.
One way to soften your greenware after it has become leather hard is to use a damp box. Read on to find out a little more about what a damp box is and how to use them….
Fix 4: A Damp Box
Another way to approach fixing handles that crack on mugs as clay dries is to rehydrate your greenware. One of the best ways of rehydrating pots and mugs evenly is by using a damp box.
A damp box is any sealed container that traps moisture in the atmosphere to keep the air humid.
You can make a simple damp box very easily. Briefly, you can pour a couple of inches of wet plaster mix into a plastic storage box. When the plaster has set, you keep it moist by adding water. Place your greenware on the plaster and put a lid on the container.
There needs to be enough water on the plaster to make it moist. But not so much that the greenware is sitting in a puddle. The water in the plaster will keep the atmosphere in the container damp. And it will rehydrate dry clay over a period of days.
Once the cracked piece has been rehydrated, you can re-attach the handle using slip, magic water or paper clay.
Getting the handle and the body of the mug to a similar moisture level, it’s less likely to crack again.
You can watch the full step-by-step video on how to make a damp box for clay on YouTube.
If you don’t have a damp box, there are other ways you can rehydrate your mug to repair a handle. Here is one of them…
Fix 5: Wetting the Cup and Handle – Cloth/Paper Towel
Another way to rehydrate greenware is to wrap it in a moist cloth and cover it in a plastic bag. It’s best if the cloth is lightweight and untextured. This reduces the chance of getting an impression of the fabric on your work.
Other potters wrap their work in damp paper towels. If you do this you need to make sure the towels don’t dry out. If they dry out they can actually dry your mug out even more.
Once the clay is workable again and has an even moisture level, you can slip and score the cracked handle. And then reattach it to the body of the mug.
Fix 6: Spooze
Whilst magic water is good if your clay is still a little wet, Spooze works if your clay is dry.
Like paper clay, Spooze has a thick paste-like slurry consistency. It was originally the idea of a ceramicist called Peggy Heer. It has a remarkable reputation for creating strong bonds between cracks in dry clay. And can be used to build up a thick layer to fill wider gaps, rather than just mending hairline breaks.
What You Will Need for Spooze:
- 1/3 white vinegar
- 1/3 cheap syrup (Karo syrup or any kind of corn syrup is fine)
- 1/3 dried and ground-up clay
- A little peroxide
The powdered, ground-up clay needs to be the same as the clay body you used on your mug. Mix the dried clay with the vinegar and syrup to make a thick paste.
Some recommend that you add a few drops of peroxide. The peroxide stops mold from growing and means you can keep any unused mixture. However, it’s so easy and cheap to make, keeping unused Spooze seems like a waste of shelf space to me.
To use the Spooze mixture, spray the two surfaces that you want to join with vinegar to moisten them. Then paste a bit of the Spooze onto either surface and press them together. Hold for half a minute and then let the join dry.
After the joint has dried you may need to sand off any Spooze that has squelched out of the join.
If you have a large crack, Spooze can also be used to build up layers. Simply spritz the surface of the crack, spread on some Spooze, and let it dry. Then repeat the process until the gap is filled. It’s a bit like using Spackle to fill holes in your wall.
Once the build-up layers have filled the gap, you will need to sand down the surface to make it flush.
If you would rather not make your own paste for greenware repair, there are commercially made clay menders. Here are a few…
Fix 7: Mayco’s AC-306 Clay Mender
Mayco’s clay mender can be used on greenware or bisque, though Mayco does state that it’s best for greenware repairs.
To use AC-306 (a catchy name!) you simply apply a little to the two surfaces to be joined. Then score the moistened surfaces. Once you have scored the surface with a needle tool or similar, apply another generous layer of the clay mender.
Press the two surfaces together and hold them for about 10 or 20 seconds. Once the join has dried, you can sand away the excess that has squished out of the join.
You can also use Clay Mender for larger cracks and holes by adding some of the clay you are using. Crush up some dried clay and mix it into the Clay Mender, until you have got a spackle consistency. Then you can use the paste to build up layers, letting the layers dry between applications.
The Clay Mender can dry a slightly different color to the piece you have mended. Also, glaze will sometimes not stick to the mended area. You can fix both of these issues by concealing the patched area with underglaze before glazing.
Fix 8: APT II
APT II is an additive that thickens slip and clay. It can be used on greenware, bisque or glazed pieces.
To use APT II, you simply pour some slip into a container and add a small amount of APT II. As you mix the two together, the slip will start to thicken up.
If it gets too thick, you can just add a little more slip. Don’t thin it out with water, because adding water to the mix will make it shrink as it dries.
You can use this slip on wet or dry greenware. The mixture is applied directly to the two surfaces to be joined. You don’t need to score the surfaces, simply apply to both and press them together. The APT II slip will act as an immediate gluing agent.
It’s a good idea to wipe any excess off from the outside before it hardens. Wipe it off with a damp sponge, but make sure not to make the area too wet. Water makes the APT II mix shrink and will cause the crack to reopen.
How to Avoid Cracks in the First Place
Here are some future tips to help you avoid handles that crack on mugs as the clay dries:
- Don’t wait too long before you attach your handles. Let them sit to firm up a little, but attach them when the clay is still fresh and workable.
- Make sure that the mug and the handle are of the same moisture content before you attach the two.
- Dry your mugs upside down and cover them over so they dry slowly. Generally, handles that crack on mugs as clay dries, do so at the top join. This is because the top of the mug is drying out more quickly than the lower portion. Inverting your mug will slow the drying process.
- Clay has a memory and wants to return to its original shape as it dries. It’s a good idea to let your handles set in their curved shape before you attach them. Also, it can help to over-curve the handle a little bit before you let it set. This means that if the clay handle tries to straighten as it dries, it won’t pull at the joint.
- Wrap your handles in plastic to stop them from drying out too quickly.
- Another tip is to paint wax resist on the handle or handle join. If you use wax resist, leave a narrow strip along the handle that is not painted with the wax. This gives a small area where moisture can evaporate slowly.
- Attach the handles with paper clay (magic mud) going forward. This will make a strong join that is less likely to crack as the clay dries.
Sometimes you will be able to fix handles that crack on mugs when clay dries. Other times you won’t be able to salvage a piece.
You may find that your mug looks fine after the fix. Then when you bisque fire, the crack opens up again.
Whilst you can use a bisque fixer like bisque fix, I would be reluctant to do this on a mug. I wouldn’t be happy using a mug that I suspected was structurally weak. And I certainly wouldn’t be happy giving it or selling it to someone else.
Also, whilst you may love your mug and want to save it, your time is precious too. It can be arduous trying to fix handles that crack on mugs as clay dries. You need to decide if your time is best spent fixing this problem or chalking it up to experience. Sometimes, it is best to move on.