Why Does Air Dry Clay Crack?

Quick Answer

Air dry clay usually cracks because different parts of the clay are drying and shrinking at different speeds. Very thick sections, thin edges, too much added water and drying the clay too quickly can all increase the chance of cracks. Keeping the thickness reasonably even and allowing the project to dry gradually can help prevent them.

1. Keep the Thickness as Even as Possible

Try to avoid having very thin areas immediately next to very thick ones. A reasonably consistent thickness helps the whole project dry at a more similar rate.

2. Don't Make the Clay Unnecessarily Thick

Very thick pieces take much longer to dry through to the centre. For larger projects, consider whether the shape can be made hollow or built around a suitable lightweight form rather than using a solid mass of clay.

3. Use Water Sparingly

A small amount of water can be useful for smoothing the surface or helping with joins, but avoid repeatedly soaking the clay. Use only as much as you need.

4. Join Pieces Carefully

Simply pressing one piece of clay onto another may not create a strong join. Lightly roughening the two surfaces before joining and blending the clay around the connection can help the pieces hold together as they dry.

5. Let the Clay Dry Gradually

Leave your project somewhere dry and well ventilated, away from direct heat and strong sunlight. Trying to speed up the process can cause the surface to dry before the inside has had time to lose its moisture.

6. Allow Air to Reach Different Sides

Flat pieces can dry faster on the exposed surface than underneath. Once the clay is firm enough to handle without damaging it, carefully turning the piece can help the underside continue drying.

7. Be Patient with Thick Pieces

A project can feel dry on the surface while still containing moisture inside. Larger and thicker pieces will naturally need more time than small, thin decorations.

Common Mistakes to Avoid

Don't try to dry air dry clay with strong heat. Rapid drying can make the outside shrink before the inside has dried.

Don't use lots of water to make the clay easier to work. Too much added moisture can make drying less even.

Don't make delicate areas too thin. Very thin edges dry quickly and are also more vulnerable to breaking.

Don't simply stick separate pieces together and hope they hold. Take time to prepare and blend joins, particularly on handles and raised decorations.

Don't assume the clay is completely dry because the surface feels dry. Thick projects can still contain moisture in the centre.

Can you fix cracks in air dry clay?

Small cracks can often be improved by working a small amount of fresh clay into the damaged area and smoothing the surface. The repair will then need to dry completely. Larger structural cracks may indicate that the piece has dried unevenly or that the surrounding clay is under tension, so a repair may not always prevent the crack from returning.

Why does air dry clay crack while drying?

The clay shrinks slightly as moisture evaporates. If one section dries and shrinks faster than another, the resulting tension can cause a crack. Uneven thickness and rapid drying are common reasons for this.

Can air dry clay dry too quickly?

Yes. Putting air dry clay next to a radiator, heater or in strong direct sunlight can cause the exposed surface to dry much faster than the inside. A slower, more even drying process is generally preferable.

How thick should air dry clay be?

There isn't one correct thickness for every project, but consistency is important. Avoid combining extremely thick areas with very thin sections where possible. Larger solid pieces will also take considerably longer to dry than thinner projects.

How long does air dry clay take to dry?

Drying time depends on the clay, thickness of the project, room temperature, humidity and airflow. Small, thin pieces can dry much faster than large sculptures. Always check the instructions supplied with your particular clay and allow extra time for thick sections.

Should I add water to air dry clay?

Small amounts of water can be useful for smoothing and joining, but it should be used sparingly. Adding too much water can make the clay sticky and increase the amount of moisture that eventually needs to evaporate.

Why is my air dry clay warping?

Warping often happens when one side of a flat piece dries and shrinks faster than the other. Once the piece is firm enough to move safely, turning it during the drying process can help expose both sides to the air.

Why do pieces keep falling off my air dry clay?

Attached pieces need a good mechanical join. Prepare the surfaces where possible, press them together securely and blend the clay around the connection. Heavy additions attached by only a very small area are particularly vulnerable.

Can I paint air dry clay?

Many air dry clays can be painted once completely dry, with acrylic paint commonly used for craft projects. Check the instructions for your particular clay before decorating, and make sure there is no remaining moisture trapped inside the piece.