Generally, no, you cannot reliably attach wet clay to air dry clay.
While an inexperienced beginner might be able to initially join wet clay to a nearly bone-dry piece of air dry clay, the differing shrinkage rates will almost always lead to cracking and separation. The wet clay shrinks significantly as it dries, while the air dry clay, already mostly dry, shrinks very little. This difference in shrinkage creates stress at the join, leading to failure.
Here's a breakdown of why it doesn't work and what happens:
- Differential Shrinkage: Wet clay contains a large amount of water. As it dries, this water evaporates, causing the clay to shrink considerably. Air-dry clay, having already lost most of its moisture, experiences minimal shrinkage.
- Stress at the Join: The shrinking wet clay pulls on the relatively stable air-dry clay. This creates tension at the point where they are joined.
- Cracking and Separation: The stress eventually exceeds the bond's strength, resulting in cracks appearing at the join, and ultimately, the two pieces separating.
Even with careful techniques like scoring and slipping (applying a clay slurry), the fundamental problem of differential shrinkage remains. These techniques work for joining wet clay to wet clay (or even leather-hard clay), but not wet to air dry.
To illustrate: Imagine trying to glue a wet sponge to a dry rock. As the sponge dries and shrinks, it will pull away from the rock because they shrink at drastically different rates. The same principle applies to wet clay and air dry clay.
Therefore, the safest approach is to work with clay that is at a similar moisture level throughout the project to minimize the risk of cracking and separation due to uneven drying.
