There are a variety of resources you can collect in No Rest for the Wicked that you can use to craft items or repair buildings in the game, including clay.
How to Grow Clay Without Giving the Bad Guys Rest
Clay is a relatively common resource that you can find during your travels as you fight through the war-torn areas of Isola Sacra. Unfortunately, you can’t just find it lying on the ground. Instead, you’ll have to do a bit of searching for the material, or you’ll have to open your wallet to one of the many vendors.
Here you will find Clay in No Rest for the Wicked.
Since clay is a common material in No Rest for the Wicked, there are a few places in the world where you can find the item. Unfortunately, you'll need a bit of luck to do so.