claycap
nounUK /ˈkleɪkæp/
US /ˈkleɪkæp/
A claycap is a hard layer of clay that sits on top of something and seals it like a lid.
The old well was closed with a claycap to keep dirty water out.
OTHER MEANINGS
2. A protective clay layer placed over buried waste to keep water from getting in.
Engineers spread a claycap over the landfill to stop rain from soaking the trash.
3. A natural crust of clay that forms over the top of a soil or rock layer.
Digging down, we hit a claycap that the roots could not get through.
4. A small cap or cover made of clay, as on an old pipe or jar.
The potter fitted a claycap on the jar before firing it.