wall plaster; wall clay; wall mud
Refers to the earthen plaster or clay mixture used for traditional Japanese walls, often in wattle-and-daub construction.
古い家の壁土が剥がれ落ちている。
The wall plaster of the old house is peeling off.
Compound of 壁 (wall) and 土 (earth, soil). The reading つち for 土 is the native Japanese reading.