paste wall with dirt
槾 centers on applying a paste-like substance to a wall, specifically using dirt or mud as a coating material.
槾 combines 木 (wood/tree) with 曼, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with plastering or pasting walls with dirt, possibly involving a wooden tool.
The left side 木 suggests a wooden trowel or tool, and the right side 曼 looks like a spread-out covering. Picture using a wooden tool to spread mud paste smoothly over a wall.
For バン, imagine a wooden plank (バン) used to smooth the mud paste onto the wall: plank -> バン, and the wood 木 helps spread the dirt coating.