build with soil, plaster over with soil
墐 centers on working with soil as a building material: constructing with earth or plastering surfaces with mud or clay.
墐 combines 土 (earth, soil) with 堇, which likely contributes the sound and may relate to clay or sticky soil. The exact historical development of 堇 is uncertain.
The left side is 土 (earth), and the right side 堇 looks like a mound of clay being shaped. Picture someone plastering a wall with sticky soil.
For キン, imagine a king (キン) ordering his workers to build with soil: king -> キン, and the earth is plastered onto the walls.