Cladding Requires 10 Bricks (Sandstone, Rounded Stone, Slate, Marble, Stone) and 10 Mortar. Requires an activated trowel and right-clicking on a reinforced cave wall to start. You don't need the materials in your inventory to start the cladding, but will need them in your inventory to actually build it. To remove the clad, activate a crowbar and right-click the clad wall.
From Left to Right: Marble, Rounded Stone, and Sandstone Cladding.
this is the only picture I have, I removed these clad walls after I took the pic.