Paras Volcanic Stone and Terracotta Sunken Pedestal Carving: Bale Bengong Plinth Masonry

The architecture of Bali is an organic child of its violent volcanic geology. The island is punctuated by active strato-volcanoes—Mount Agung, Mount Batur, and Mount Bratan—that have blanketed the landscape across millennia with deep deposits of pyroclastic ash, volcanic bombs, and volcanic pumice. In deep river canyons such as the Ayung and Oos valleys, this compacted ash sintered over geological time into batu paras—a soft, fine-grained volcanic tuff.

For Balinese stone sculptors (sangging), batu paras is the supreme medium. When freshly extracted from riverbank quarries, it is saturated with natural quarry water and can be pared, drilled, and sculpted using simple forged iron chisels and wooden mallets as easily as dry soap. As atmospheric carbon dioxide reacts with the porous silicates, the stone case-hardens, developing a tough exterior skin. Combined with vibrant, clamp-fired red clay bricks (bata merah), this volcanic stone forms the warm, earthy polychromatic masonry that serves as the architectural foundation of the Bale Bengong.

In the spatial cosmology of Balinese Hinduism, the base of any building belongs to the nista realm—the sphere of the earth, the underworld (bhurloka), and chthonic nature spirits. A pavilion plinth is never treated as a mere concrete footing; it is an active sacred cosmogram engineered to ground cosmic and subterranean energies.

Carved into the stepped lower terrace of the plinth is the colossal form of Bedawang Nala—the cosmic world turtle who carries the weight of the physical earth upon his back. Entwined around the turtle are two giant sacred serpents: Naga Anantaboga, the guardian of the soil and agriculture, and Naga Basuki, the spirit of water and prosperity. Together, these three mythological entities represent the immutable foundations of physical existence. By chiseling their protective likenesses into the batu paras stone, the master mason creates an architectural lightning rod designed to calm subterranean seismic tremors and anchor the light wooden pavilion above.

One of the most refined technical achievements of Balinese masonry is the kosok brick-laying technique. When constructing the inner structural core of the Bale Bengong plinth, masons do not apply thick, sloppy beds of mortar. Instead, they use clamp-fired red terracotta bricks that have been soaked in water to saturation point.

The mason places two wet bricks face-to-face with a thin sprinkle of fine brick dust and water between them. He then rubs the upper brick back and forth vigorously against the lower brick (ngosok). The frictional abrasion grinds down microscopic surface irregularities, creating a slurry of liquefied clay that fills all micro-pores. Under vacuum and contact pressure, the two bricks fuse together with an impenetrable bond, leaving a hairline joint under 0.5 millimeters thick. This zero-mortar jointing prevents tropical rainwater from penetrating the interior core, eliminating weed growth and preventing structural spalling across decades of intense tropical weather.

At the four corners of the upper plinth platform stand the most critical structural masonry components of the Bale Bengong: the umpak. Unlike the surrounding soft batu paras stone, umpak pedestals are chiseled from monolithic blocks of dense, unyielding volcanic andesite (batu candi)—the same durable black basalt stone used to construct ancient Javanese candi temples like Borobudur and Prambanan.

The umpak is sculpted in the form of a sacred blooming lotus flower (padma), featuring a wide square base that tapers gracefully to a circular, slightly domed top pad. Sited with absolute level precision at the four grid coordinates, the umpak serves two vital engineering functions. First, it elevates the wooden columns of the pavilion 200 to 300 mm above the floor plane, isolating the end-grain of the timber from standing mop water, seasonal splashing, and wood-destroying subterranean termites. Second, because the wooden columns rest freely atop the rounded stone surface without rigid steel anchor bolts, the umpak functions as a friction pendulum seismic bearing. During high-magnitude earthquakes, the entire timber pavilion can rock and slide micro-millimeters across the smooth andesite pads, dissipating seismic kinetic energy and preventing the building from collapsing.