Wooden Curved Centering Arch Formwork and Fast-Setting Lime: Volto Erection

In the timber-rich regions of Northern Europe, erecting an arched stone vault was supported by vast forests of oak, pine, and fir. Carpenters could easily construct full-scale timber falsework (centering) that spanned entire cathedral naves, leaving the temporary scaffolding in place for months until the entire building was completed. In the arid Cyclades, however, timber was a precious luxury imported by ship from Mount Athos, Peloponnese, or the Black Sea.

A typical Cycladic village possessed only a few dozen structural timber poles, carefully hoarded and passed down through generations of builders. To construct vaulted homes, storehouses, and churches under these conditions of extreme resource scarcity, Greek island master masons developed a method of modular, mobile construction that extracted maximum structural efficiency from minimal timber resources.

The temporary wooden arch formwork is known in Cycladic carpentry as the kaloupi (from the Turkish kalıp, meaning mold) or armatura. Rather than constructing a solid wooden dome, the master carpenter built three or four identical curved timber ribs spaced 50 to 80 centimeters apart. Because long curved timbers were unavailable, each rib was assembled from short, segmented planks of wild cypress or pine, laminated together with staggered overlapping joints and pinned with wooden dowels or forged iron nails.

Across the top curved edges of these ribs, the carpenter nailed thin, flexible wooden laths (sandani) spaced approximately 10 to 15 millimeters apart. The resulting wooden cradle had a width of only 1.2 to 1.8 meters—just wide enough for two masons to work comfortably side by side. The entire apparatus was supported on vertical timber shores (stili), resting upon heavy timber mudsills laid along the room floor.

The critical mechanical component of the centering system was the pair of opposing hardwood folding wedges, known as sfines. Placed directly between the bottom of each vertical shore and the floor mudsill, these two matching triangular oak wedges were driven together until their combined height raised the centering deck to the exact springline elevation of the vault.

The genius of the folding wedge revealed itself during the striking process (to dekaloupoma). In traditional vaulting, removing falsework is the most dangerous moment of construction. If supports are knocked out violently, the sudden transfer of weight can shock the uncured masonry, causing immediate shear cracking and catastrophic collapse. By striking the thin ends of the folding wedges with wooden mallets, the carpenter drove them apart in tiny millimeter increments. The entire wooden centering settled downward smoothly and uniformly, allowing the volcanic stone vault to gently compress its mortar joints and assume its own self-supporting gravity arch with zero dynamic shock.

The velocity of this modular construction system was made possible by the unique chemistry of Santorini Theraic earth pozzolan mortar. Ordinary non-hydraulic lime mortar requires four to eight weeks of curing before centering can be safely struck. With Theraic earth, the hydraulic crystallization of calcium silicate hydrates develops significant load-bearing capacity within forty-eight to seventy-two hours.

This rapid strength gain allowed Cycladic builders to operate in continuous, rhythmic construction cycles. In a single working day, masons laid the volcanic scoria stones and drove the central keystone (klidi). Over the next two days, the mortar achieved its initial hydraulic set. On the fourth day, the wedges were struck, the centering was lowered, and the entire wooden rig was slid forward along timber skid rails to the next bay. In this manner, an entire ten-meter-long vaulted hall could be erected in less than three weeks using a single, reusable wooden formwork rig, demonstrating a triumph of frugal vernacular engineering.