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The vault's construction
Construction of any type of cross ribbed vault requires the making of a significant wooden structure: the centerings. When compared to the wooden structure of a Romanesque vault, those of a cross ribbed vault are certainly considerably simpler. Instead of building a complete surface in wood, this type only demands lineal centering under the arches. With the help of light auxiliary means the filling of the web can be done. There is no doubt that the fact that the centerings are simpler and more economical explains the success of this type of vaults.
Thus, the construction of the vault begins with an important wooden work with the purpose of creating a horizontal platform located at the upper level of the tas-de-charges. This plan is extremely important and should be marked in the drawing of the layouts since it will serve as a reference to situate all the elements integrating the vault at their correct height. On that work plan must the plan of the vault be designed with total exactness so as to know the right position of all the arches and, especially, to locate the central keystone that will be situated on a right wood foot at its correct height (Fig. 31). Next, are the tas-de-charges placed, even if in a real building work, these precede the construction of the wooden structure; after the tas-de-charges, some strong buttresses will guarantee the vault's stability once the centerings disappear (Fig. 32).
Then, we proceed to adjust the centering and the upper ashlars of the tas-de-charges in a way lets the protruding mould of the ribs fit in the double face of the arches' centerings (Fig. 33). The adjustment between the wooden structure, the coordination with the springing cluster and the central keystone is a delicate operation on which depends the correct construction of the vault, and, only once it is finished, can the voussoirs be placed in the arches. That is the moment when we discover the efficiency in the vault's design, its big central moulding starts to fit in the rail formed by the centerings so as to prevent the side movements and to guarantee its perfect placing in spite of the large numbers of parts necessary to form the arch (Fig. ...). The voussoirs of the formeret arches are also meant to facilitate its correct placing: the fat cylindrical lateral moulding adapts to the centering's edge and once again it leads the placing of the voussoirs (Figs. 22 y 23). [....]
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