The Ten Books on Architecture, 7.3

Vitruvius  translated by Morris Hicky Morgan

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Vaultings and Stucco Work

3When vaulting is required, the procedure should be as follows. Set up horizontal furring strips at intervals of not more than two feet apart, using preferably cypress, as fir is soon spoiled by decay and by age. Arrange these strips so as to form a curve, and make them fast to the joists of the floor above or to the roof, if it is there, by nailing them with many iron nails to ties fixed at intervals. These ties should be made of a kind of wood that neither decay nor time nor dampness can spoil, such as box, juniper, olive, oak, cypress, or any other similar wood except common oak; for this warps, and causes cracks in work in which it is used.

2Having arranged the furring strips, take cord made of Spanish broom, and tie Greek reeds, previously pounded flat, to them in the required contour. Immediately above the vaulting spread some mortar made of lime and sand, to check any drops that may fall from the joists or from the roof. If a supply of Greek reed is not to be had, gather slender marsh reeds, and make them up with silk cord into bundles all of the same thickness and adjusted to the proper length, provided that the bundles are not more than two feet long between any two knots. Then tie them with cord to the beams, as above described, and drive wooden pegs into them. Make all the other preparations as above described.

3Having thus set the vaultings in their places and interwoven them, apply the rendering coat to their lower surface; then lay on the sand mortar, and afterwards polish it off with the powdered marble. After the vaultings have been polished, set the impost mouldings directly beneath them. These obviously ought to be made extremely slender and delicate, for when they are large, their weight carries them down, and they cannot support themselves. Gypsum should by no means be used in their composition, but powdered marble should be laid on uniformly, lest gypsum, by setting too quickly should keep the work from drying uniformly. We must also beware of the ancients’ scheme for vaultings; for in their mouldings the soffits overhang very heavily, and are dangerous.

4Some mouldings are flat, others in relief. In rooms where there has to be a fire or a good many lights, they should be flat, so that they can be wiped off more easily. In summer apartments and in exedrae where there is no smoke nor soot to hurt them, they should be made in relief. It is always the case that stucco, in the pride of its dazzling white, gathers smoke not only from its own house but also from others.

5Having finished the mouldings, apply a very rough rendering coat to the walls, and afterwards, when the rendering coat gets pretty dry, spread upon it the layers of sand mortar, exactly adjusted in length to rule and line, in height to the plummet, and at the angles to the square. The stucco will thus present a faultless appearance for paintings. When it gets pretty dry, spread on a second coat and then a third. The better the foundation of sand mortar that is laid on, the stronger and more durable in its solidity will be the stucco.

6When not less than three coats of sand mortar, besides the rendering coat, have been laid on, then, we must make the mixture for the layers of powdered marble, the mortar being so tempered that when mixed it does not stick to the trowel, but the iron comes out freely and clean from the mortar trough. After this powdered marble has been spread on and gets dry, lay on a medium second coat. When that has been applied and well rubbed down, spread on a finer coat. The walls, being thus rendered solid by three coats of sand mortar and as many of marble, will not possibly be liable to cracks or to any other defect.

7And further, such walls, owing to the solid foundation given by thorough working with polishing instruments, and the smoothness of it, due to the hard and dazzling white marble, will bring out in brilliant splendour the colours which are laid on at the same time with the polishing.

These colours, when they are carefully laid on stucco still wet, do not fade but are permanent. This is because the lime, having had its moisture burned out in the kiln, becomes porous and loses its strength, and its dryness makes it take up anything that may come in contact with it. On mixing with the seeds or elements that come from other substances, it forms a solid mass with them and, no matter what the constituent parts may then be, it must, obviously, on becoming dry, possess the qualities which are peculiar to its own nature.

8Hence, stucco that is properly made does not get rough as time goes on, nor lose its colours when it is wiped off, unless they have been laid on with little care and after it is dry. So, when the stucco on walls is made as described above, it will have strength and brilliancy, and an excellence that will last to a great age. But when only one coat of sand mortar and one of fine marble have been spread on, its thin layer is easily cracked from want of strength, and from its lack of thickness it will not take on the brilliance, due to polishing, which it ought to have.

9Just as a silver mirror that is formed of a thin plate reflects indistinctly and with a feeble light, while one that is substantially made can take on a very high polish, and reflects a brilliant and distinct image when one looks therein, so it is with stucco. When the stuff of which it is formed is thin, it not only cracks but also soon fades; when, however, it has a solid foundation of sand mortar and of marble, thickly and compactly applied, it is not only brilliant after being subjected to repeated polishings, but also reflects from its surface a clear image of the beholder.

10The Greek stucco-workers not only employ these methods to make their works durable, but also construct a mortar trough, mix the lime and sand in it, bring on a gang of men, and beat the stuff with wooden beetles, and do not use it until it has been thus vigorously worked. Hence, some cut slabs out of old walls and use them as panels, and the stucco of such panels and “reflectors” has projecting bevelled edges all round it.

11But if stucco has to be made on “wattle and daub,” where there must be cracks at the uprights and cross-sticks, because they must take in moisture when they are daubed with the mud, and cause cracks in the stucco when they dry and shrink, the following method will prevent this from happening. After the whole wall has been smeared with the mud, nail rows of reeds to it by means of “fly-nails,” then spread on the mud a second time, and, if the first rows have been nailed with the shafts transverse, nail on a second set with the shafts vertical, and then, as above described, spread on the sand mortar, the marble, and the whole mass of stucco. Thus, the double series of reeds with their shafts crossing on the walls will prevent any chipping or cracking from taking place.

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