HE right ordering of Stones joined with Mortar, which is call'd Masonry, is sevenfold; there are three of them which are of hewed Stone; viz. that which is in Form of a Net, that which is in Binding, that which is call'd the Greek Masonry. There are likewise three sorts of Masonry of unhewed Stones; viz. that which is of an equal Course; and that which is of an unequal, and that which is fill'd up in the middle; the seventh is compounded of all the rest.
The Net-Masonry is that which is made of Stones perfectly squar'd in their Courses, and are laid so, that the Joints go obliquely, and the Diagonals are the one Perpendicular, and the other Level. This is the most pleasing Masonry to the Sight, but it is apt to crack. See the Figure A. [Table I.]
The Masonry call'd the Bound-Masonry, is that, as Vitruvius explains it, in which the Stones are plac'd one upon another like Tiles; that is to say, where the Joints of the Beds are Level, and the Mounters are Perpendicular; so that the Joint that mounts and separates two Stones falls directly upon the middle of the Stone which is below.
Some Authors call this sort of Masonry Incertain, but they are mistaken; for they read Incerta instead of Inserta; it is not so Beautiful as the Net-work, but it is more solid and durable. See the Figure BB. [Table I.]
The Masonry which Vitruvius says is particular to the Greeks, is that, where after we have laid two Stones, each of which make a Parement or Course, another is laid at the end, which makes two Parements or Courses, and all the Building through observe this Order. This may be call'd Double-Binding; for the Binding is not only of Stones of the same Course one with another, but likewise of one Course with another Course. See Figure CC. [Table I.]
The manner of Walling by unequal Courses call'd Isodomum by the Ancients, differs in nothing from the Masonry call'd Bound-Masonry, but only in this, that the Stones are not hewed. See Figure D. [Table I.]
The other manner by unequal Courses call'd Pseudisodomum is also made of unhewed Stone, and laid in Bound-Work, but they are not of the same thickness, and there is no equality observ'd, but only in the several Courses, the Courses themselves being unequal one to another. See Figure A. [Table I.]
The Masonry which is fill'd up in the middle, call'd by the Ancients Emplecton, is likewise made of unhewed Stone and by Courses, but the Stones are only set in order as to the Parements or Courses, but the middle is fill'd up with Stones thrown in carelesly among the Mortar. See Fig. FF, GG, H. [Table I.]
Among all these sorts of Masonry, that will always be best which is made of Stones of an indifferent size, rather lesser than greater; to the end that the Mortar penetrating them in more parts may bind them faster, and the strength of the Mortar does not so soon decay. For we see that the Mortar which is laid in the Joints or Seams of the greater Stones with time decays and turns to Dust, which never happens to the most Ancient Fabricks which have been built of little Stones. From thence we may conclude, that it is ill Husbandry to be sparing of Mortar.
For this reason Vitruvius proposes another sort of Masonry, which may be call'd the Compound Masonry, for it is all the former together, of Stones hewed and unhewed, and fastned together with Cramp-Irons. The Structure is as follows: The Courses being made of hew'd Stone, the middle place which was left void is fill'd up with Mortar and Pebbles thrown in together; after this they bind the Stones of one Parement or Course to those of another with Cramp-Irons fasten'd with melted Lead. This is done to the end, that the abundance of Mortar which is in the middle may furnish and communicate a sufficient Humidity to the Joints of the great Stones which make the Parements. See the Figure K. [Table I.]