_Of the Walls._
[Sidenote: _Lib. 4. Chap. 2._]
The 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.
There are many Precautions to be given to make the Masonry more firm and
durable, and these Precautions are common to all the different sorts of
Masonry.
[Sidenote: _Lib. 1. Chap. 5._]
When you would have the Walls very thick, for great and heavy Buildings,
you must strengthen the inner part of the Wall with long Piles of singed
Olive, which serves for Keys and Braces, for this Wood being so prepar'd
never corrupts.
[Sidenote: _Lib. 6. Chap. 11._]
[Sidenote: _Vide Index._]
It is likewise of great Importance for the strength of Walls, that all
be directly Perpendicular, and that the _Chains_, the _Pillars_ and
_Pieds-droits_ or _Piers_ be so situated, that _solid_ always answer'd
to the _solid_; for if there be any part of the Wall or any Pillar that
carrys false, it is impossible the Work should continue long.
There are also two ways of strengthning the Walls, which are either to
ease them of their own weight, or of that of the Earth which they are to
support.
The first way of easing is in those Places where there are void spaces,
as above Doors or Windows. These easements may be made two different
ways; the first is to put over the Lintel which supports the Wall, which
is over the void space of the Gates and Windows, two Beams, which lying
or resting below directly upon _Pieds-droits_ or _Piers_ meet together
above.
The other way is, to make directly over the void spaces Vaulted Arches
with Stones cut corner-ways and tending to one Center. For the Walls be
so strengthned by the means of these easements, that part of the Wall
which is below will not sink at all being easied of the load of the part
that is above, and if some defect should happen by tract of time, it
may be mended without propping that which is above.
The second way of easing, is, for Walls that are made to support the
Earth; for, besides the extraordinary thickness which they ought to
have, they should have likewise Buttresses on that side next the Earth,
so far distant one from another as is the breadth of the Wall; they
ought likewise to have an _Emparement_ or large Foundation which must be
equal to the height of the Wall, so that they go diminishing by degrees
from the bottom to the top, where they come to equal the height of the
Wall.
[Sidenote: _Lib. 1. Chap. 5._]
The effect of these _Buttresses_ is not only to support the Earth by
their Resistance, but likewise to lessen its Efforts when it swells, in
dividing it into many parts.
[Sidenote: _Lib. 6. Chap. 11._]
And if it be judg'd that these _Buttresses_ be not sufficient, the Wall
also which supports the Earth must be strengthned with other
_Buttresses_ within.