Alberti, Leone Battista, Architecture, 1755

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CHAP. IX.
In all Incruſtations there muſt be at leaſt
three
Coats of Mortar; the firſt is called
Rough-caſting
, and its Office is to ſtick as cloſe
as
poſſible to the Wall and to bind on the two
outer
Coats; the Office of the outer Coat, is
to
make the Work ſhew neat, ſmooth, and po­
liſhed
; that of the middle Coat, which we call
Plaiſtering
, is to prevent any Faults or Defects
in
either of the other two.
The Defects are
theſe
: If the two laſt, that is to ſay, the Plaiſt­
ering
and the outer Coat are ſharp, and to uſe
ſuch
an Expreſſion, tenacious of the Wall, as
the
Rough-caſt ought to be, their Acrimony
will
occaſion an infinite Number of Cracks in
them
in drying.
And if the Rough-caſt be
ſoft
, as the outer Coat ſhould be, it will not
take
hold of the Wall as it ought, but will fall
off
in Pieces.
The oftener we plaiſter the Wall
over
, the better we may poliſh it, and the
longer
it will endure the Injuries of Time.
Among the ancient Buildings I have ſeen ſome
which
have been done over no leſs than nine
Times
.
The firſt of theſe ſhould be very ſharp,
and
made of Pit-Sand and Brick beaten not
too
fine, but about the Size of ſmall Gravel,
and
laid on about the Thickneſs of three
Inches
.
For the Plaiſtering, or middle Coat,
River-Sand
is better, and is leſs apt to crack.
This Coat too ſhould be ſomewhat rough, be­
cauſe
to a ſmooth Surface nothing will ſtick
that
you lay on.
The laſt of all ſhould be as
white
as Marble; for which Reaſon, inſtead of
Sand
you ſhould uſe the whiteſt Stone that can
be
got pounded ſmall; and it will be ſufficient
if
this Coat be laid on about half an Inch thick,
ſor
when it is much more, it will not eaſily
dry
.
I know ſome that, out of good Huſ­
bandry
, make it no thicker than a Piece of
Shoe-leather
.
The ſecond Coat, or Plaiſter­
ing
, ought to be ordered according to its Proxi­
mity
to either of the other two.
In Moun­
tains
where there are Stone-pits, you meet
with
certain Veins extremely like a tranſparent
Alabaſter
, which are neither Marble nor Tarres,
but
of a Kind of middle Nature between both,
and
very friable.
If this be beat ſmall and
mixed
up inſtead of Sand, it will ſhew full of
little
Sparks that will ſhine like a fine Sort of
Marble
.
In many Places we ſee Nails ſtuck
into
the Wall to keep on the Plaiſtering, and
Time
has proved to us that it is better to have
them
of Braſs than of Iron.
I am very much
pleaſed
with thoſe who, inſtead of Nails, ſtick
little
Pieces of Flint in between the Joints of
the
Stone; which they drive in gently with a
wooden
Hammer.
The freſher and rougher
the
Wall itſelf is, the faſter all your plaiſtering
Work
will cleave to it: For which Reaſon, if,
as
you build the Wall, and while the Work is
Green
, you rough-caſt it, though but ſlightly,
the
Plaiſtering and outer Coat will ſtick to it
ſo
faſt, as hardly ever to peel off.
After ſouther­
ly
Winds, it is very proper to do any of this
Sort
of Work; but if when a north Wind
blows
, or in any great Cold or Heat, you offer
at
any Sort of Plaiſtering, eſpecially at laying
on
the outer Coat, it will ſcale off preſently.
Laſtly, all Incruſtations are of two Sorts; either

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