to mix into mortar and have no dirt in
it. The kinds of pitsand are these: black, gray, red, and carbuncular.
Of these the best will be found to be that which crackles when rubbed in
the hand, while that which has much dirt in it will not be sharp enough.
Again: throw some sand upon a white garment and then shake it out; if
the garment is not soiled and no dirt adheres to it, the sand is
suitable.

2. But if there are no sandpits from which it can be dug, then we must
sift it out from river beds or from gravel or even from the sea beach.
This kind, however, has these defects when used in masonry: it dries
slowly; the wall cannot be built up without interruption but from time
to time there must be pauses in the work; and such a wall cannot carry
vaultings. Furthermore, when sea-sand is used in walls and these are
coated with stucco, a salty efflorescence is given out which spoils the
surface.

3. But pitsand used in masonry dries quickly, the stucco coating is
permanent, and the walls can support vaultings. I am speaking of sand
fresh from the sandpits. For if it lies unused too long after being
taken out, it is disintegrated by exposure to sun, moon, or hoar frost,
and becomes earthy. So when mixed in masonry, it has no binding power on
the rubble, which consequently settles and down comes the load which the
walls can no longer support. Fresh pitsand, however, in spite of all its
excellence in concrete structures, is not equally useful in stucco, the
richness of which, when the lime and straw are mixed with such sand,
will cause it to crack as it dries on account of the great strength of
the mixture. But river sand, though useless in "signinum" on account of
its thinness, becomes perfectly solid in stucco when thoroughly worked
by means of polishing instruments.

CHAPTER V

LIME

1. Sand and its sources having been thus treated, next with regard to
lime we must be careful that it is burned from a stone which, whether
soft or hard, is in any case white. Lime made of close-grained stone of
the harder sort will be good in structural parts; lime of porous stone,
in stucco. After slaking it, mix your mortar, if using pitsand, in the
proportions of three parts of sand to one of lime; if using river or
sea-sand, mix two parts of sand with one of lime. These will be the
right proportions for the composition of the mixture. Further, in using
river or sea-sand, the addition of a third part composed of burnt brick,