We have here to consider certain natural principles of construction,
and then the methods for the artificial preservation of the stone used
in buildings. Under the first head, there are four divisions.
_Selection of Stone._--As it is universally agreed that the utmost
importance rests upon the original selection of the building material,
it is here that all the resources of lithological science should be
called in. Only one investigation, aiming at thorough work, has ever
been carried through, that of the Royal Commission appointed for the
selection of stone for the Houses of Parliament. But the efforts of
these able men were restricted by the little progress made at that time
in the general study of rocks, and were afterward completely thwarted
by the discharge of the committee and by the delivery of the execution
of the work of selection to incompetent hands. There will be hereafter,
from investigations made in the light of modern researches, no excuse
for such annoying results and enormous expenses as those which attended
the endless repairs which have been required, since a period of four or
five years after the completion of the great building referred to.
_Seasoning._--The recommendations of Vitruvius 2,000 years ago have
been observed at times down to the day of Sir Christopher Wren, who
would not accept the stone which he proposed to use in the erection of
St. Paul's Cathedral, in London, until it had laid for three years,
seasoning upon the seashore. Since then little or no attention appears
to have been paid to this important requirement by modern architects,
in the heedless haste of the energy of the times. Building stone,
even for many notable edifices, is hurried from the quarries into its
position in masonry, long before the "quarry-sap" has been permitted,
by its evaporation to produce solid cementation in the interstices of
the stone.
_Position._--The danger of setting up any laminated material on edge,
rather than on its natural bedding-plane, has been widely acknowledged;
yet it is of the rarest occurrence, in New York city, to observe
any attention paid to this rule, except where, from the small size
or square form of the blocks of stone employed, it has been really
cheapest and most convenient to pile them up on their flat sides.
_Form of Projections._--The principle is maintained by all the best
English and French architects that projections (_i. e_., cornices,
sills, lintels, etc.) should be "throated," that is, undercut in such
a way as to throw off the dripping of rainwater, etc., from the front
of the building, but in New York this principle is almost universally
neglected. It was pointed out that the severity of our climate even
requires the further care that the upper surface of projections should
be so cut as to prevent the lodgment or long retention of deposits
either of rainwater or snow. It is immediately above and below such
deposits that the ashlar of our fronts is most rapidly corroded and
exfoliated, an effect evidently due mainly to the repeated thawing and
solution, freezing and disintegration, which are caused by the water,
slush, and snow, which rest, often for weeks, upon a window-sill,
balcony, cornice, etc. Thus from the initial and inexcusable
carelessness in the construction and form of the projections, and,
later, the neglect of the houseowner, due to ignorance of the
results involved, to remove the deposits of snow, etc., as fast as
they accumulate on the projections, is derived a large part of the
discoloration of the marble, Nova Scotia stone, or light colored
granyte, and especially the exfoliation of the brownstone beneath the
window-sills, balconies, etc., by the water alternately trickling down
the front and freezing, by day and by night, for long periods.
The artificial means of preservation are of two classes, organic
and inorganic. The former depend on the application of some organic
substance in a coating or in the injection of fatty matters; but, as
the substances are with greater or less rapidity oxidized, dissolved,
and carried away by the atmospheric fluids, the methods founded on
their use have been properly denounced by many authorities as only
costly palliatives, needing frequent repetition, and therefore exerting
an influence toward the destruction of delicate carving. The following
were discussed: coal-tar; paint, which has been used in New York for
many residences, as in Washington for the Capitol, and in London for
Buckingham Palace, etc., but lasts only a few years, and often even
permits the disintegration to progress beneath it; oil, often used
in New York, but as objectionable as paint; soap and alum-solution;
and paraffine, beeswax, resin, tallow, etc., dissolved in naphtha,
turpentine, camphene, oil, etc.
The preparations of an inorganic nature, which have been proposed and
used abroad, have in some cases met with success; but the exact nature
of their action, and the conditions to which they are each suited,
are yet to be investigated, especially with reference to the entirely
different climate by which the stone in our city is being tried. The
processes which have been proposed, and in some cases practically used,
involve the application of the following substances: waterglass, in
connection with salts of calcium or barium, or bitumen; oxalate of
aluminum; barium solution, in connection with calcium superphosphate
or ferro-silicic acid; copper salts, used by Dr. Robert in Paris to
stop the growth of vegetation on stone, etc. There is certainly a
call for processes by which, at least, those stones which are used
in isolated, exposed, and unnatural positions may receive artificial
protection, such as the stone sills and lintels of windows, stone
balusters, projecting cornices, and ashlar-stone set up on edge. It
will doubtless be found that only those stones which possess a coarse,
porous texture and strong absorptive power for liquids will be found
particularly available for protection by artificial preservatives, and
that such stones should indeed never be used in construction in a raw
or crude state. In the spongy brown and light olive free-stones, a
marble full of minute crevices, and a cellular fossiliferous limestone,
a petrifying liquid may permeate to some depth, close up the pores
by its deposits, and incase the stone in solid armor; while, upon a
more compact rock, such as a granyte or solid limestone, it can only
deposit a shelly crust or enamel, which time may soon peel off. The
carelessness with which stone is selected and used, and the ignorance
in regard to its proper preservation, when the decay of a poor stone
becomes apparent, have led to an increased use of brick and terra
cotta, much to be deplored; durable stones are to be obtained in great
variety, methods for the preservation of the porous stones can easily
be devised, and stones of a fireproof character do exist in this
country in abundance.
In conclusion, three suggestions were offered: 1st, that householders
invoke the magic use of the broom on the fronts of their residences as
carefully as upon the sidewalks; 2d, that house-builders insist upon
the undercutting of all projections, and the exclusion of brackets or
other supports to sills and cornices, which only lead to the oozing of
water and a line of corrosion down the ashlar; 3d, that house repairers
recut the projections in this way, whenever possible, and entirely
avoid the use of paint, oil, or other organic preservatives.
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