There are difficulties connected with the floors on or near the
ground, by reason of the dry rot incident to such places. Dry rot
consists in the development of fungus growth from spores existing in
the wood, and waiting only the proper conditions for their
germination. The best condition for this germination is the exposure
to a slight degree of warmth and dampness. There have been many
methods of applying antiseptic processes for the preservation of wood;
but, irrespective of their varying degrees of merit, they have not
come into general use on account of their cost, odor, and solubility
in water.
It is necessary that wood should be freely exposed to circulation of
air, in order to preserve it under the ordinary conditions met with in
buildings. Whenever wood is sealed up in any way by paint or varnish,
unless absolutely seasoned, and in a condition not found in heavy
merchantable timber, dry rot is almost sure to ensue. Whitewash is
better.
There has recently been an instance of a very large building in New
York proving unsafe by reason of the dry rot generated in timbers
which have been completely sealed up by application of plaster of
Paris outside of the wire lath and plaster originally adopted as a
protection against fire. Wire lath and plaster is one of the best
methods of protecting timber against fire; and, if the outside is not
sealed by a plaster of stucco or some other impermeable substance, the
mortar will afford sufficient facilities for ventilation to prevent
the deposition of moisture, which will in turn generate dry rot.
Where beams pass into walls, ventilation should be assured by placing
a board each side of the beam while the walls are being built up, and
afterward withdrawing it. In the form of hollow walls referred to, it
is a common practice to run the end of the beam into the flue thus
formed, in order to secure ventilation.
I am well acquainted with a large mill property, one building of which
was erected a short time before the failure of the corporation, which
resulted in the whole plant remaining idle several years. After the
lapse of about five years this establishment was again put into
operation; but before the new mill could be safely filled with
machinery, it was necessary to remove all the beams which entered
walls and to substitute for them new ones, because the ends were so
thoroughly rotted that it would have been dangerous to impose any
further loads upon the floors. When floors are within a few feet of
the ground, unless the site be remarkably dry, it is essential to
provide for a circulation of air, which can be done very feasibly in a
textile mill by laying drain pipe through the upper part of the
underpinning, forming a number of holes leading into this space, and
then making a flue from this space to the picker room or any other
place requiring a large amount of air. The fans of the picker room,
drawing their supply from underneath the building, produce a
circulation of air which keeps the timber in good condition.
It is supposed by some that there is a difference in the quality of
timber according to the season in which it is felled, preference being
given to winter timber, on account of the greater amount of potash and
phosphoric acid which it is said to contain at that time. In some
parts of Europe it is a custom to specify that the lumber should have
been made from rafted timber, on account of the action of the water in
killing certain species of germs. Whatever may be the merits of either
of these two theories, the commercial lumber of the northern part of
this country is generally felled in winter and afterward rafted.
The action of lime in the preservation of wood has always been
attended with the most excellent results; although not suited to
places subject to the action of water, which dissolves the lime,
leaving the timber practically in its original condition. The
preservative action of lime upon wood is readily shown by the
admirable condition in which laths are always found. I doubt if any
one ever found a decayed lath in connection with plaster.
As an example of the action of lime as a preservative of lumber. I can
cite an instance of a mill in New Hampshire where the basement floor
was placed in 1856, the ledge in the cellar having been blasted out
for the purpose. The rock was very seamy, and abounded in water
issuing from springs or percolating from the canal supplying water to
the mill. The rock was blasted away to a grade two feet below the
floor, and most of the space filled up again by replacing the small
pieces of stone, so arranged as to form blind drains for the removal
of any water which might find its way under the floor.
Toward the top of this filling, finer stones were used, then about
three inches of gravel, which was covered with two inches of sand and
lime. Two years ago I was at this mill when some alterations requiring
the removal of the floor were in progress, and found that the lumber
was still in good, sound condition, except for a superficial decay on
the under side of the floor plank.
But there are frequent instances where it is necessary to place the
floor directly upon the earth, without any space or loose filling
underneath it, in order to save room, or to secure a firm support for
machinery. By way of information upon what has actually been
accomplished in this direction, I will cite instances of three floors
in such positions, all of which have to my knowledge fulfilled the
purpose for which they were designed.
The first instance is that of a basement floor laid twenty-one years
ago, a portion of which was made by excavating one foot below the
floor, six inches of coarse stone being filled in, then five inches of
coal tar concrete made up with coarse gravel, and finally about one
inch of fine gravel concrete. Before the concrete was laid, heavy
stakes were driven through the floor about three feet apart, to which
the floor timbers were nailed and leveled up. The concrete was then
filled in upon the floor timbers, and thoroughly tamped and rolled out
to the level of the top of the floor timbers. The under side of the
floor timbers was covered with hot coal tar.
This floor is still in good condition, and has not needed repairs
caused by the decay of the timber. Another portion of the floor laid
at the same time and in the same manner, with the exception that
cement concrete was used in the place of the coal tar, was entirely
rotted out in ten years.
Another floor was made in quite a similar manner. All soil and loam
was removed from the interior of the building; the whole surface was
brought up to the grade with a puddle of gravel and ashes; stakes two
and a half by four inches, and thirty inches in length, were driven
down; and nailing strips were secured to them. Over this puddled
surface a coat of concrete eight inches thick was laid, the top being
flush with the upper surface of the nailing strips. This concrete was
made of pebbles about two inches in diameter, well coated with coal
tar, and laid in place when hot. It was then packed together by being
tamped and rolled, and a thin covering of the tarred sand placed upon
the top, forming a smooth, hard surface. The first floor consisted of
two inches of matched spruce, grooved on both sides, and fitted with
hard pine splines, five-eighths by one and one-fourth inches. On the
top of this a hard pine 1¼ inch floor was laid over a course of
building paper.
Another method, which is certainly more novel than either of the
others, consists in supporting a floor upon a bed of resin. The
underlying earth was removed, and replaced with spent moulding sand,
leaving trenches for the floor timbers, which were placed upon bricks
laid without mortar. Melted resin was poured into the space alongside
and underneath the timbers. The floor planks were then laid upon the
timbers, the tops of which were about half an inch above the level of
the sand. Holes were bored into the floor plank about four feet apart,
and melted resin then poured into the holes, so as to interpose a
layer of resin underneath the floor plank and beams. Upon this floor a
top floor of hard wood was laid in the usual manner. This floor has
been used for a number of years to support a large quantity of heavy
machine tools, principally planers, without yielding or depreciation
due to decay, and has proved to be most satisfactory.
In some instances asphaltum or coal tar concrete floors are not
covered with wood, although it is much more agreeable for the help to
stand upon wooden floors. It should be remembered that all these
compounds are readily softened by means of oil, and they should be
protected from oil by a coat of paint when not covered with wood; the
preferable method being to first apply a priming containing very
little oil, or a coat of shellac, and follow with some paint mixed up
with boiled linseed oil.
(_To be continued._)
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