Scientific American Supplement, No. 647, May 26, 1888

by Various

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.