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This is particularly so if the planks are a trifle higher than the concrete, as is likely to be the case when newly laid down. Then, too, where such a floor is of wood it is necessary to excavate a foot or so below the floor timbers, to provide an air space for preventing the decay of the materials.

To lay a concrete floor for this purpose the earth should be excavated to the depth of from 18 to 24 inches, according to the weights which the floor

is to carry.

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For ordinary purposes of machine shop work 22 inches is desirable and sufficient. If the ground is sufficiently firm at this level, no further preparation need be made. If soft and yielding, the excavation should be carried down to solid ground, and then filled up with solid earth, or still better with gravel, the excavation being flooded with water and the filling material thoroughly puddled as it is put in.

On top of this bed should be placed a layer of coarsely broken stone, from 8 to 12 inches deep; and upon this a layer of crushed stones, none of which should exceed 2 inches in dimension. This layer should be from 4 inches thick. On this is spread a layer 2 to 4 inches thick of concrete composed of one part Portland cement, two parts clean, sharp sand, two parts clean gravel, and three parts fine crushed stone — all taken by measure, and not by weight.

These ingredients should be mixed rather wet so as to settle well down into the spaces between the stones of the previous course. The concrete should be rammed hard and made perfectly level.

Then comes a coating of from 1 to 1 inch thick, consisting of a mixture of one part Portland cement and two parts clean, sharp sand, which should be laid before the former course is dry, in order that the two courses may firmly unite. This last course is laid quite wet, to facilitate “floating”

that is, the leveling off and smoothing.

Sometimes the intermediate course of concrete work is made up of shingle (coarse gravel, stones, or pebbles), mixed with hot coal tar or Portland cement; but this has the objection that, whatever be the medium used for cementing the mass, it will not adhere to the rounded surfaces of the pebbles as effectively as it does to the more porous surfaces of crushed stone.

Therefore, where subjected to hard usage, this shingle is more likely to disintegrate and break up than where crushed stone is used.

The gallery floors of the machine shop are supported on built-up girders 20 inches deep, placed at each of the columns dividing the wings from the central part of the building. Carried upon angle bars, riveted to the girders at a proper height, are the ends of 3 x 16-inch floor joists, placed 20 inches from center to center, their upper edges coming 2} inches above the top of the girders, which space is occupied by a spiking piece. On these joists is

laid a floor of 2} x 6 inch planks, planed on both sides and matched with tongue and groove.

This construction is shown in vertical section in Fig. 52. The girders here shown may, of course, be solid I-beams, with angle bars riveted on them for supporting the ends of the joists.

Where a lighter construction may be safely resorted to, on account of less weight to sustain, the form shown in Fig. 44 is proper. In this case an I-beam is used, say 10 to 15 inches deep, and the ends of the joists rest upon the lower flange of the beam. They should be of such depth as to project a couple of inches above the top of the beam, as shown, to provide a space for a spiking piece.

In either case the ends of the joists should be beveled as shown, so that they may drop out clear in case of fire, without displacing or warping the I-beams.

Wood joists may be dispensed with altogether, if safety from fire is of more consideration than first cost.

In this case I-beams of proper strength are laid upon the girders, or with their ends resting upon the lower flanges thereof — say 4 to 8 feet from center to center — and upon them are laid planed and matched floor planks from 3 x 6 inches to 5 x 8 inches, according to the distance between supports and the load to be sustained. These are bolted to the upper flange of the I-beam. This arrangement is shown in Fig. 52.

THE REMAKE

Fig. 52. — Floor Supported Entirely by Steel Beams. The vertical space occupied by these methods of construction varies considerably, as is shown in the engravings, and must be taken into account in designing the building.

Where it is desired to support floors by wooden beams, the form shown in Fig. 46 is proper. The dimensions of the beams must be sufficient to carry the load, taking into consideration also the distance between supports. The ends of the beams resting in the brick wall should be upon a “header course" of bricks, as shown, and the ends of the beam beveled off the same as if used in connection with an iron girder or I-beam, so that in case of fire the beam will fall freely out of the wall without injuring it.

Floor joists are laid upon the beams in the usual manner and spiked to them. Wooden floor joists should be braced by a “bridging” of say 2 x 3

inch scantling, as shown, placed at intervals of from 6 to 8 feet, according to the dimensions of the joists and the weights they have to support.

In using floor planks of 3 inches or over in thickness it will be found more economical to groove both edges of the planks and insert a separate piece as a tongue, than to cut a groove in one edge and a tongue in the other.

The selection of proper lumber for floors has already been referred to. It is often profitable to consider those things that have failed since it has been well said that “we learn as much by one failure as by two successes.” And the failures in shop floors are prolific sources of much annoyance and expense.

A certain machine shop floor was laid upon round chestnut timbers, flattened on top and bedded in gravel laid over "made land,” that is, loosely filled in with refuse matter of any sort easy to obtain.

The floor proper was of 2-inch spruce planks.

The result was that within a year the chestnut timbers and the under side of the planks began to decay, and since that time about one half of the timbers and nearly all the floor planks have been replaced each year, the patching-up process going on at intervals, and the constant result being an unsightly as well as expensive and annoying affair.

Within a hundred feet of this floor was another of 2-inch planks laid on 3 x 12 inch joists, supported on 12 x 12 inch timbers resting on piers, raising the floor about two feet above the ground.

Twelve years after this was laid some planks were removed to put in a machine foundation, and the joists and timbers were found looking nearly as fresh and new as when they came from the lumber yard.

Their elevation above the ground and the ventilation of this space by small gratings in the side walls were evidently the cause of their preservation. These cast iron gratings, say 10 x 18 inches, should be inserted at least every fifty feet in the walls of buildings whose ground floors are of wood, and at least a foot of ventilating space should be left between the ground and the floor.

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Another example, equally instructive, was a second floor of a machine shop. It was of 2} x 6 inch spruce planks, properly supported. They were grooved on each edge 4-inch wide and strips were inserted as shown in Fig. 53.

The builders evidently thought that planks 21 x 6 inches, with inserted tongues, would make a good and substantial floor. And so they would have,

but the unfortunate selection of the planks included many with the grain running in the wrong direction, which caused much warping and distortion.

Fig. 54 is from a sketch taken at the head of a stairway, careful attention having been given to the direction of the grain and the distorted form of the planks. It is, perhaps, needless to say that the tongues were split, and in some cases the planks also.

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Formerly the timbers most used in ordinary construction were of spruce. While this wood is well adapted for floor planks, it has very serious objections when used as supporting timbers. There is great liability to warp, twist, and crack as the seasoning process goes on, while its strength is not as great as some other easily obtained woods.

For instance, hard pine is superior in this respect, while it is about 35 per cent stronger than spruce, and its usual cost is only about 20 per cent greater.

The foundry floor is subjected to a very considerable weight, both in molding sand and in the castings produced, but the rough usage and shocks which the machine shop floor is called upon to withstand are not met with here. Consequently there is no need of such an expensive preparation.

The ground is prepared in the same manner as for the machine shop floor, except that it is only 12 inches below the floor line. This space is first covered with a 4-inch layer of crushed stone, over which is poured a thin mixture of one part Portland cement and two parts sand, mixed rather wet.

Then a concrete is made of the same mixture and finely crushed stone, and laid to a depth of about 3 inches. On top of this is spread a flowing coat of the cement and sand mixture from to -inch thick, which is properly leveled off. All this having thoroughly sct, the remaining portion of about 4 inches is made up of molding sand.

Pits are dug in the central portion of the foundry floor, of such number, area, and depth as the contemplated work renders necessary. The bottom is covered with 6 inches of concrete and laid with two courses of hard bricks. The side walls of the pits are 8 inches thick and are built of hard bricks, all laid in cement mortar.

The top of the wall is level with the final cement coat of the floor. It castings of ten tons or over in weight and with comparatively small bases are to be made in one of these pits it will be necessary to put down a more substantial bottom.

Excavation should be made to solid ground, or “hard pan,” and large stones laid in cement mortar built to within about a foot of what is to be the

bottom of the pit. Then proceed as above for making ready for the side walls. Care should be exercised in ramming or puddling, or both, to completely fill in around the side walls.

The floor of the forge shop is a still more simple matter than that of the foundry. The ground is prepared as before, and leveled off a foot below where the top of the floor is to be. This space is filled in with clean gravel mixed with clay, in the proportion of three parts of the former to one of the latter, laid down wet and thoroughly rammed down with a broad-faced rammer.

Sharp sand, or the fine cinders from forges, are sifted over this to prevent the surface from becoming muddy when accidentally wet. In the case of a forge shop, concrete is hardly advisable, being liable to be broken up by the heavy shocks from hammers and the rough usage to which it would be subjected.

Of course it might be made thick enough to endure these conditions, but would be quite expensive and would answer the purpose no better than a hard-rammed floor of earth, as above described.

For the floor of the boiler room, flag-stones or hard-burned bricks may be used, whichever is found most convenient. If stones are used they should be cut to a certain width, in one direction at least, in order that they may be laid in courses so as to break joints," as shown in Fig. 42. They should be from 1 to 2 inches thick.

Supposing the ground to be sufficiently solid for the purpose, it is prepared by leveling, the same as heretofore described, and at least 4 inches plus the thickness of the stones below where the top of the floor is to be. Sharp sand should be filled in 4 inches deep, and the stones laid upon this, the sand being rammed closely under each course as laid.

When completed, dry sand to the depth of 1 inch is spread over the whole and swept back and forth to force as much as possible down through the joints. This is the cheaper and more simple method.

If it is desired to make a more substantial pavement, the carth should be leveled off at such a height that only an inch space is left between it and the stones, and an inch course of a mixture of one part Portland cement and two parts of sharp sand worked up rather soft.

The stones are laid on this while it is wet, and all spaces filled as each course is laid and leveled. Some masons may prefer to make this mixture with a portion of lime added, the same as in cement mortar.

Should bricks be used they may be laid on either the sand or cement bed the same as described for stone, except that about half the depth of sand will be sufficient. They should be arranged in the form shown in Fig. 43, by which method they are firmly bound together, and, if laid only upon sand,

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