Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/503

PRECAUTIONS AGAINST FIRE.] so long as there is no access of air from below. But the Eng lish indoor plastering upon laths is commonly of the most fragile kind, and the slightest weight falling upon the back of a ceiling will make a breach through it, whilst the floors are commonly of deal laid upon fir joists, and are exposed to the action of fire from below directly the lathed and plas tered ceiling has failed ; if, indeed, the fire have not found its way to the joists under the flooring boards by the hollow lathed and plastered quartering partitions. In the timber enclosures and partitions, which economy induces the Paris builder to introduce as substitutes for walls, the timber is so embedded in and made part of a solid concrete, as to be protected from almost every casualty of which it is suscep tible. But the French render their floors also so nearly in combustible as to leave but little to desire in that respect, and in a manner attainable with single joists, as well, at the least, as with joists framed into girders. According to their practice, the ceiling must be formed before the upper surface or floor is laid, as the ceiling is formed from above instead of from below. The carpenters work being com plete, strong batten-laths are nailed up to the under sides of the joists, as laths are in England ; but they are much thicker and wider than our laths, and are placed so far apart that not more, perhaps, than one-half of the space is occupied by the laths. The laths being affixed and they must be coundly nailed, as they have a heavy weight to carry a platform, made of rough boards, is strutted up from below parallel to the plane formed by the laths, and at about an inch below them. Mortar is then laid in from above over the platform and between and over the laths, to a thickness of from 2 inches to 3 inches, and is forced in under the laths, and under the joists and girders. The mortar, being gauged, as plasterers term it, or rather, in great part composed of plaster of Paris, soon sets sufficiently to allow the platform to be removed onwards to another compartment, until the whole ceiling is formed. The plaster ceiling thus produced is, in fact, a strong slab or table, in the body of which the batten-laths which hold it up are incorporated, and in the back of which the joists, from which the mass is suspended, are embedded. The finishing coat of plastering is then laid on. Such a ceiling will resist any fire that can act upon it from below, under ordinary circumstances ; and it would be difficult for fire to take such a hold from above as to destroy the joists to which a ceiling so composed is attached, the laths and the under side of the joists being alike out of its reach ; and consequently such a ceiling alone would diminish the danger from fire, although the floor above the joists were laid with deal boards. ing A boarded floor, however, in Paris is a luxury not to be rials, found in the dwellings of the labouring classes, nor, indeed, are boarded floors to be found in any dwelling- houses but those of the more costly description. Whether the proposed surface is to be boarded or not, how ever, the flooring joists are covered by a table of plaster above, as completely as they are covered by a plaster ceiling below. Rough battens, generally split and in short lengths stout enough to bear the weight of a man without bending, are laid with ends abutting upon every joist, and as close together as they will lie without having been shot or planed on their edges. Upon this rough loose floor, mortar of nearly similar consistence to that used for the ceilings is spread to a thickness of about three inches ; and as it is made to fill in the voids at the ends and sides of the floor-laths upon the joists, the laths become bedded if! upon the joists, whilst they are to some extent also incorporated with the plaster. The result is a firm floor, upon which, in ordinary buildings, paving-tiles are laid, bedded in a tenacious cement. It must be clear that the timbers of a floor so encased could hardly be made to burn 455 even if fire were let in between the floor and ceiling. But it has been already stated that the practice of making these incombustible floors is connected with the use of walls which have no timber laid in them bedwise, and that the timber enclosures employed instead of walls, and the internal partitions, are rendered practically incom bustible, whilst the wooden staircase which economy dictates to the Parisian builders the freestone which is used in building walls being altogether too soft for the purpose is also rendered, in the manner already shown., almost unassailable by fire. It may be remarked with reference to the employment Expansion of any substance such as cinder, being of the nature of of plaster pozzuolana, or volcanic scoria, in mortar, to form a floor in floors - the manner above described (about 3 inches thick), that as all such mortars expand in setting, the walls of buildings may be forced out by the expansion of the plaster floors, if the whole surface of the floor in any story be at once covered with the mortar. A margin of 4 or 5 inches on every side should be left void until the expansion has taken place, when the floor may be completed with an assurance of close joints, and without injury to reasonably stable walls. When a boarded floor is required, as the surfaces of the true joists lie under the mortar, a base for the boards is formed of what English carpenters would call stout fillets of wood, about 2-| inches square, ranged as joists, and strutted apart to keep them in their places, over the mortar table, to which they are sometimes scribed down, and that to these fillets, or false joists, the flooring boards are secured by nails ; so that in truth the boarded floor is not at all connected with the structure of the floor, but is formed upon its upper coat of plaster. The wooden floor thus becomes a mere fitting in an apartment, and not extending beyond the room the floor might burn without communicating fire to the stairs, even if the stairs were readily ignitible. The practice now in Paris, in respect of floors, is to form Floors with the structure of wrought iron joists rolled to the form iron joists, known with us as I, T, and I iron, and to fill in with the same strong plaster between, below, and above the iron, and so to form a slab of plaster from G to 8 inches thick, according to the bearing and the depth of the iron bars the bars being enveloped in the plaster ; and the ceiling is formed as before described by laths resting on the lower flanges. In order to lighten the weight of the solid plaster, earthen pots have been placed between the joists and the spaces filled up with the mortar. The necessity which arises with us of dividing the upper Upper stories of houses into more rooms, as bed-rooms, than are partitions, commonly required in the lower stories, will be made an objection to any process that would render the partitions heavier ; but it is not in the upper stories that the lathed and plastered partition is most dangerous in respect of fire. Generally the stairs may be enclosed by solid partitions throughout almost the whole height of an ordinary dwelling- house without occasioning any inconvenience as regards the greater weight of such a partition ; and generally, too, the partition which divides the front from the back rooms of such houses may be carried up throughout the whole height of a house without removing the bearing, if the house be judiciously disposed. But even if a partition rest upon a beam or girder, a very slight addition to the scant ling of the timber will make up for the additional weight which the filling in of the partition would involve, if the materials of the core be well chosen ; and it is well known that a piece of timber placed over a void as a bressummer, and carrying a wall, resists the action of fire for a long time, and the longer if it be of oak or other hard wood. It is

not necessary, however, that the timber employed in parti-