Fig. 2.

City houses are constructed in very much the same manner as country houses, with stud partitions and wooden beams; but the beams rest at their outer end on brick walls instead of studding.

This structure, of beams, studs, rafters, and stone or brick walls, is liable to various kinds of deterioration, and the symptoms of such deterioration should be known, in order that the disease which they indicate may be treated before it becomes serious. In a brick house settlements of the walls may take place, due, usually, to inadequate foundation. Such settlements are indicated by cracks, the direction of which is, as a rule, approximately at right angles with the direction of the settlement; so that, by drawing lines perpendicular to the general direction of the cracks, the position of the yielding portion of the foundation can generally be found, and the trouble remedied in such manner as circumstances may require.

In a wooden house, the weight of which is trifling in comparison with that of a brick one, settlements, which will show themselves by cracks in the interior plastering, rather than by dislocations of the outside clapboards or shingles, are less likely to proceed from the failure of the foundation than from rotting or shrinkage of the timbers, or from their insufficient strength. Settlement from rotting of timbers occurs most commonly in old houses, and manifests itself first, as a rule, in the outside walls, the studs of which stand on the sill. As the sill rests on the stone or brick underpinning, which is often damp, particularly in old houses, where the ground outside is frequently graded up so high as to cover the underpinning, and even portions of the sill, the latter soon begins to rot on the under side; and, when the disease has progressed far enough, the timber slowly gives way. When this happens, the studs resting on the decaying timber sink, and the disorder is betrayed by the cracking of the plastering incident to the movement. In building new houses, the rotting of the sill can be postponed for many years by painting the under side with a coat of any cheap paint which will repel the dampness of the stone or brickwork on which it rests; but in old houses, where it has already occurred, the remedy is to cut out the old sill, or such portions of it as may be decayed, and put in fresh timber, which can be done with little difficulty if settlement has not progressed too far.

City houses.

Structural diseases.

Defects due to shrinkage show themselves, in general, within two years after the completion of the house, when the timber has been dried by the furnace fires or steam heat of one or two winters. As all wooden houses are now framed with green timber, a shrinkage of at least a third of an inch must be expected in every floor timber of average depth; and where a girder rests on piers, and floor-beams on the girder, the combined shrinkage of the girder and the beam may be two-thirds of an inch. If, then, as often happens, a partition is secured at one end to the framing of an outside wall, which shrinks very little, if at all, and is supported at the other end by a beam, resting on a girder, and exposed to the dry air of the house, this end will, by the shrinkage of the beam and girder, settle half an inch or more, distorting the openings, causing the doors to bind, and cracking the plastering.

Shrinkage.

Where beams, girders, and stud partitions are superposed through several stories, the shrinkage accumulates, so that cracks in plastering, and other marks of settlement, are always worst in the upper story of a house. A skilful architect can frame a house so as nearly to eliminate settlement from shrinkage, or, at least, to make it uniform, so as not to distort the partitions; but, if this has not been provided for in the original construction, no remedy can be applied. Fortunately, settlement from shrinkage reaches its limit in a few years, and the cracks can then be stopped up.

Settlement from weakness of timbers is a much more serious affair. It can usually be distinguished by the bending of floors, or ceilings, or girders, at the weak point; and, unless checked, will continue to increase indefinitely. The only remedy is the application of supports to relieve the overstrained beams or girders; and these supports may take the form of additional piers under girders, or extra timbers, braces, or arches under floor-beams; but they should be applied at once.

Weakness of timbers.

Apart from the dislocations proceeding from settlement, all houses with wooden floor-beams and partitions are liable to cracks in the plastering due to other causes. The most serious of these come from the deterioration, or original bad quality, of the plastering itself. In most houses the plaster is spread on wooden laths, about one and a half inches wide, and three-eighths of an inch thick, nailed to the studding or furring strips, with a space between them, which should be three-eighths of an inch wide, or just the thickness of an ordinary lath. The mortar for the first coat of plastering on laths is mixed with hair, or, occasionally, with wood fibre. When applied to the laths, and pressed against them by trowelling, the soft mortar is forced through the spaces between them (Fig. 3), and bends over, forming, when hard, hooks, or "keys," or "clinches." The mortar, after drying, does not adhere to the laths, and the keys or clinches are all that holds the sheet of plastering in place; and, as the plastering mortar, when dry, is brittle, even that would be insufficient if it were not for the hair or other fibre mixed in it to give it the necessary tenacity. Inferior plasterers, to save the mortar which forms the clinches, put on the laths one-fourth of an inch apart, or even less. The trowelling then fails to push the soft mortar through the space in sufficient quantity to bend over, and much less mortar is used; but the result is that the wall or ceiling, when finished, has little or nothing to hold it to the laths, and when these dry and shrink, as they soon do, the plastering separates from them, bulging out from walls, or "bagging" down from ceilings. Even where the plastering was originally good, the shaking incident to walking or running over the floors above will, in the course of years, break off the clinches of ceilings, allowing the plastering to separate from the laths. In either case fine cracks can be observed, running at random over the ceiling, and, by holding a straight rod under it, the plastering can be seen to have " bagged "; and, by pressing it with the hand, or with a ' stick, the sheet of plaster, which, having left the laths, is supported only by the tenacity of the hair in it, can be felt to yield. A plaster ceiling which has left the laths in this way is not necessarily in a dangerous condition. If originally well made, with plenty of good hair, a sheet of plastering mortar of considerable extent may hang for several years without support from the laths; and, as the breakage of the clinches goes on progressively over a ceiling, it may be a long time before the whole is affected. When, however, the bulging becomes very marked, and the bulged portion is much cracked, it is liable to fall, and should be taken down, the old mortar picked out of the spaces between the laths, and the ceiling replastered; or, still better, the old wooden laths taken off, and the ceiling replastered on metal lath, which will hold the mortar indefinitely.

Fig. 3.

Defects in plastering.

Another, but less serious cause of cracks in plastering is the shrinkage of the laths. The lathers, to save themselves trouble, often change the direction of a few laths on a wall or ceiling (Fig. 4), instead of cutting short pieces, and putting them on parallel to the general direction of the lathing. Every such change of direction causes, later, a crack in the plastering over it; and similar cracks are common at the corners of door openings, where, unless special precautions are taken in lathing, the shrinkage of the heavy studding around the doors affects the plastering. Still other cracks are often seen in the plastering around chimneys, due to the settlement of the brickwork of the chimney, which, as the mortar in the joints dries out, settles slightly away from the wood framing around it. A different set of cracks is usually to be observed around staircases, which, owing to the peculiar character of their framing, settle much more by the drying and shrinkage of their supporting timbers than the work about them. The same may be said of plastering in attic rooms, where, owing to the special effect of shrinkage on the rafters, and other members of the roof-framing, cracks are almost inevitable. In all these cases, however, they are of no serious consequence, involving, at most, only an occasional filling with plaster of Paris.

Fig. 4.