Dwellings and Damp.

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CHAPTER XIX.

"Houses are built to live in, not to look on; therefore let use be preferred before uniformity, except where both may be had.”—Lord Bacon.

In Lower Bengal all houses, however well raised from the ground, are more or less damp in the rains.

Even in the best built European dwellings, raised on arches, it may be five to six feet from foundation level, the unmistakable damp line makes its appearance both on the outer and inner walls as soon as the rains have lasted long enough to saturate the subsoil on which the foundations rest. This is owing to the clay soil which retains moisture even in well-drained localities, and to the materials of which our houses are constructed being of a spongy and absorbent nature. The hardest and best burnt brick will absorb one-sixteenth of its weight of water, and the softer and more porous the brick, the greater quantity will it drink up.

The brickwork, therefore, being in immediate contact with the wet subsoil, the damp rises in the walls by capillary attraction until it reaches the line of evaporation. As both the soil and the materials of buildings are often saturated with nitrous salts, the latter crystallise as the moisture evaporates, and their bulk being thus increased, they burst the pores in which they are contained and the

202.

Effects of Nitrous Salts.

disintegrated plaster and brick crumble away, causing that unsightly desquamation and dilapidation so common in the basement walls of ordinary buildings and especially in inferior native houses.

It will be observed that this crumbling away does not take place at the foot of the walls or pillars, but at some distance from the ground, and that if the lower part be protected by a coating of Portland cement, the line of evaporation and erosion only mounts higher, but this deteriorative action is not prevented from taking place. The extent to which this disfiguration, and ultimate ruin

of buildings, goes, is shown by the above sketch, which represents the state of many buildings familiar to every resident in a Lower Bengal town. This state of things is due either to ignorance or heedlessness on the part of the builders in neglecting during the construction to insert a damp-proof material as the last course of the

Damp-proof Courses.

203

plinth. Several plans have been tried with more or less success to prevent damp from rising in the walls, and to remedy or hide it when present, and the lower stories of many otherwise comfortable houses are rendered uninhabitable or unsightly from failure to accomplish this. Portland cement plastering, high dados of dark coloured silicate paints have all been tried, but still the nitrous efflorescence appears, and the damp line mounts higher and higher till it can escape into the air by evaporation. Silicate paint, though better than the ordinary paints, is inefficacious where there is much nitre in the walls. The following, which is a Russian recipe, may be tried with advantage: Make a boiling solution of two seers of green vitriol (or copperas) to fifty seers of water, or about twelve gallons; add one seer white resin, five seers of sifted red or yellow ochre, four seers of rye meal (or coarse country flour), and three and-a-half seers of linseed oil; stir the whole together till the ingredients are thoroughly incorporated, and apply two coats while hot, allowing the first to dry before applying the second. The mixture must be applied in dry weather while the walls are free from damp: a coat of silicate paint of any desired color may be afterwards applied. Complete prevention, however, is only applicable at the time of construction, and it is effected by the insertion of a dampproof course or a layer of some non-absorbent impervious material or composition between the foundation and superstructure. Various substances have been used or suggested for this purpose. Sheet-lead or sheet-copper would perhaps be the best materials, being indestructible, perfectly impervious to damp, and neither apt to break nor crack beneath superincumbent and unequal pressure, but

204

Material for Damp-proof Courses.

their expense is quite against their general use. I once knew a case where a German engineer, in charge of buildings near Calcutta, put sheets of plate glass in the wall of a building as a damp-proof layer, I fear without much success, as the unequal settlement of the building and the weight of the superstructure must have reduced it to fragments. In those days De la Bastie's process of toughening glass was not known, and it may now be well worth ascertaining whether toughened glass tiles or slabs manufactured from blast furnace slag by De la Bastie's or Siemen's process, might not be introduced into buildings for damp-proof courses with every prospect of success; as if the glass thus produced is sufficiently tough for railway sleepers, it would surely be quite capable of bearing the inert pressure of the weight of a building. Slag bricks, enamelled bricks, and vitrified stone-ware perforated tiles, as recommended by Eassie, are also now manufactured. The material most commonly used in this country is Seyssel Asphalte, but it has several disadvantages, the principal being its aptitude to soften at a high temperature and its compressibility, the great pressure of the superstructure squeezing and forcing the yielding material from between the joints which interferes with its successful action as a damp preventer, and the superstructure of buildings has even been known to slip from the softening of the asphalte in hot weather. An useful but little known composition for the purpose is a mixture of fresh slaked lime and vegetable oil. This must be well mixed by hand the day before it is wanted for use. It is then to be spread evenly over the foundation course with a trowel in a layer about three-quarters of an inch thick, and after it has been left for a day

Damp Houses never Healthy.

205

or so to set firm, the building may proceed, care being taken in laying the first courses of brick not to break up or disturb the cement. A damp-proof course may also be laid with bricks, which, after being heated, have been plunged into a bath of boiling coaltar and then rolled in dry sand. It will add little to the first cost, but greatly to the stability and good appearance of houses generally, if the basements are plastered with Portland cement instead of the ordinary sand plaster; and the extended manufacture of cement in this country, especially by the Indian Cement Company, will tend to bring the material into more general use. Damp houses can never be healthy houses, moisture being a necessary factor in the process of decomposition of organic matters in the soil, which give rise to malaria and consequent danger to health. A house built on a damp site, without a dampproof course, and with walls often of insufficient thickness, exposed to heavy driving rains, lasting as they sometimes do in the tropics for days together, cannot fail to be unhealthy; the damp is absorbed by the walls and given off in vapour inside the rooms. Thus during the rains in Bengal we find our boots, books, and everything made of leather covered with green mould, and falling to pieces, while clothes refuse to dry, and all our surroundings feel damp and clammy. Pictures hung against the walls become irretrievably ruined, and every piece of furniture or cabinet-work with glued joints falls asunder.

Every house should be surrounded with a well-constructed stone or brick drain, well cemented with Portland cement, to carry off the water streaming down the outer walls and which would otherwise lodge about the