It is rather a curious illustration of the practical working of injudicious fiscal laws, that the use of timber in external house con struction should have prevailed in such places as Caen, where stone is to be procured at the very gates of the town; simply because in the middle ages there was a heavy octroi, or toll, on building stone. Many local peculiarities in the use of building materials may, no doubt, be explained in the same manner ; as, for instance, the peculiar size of English bricks, or the Mansard roofs of France.
The materials used for covering the rough surfaces of walls, or for producing a smooth surface upon framed timber partitions, are either obtained from the calcination of the carbonates of lime, of the various classes of cements, or of the sulphates of lime ; and the same class of materials is, as is well known, largely applied for the purpose of con necting the small materials used for walling. The respective qualities of the LIMES, MORTARS, CEMENTS, and PLASTERS will be found under those heads, se that it may suffice here to say that, in consequence of the greater rapidity with which the real plaster (the dehydrised sul phate of lime) sets, it is always employed internally to render or cover the walls or partitions, when that can be done economically. It is required, in such cases, to produce an even surface to receive the wall decorations, which surface should at the same time be so far absorbent and non-conducting as not to allow the moisture in suspension in the rooms to condense upon, or to remain upon, the sides of the rooms; and for this purpose the real plasters possess properties which no other materials can boast of. In the greater part of Europe, however, plaster is both rare and costly, and its place is supplied, more or lees satis factorily, by the lime and hair, and the fine stuff, as our plasterers designate the various descriptions of coats they obtain from the purer carbonates of lime treated in peculiar manners, according to the par ticular parts of the operation. The hydraulic cements are sometimes used for internal plastering or wall decorations, when moisture is to be contended with ; and the oddly named artificial cements obtained by the second calcination of the sulphates of lime, such as the Keene's, Parian, or Martin's cemeuts, are used for ekirtings or for wall deco rations, when particularly hard close surfaces are required, and it may be necessary to paint them immediately. The plasters do not resist the action of the external atmosphere, or its changes of hygrometric state, although when proper precautions are taken the plaster of Paris stands tolerably well on external walls near that town ; but, as a general rule, none but the hydraulic cements should be used for this particular deathiption of work, and even with them it is essential to prevent moisture from lodging upon their surfaces, especially in climates exposed to sudden frosts and to heavy winter rains. Nearly all this class of materials requires to be protected by a coating of oil-paint, or of some other preparation able to oppose the absorptiou of water.
Roofs are covered in various ways, depcndiug mainly upon the economical conditions of the locality,—namely, either by thatching with straw or reeds, by shingles, by tiles, by slates, or by one or other of the metals, iron, zinc, copper, lead, or tin ; and, in very temporary buildings, even by tarred felt. Thatching makes a warm and au
exceedingly picturesque covering; but it is objectionable on account of its retaining moisture under some circumstances, of its weight, and of its inflammable nature. In America and in Norway small wooden slabs, cut like slates, are used, under the name of shingles, and if pro perly nailed and weighted down in positions exposed to violent wiuds they auswer tolerably well, though, of course, they are exposed to the same objection as the one above alluded to—namely, their inflam mability. Shingle roofs were formerly common iu England, and specimens yet remain on some church spires. • In all densely peopled districts, therefore, slates or tiles are used for the commoner descrip tions of houses, and the metals aro used for more important buildings under the conditions discussed under ROOF. Tho precautions to be observed in all these cases are—I, that an efficient circulation of air should be kept up within the roof ; 2, that when metals are used, the contraction and expansion should not be interfered with ; and 3, that when two metals are employed, they should be placed in such manner as not to allow a destructive galvanic action to take place.
Metals are also used in building operations in other modes than simply as coverings, and iron in Its various forma has of late become an article of the greatest importance to the constructive or to the decorative builder. Cast-iron is largely used for girders, columns, railings, pipes, sashes, &c. ; wrought-iron is becoming daily of more and more imports anco for girders, for roof framing, for pillars, railings, tanks, doors, and countless purposes of common life. Lead, copper, sloe, tin, and their allova are used for many details of building, and for the distribution of those essential elements of modern comfort, gas and water: precautions, however, are requisite in their application to secure them from certain chemical actions which may be produced by the extraneous matters contained in the fluids so distributed. [WATER Surety.] It would appear that if the new metal aluminium were obtainable at a cheap rate, it would constitute one of the most valuable additions to tho,list of building materials, on account of its lightness, its tenacity, and its powers of resisting the action of the atmosphere.
Glass in its various forma is a material so generally known that it will be sufficient merely to mention it ; and the use of oil-paints for purposes of decoration or of preservation will be discussed under PAINT. The use of the solutions of silica, and of the other various substances applied of late years for the protection of woods from wet and dry rot, will be noticed under the article PRESERVATION OF STONE AND WOOD, already referred to. Wall linings, or PAPER HANGINGS, Will be noticed under the latter head.