21 



MATERIALS FOR BUILDING. 



MATERIALS FOR BUILDING. 



are exposed to decay in the open air, on account of the differences in 

 the molecular structure of their constituent elements. 



Many of these remarks will apply to the choice of bricks for 

 building purposes ; for their relative values will depend upon their 

 powers of resisting the transmission of water, their non-conducting 

 powers, and their durability under the ordinary action of the atmos- 

 phere, when exposed for a long time to its effects. In many cases walls 

 have been, and still are, executed of unbumt clay, either rammed into 

 moulds which enclose the space to be occupied by the wall itself (in 

 the manner used in the western counties of England, where it is known 

 by the name of cobb icatlins/), or in the form of unbumt bricks (as in 

 the walls of Assyria and of parts of Egypt) , and when due precautions 

 are taken to isolate the lower parts of such walls from the ground, 

 and to protect them from heavy rains, they certainly make very warm 

 and comfortable even though temporary structures. The total dis- 

 appearance of the domestic structures of the nations of antiquity which 

 adopted the use of unburnt clay, whilst the structures erected at the 

 same period of the more durable burnt bricks have survived to our 

 tunes, prove (if such proof were needed) that the latter alone should 

 be employed in buildings which are likely to be long exposed to 

 distinctly marked atmospheric influences. In fact, no mere 

 mechanical preparation of the silicates of alumina (the base of all clays) 

 can give those materials the property of a permanent cohesion ; and no 

 stable combination between the various elements can be effected, 

 without the intervention of fire ; or, in other words, the pyrogenous 

 combination of silica and alumina are the only stable ones. A small 

 proportion of the carbonate of lime in clays is a desirable condition ; 

 for it facilitates the fusion of the other ingredients ; but a large pro- 

 portion of carbonate of lime entails inconveniences which have already 

 been alluded to. [BRICK.] It may be suspected that much of the 

 value of brickwork depends upon the reaction of the bricks themselves 

 upon the mortars, or upon the cementing materials employed ; and it 

 would therefore seem that, for the purposes of hydraulic engineering, 

 or of building in water, it is desirable to use bricks which, even after 

 calcination, retain a certain proportion of soluble silica, in a state to 

 allow of its being taken up by the lime around it. The remarkable 

 preservation of the underburnt Roman bricks, or of the soft kiln-burnt 

 bricks of the middle ages, when used in positions where running 

 waters could not affect them, may be explained by the fact of the 

 existence of some statical chemical balance of this description. For 

 general purposes however, it may be sufficient here to state that the 

 hardest, and most thoroughly burnt, bricks only ought to be used in 

 the exposed faces of walls ; that only the best hydraulic limes [LIME ; 

 MORTAR] should be used in conjunction with them ; and that, without 

 entering into any abstract calculations of stability, no external walls of 

 houses in exposed positions, should ever be constructed of less thick- 

 ness than of one and a half brick; so as in fact to intercept the 

 passage of water from the exterior to the interior by a vertical joint of 

 mortar. The combination of brickwork and of timber sometimes 

 admits of the attainment of the latter condition, when the total thick- 

 ness does not exceed that of one brick ; but in this case the bond of 

 the work cannot be theoretically satisfactory. 



In many of our colonies, and in many well wooded countries of a 

 more ancient date, the use of timber fur external walls takes place to a 

 great extent; nor, provided that the passage of moisture from the 

 ground, by capillary action, be intercepted, that the rain be prevented 

 from lodging on the upper surfaces, and that there be no danger from 

 the communication of fire, can there be any rational objection to this 

 mode of construction. Where wood is very abundant, as in the United 

 States, Norway, &c., it is used simply in logs ; and those logs are laid 

 upon one another without being squared, but are only halved together 

 at the angles ; the interstices are then filled in with clay, or with lime 

 and hair ; and the exterior and interior surfaces of the walls thus 

 formed, are then carefully plastered. In countries where wood is 

 more valuable, the style of construction becomes more elaborate, 

 and the framing is executed with squared timber, either filled in with 

 brickwork-panels, called technically " brick-nogging," or with quarter- 

 ings, which are subsequently either covered by " shingles," (or small 

 thin pieces of wood laid like slates,) or are boarded, or lathed and 

 plastered. The half timbered houses in our own country, and in Nor- 

 mandy, may be referred to as illustrations of all these last named 

 varieties of wooden construction ; and of the remarkably picturesque 

 eftects they were able to produce. The Swiss clt&let of the present day 

 are equally worthy of admiration ; and it may be worth while to add 

 that when the exposed timbers of such half timbered houses are 

 covered by slates, aa is very frequently the case in our own southern 

 provinces, they are but little exposed to the danger of decay, or of fire ; 

 out no such palliations of the defects inherent to wood structures can 

 ever guarantee them against the attacks of insects or of vermin. 



The principal use of wood is, however, for internal works and fittings ; 

 and the selection of the particular description to be used in any 

 position must be regulated by so many local considerations that it is 

 preferable to treat of them in two separate articles. [Wooos, 

 Buri.Diua ; and WOODS, FCRMTURE.] The general conditions for their 

 selection and ue are, that the woods should be as light and as easily 

 worked as possible, consistently with the requisite degree of strength ; 

 that when intended to be used as girders, or for framed carpentry, 

 they should be of a straight, tough, fibrous nature; that the trees 



should be felled in the winter, and that, under all circumstances, the 

 wood should not be fixed in a building until the sap, or other moisture 

 it might contain, had been allowed to escape; that a free circulation 

 of air should be maintained around the woodwork of every description ; 

 and that especially all contact with a damp, confined, atmosphere 

 should be avoided. As might naturally be expected, woods transmit 

 moisture more easily in the directions of their vesicles, than trans- 

 versally to the latter ; and attention must be paid to this law when- 

 ever it may be necessary to employ this material partially in and out 

 of the ground. The attacks of insects, and of the marine boring worms, 

 together with the conditions of decay under the action of wet or of 

 dry rot, must not be overlooked in the inquiry into the value of woods ; 

 they are discussed under PRESERVATION OF STONE AND WOOD. A 

 very essential property in woods used for decorative works is that they 

 should not be exposed in any serious manner to absorb atmospheric, 

 or in fact any external, moisture ; and that they should not warp under 

 changes of temperature. To a certain extent, all woods are exposed 

 to this inconvenience ; but the superior descriptions of mahogany, 

 oak, and fir, do not warp in any serious or dangerous manner 

 under ordinary changes, provided that due care has been observed in 

 then- seasoning before placing them in the work. Some woods again 

 have a distinct action upon metals, such as the oak produces upon 

 iron, or even occasionally upon lead; but the circumstances under 

 which this action takes place are not sufficiently knowu to warrant any 

 decided general observations with respect to it. Contact with other 

 building materials does not seem to affect the durability of wood, 

 provided the circulation of air around the latter be not prevented. 



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, so 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 

 material* can boast of. In the greater part of Europe, however, plaster 

 is both rare and costly, and its place is supplied, more or less 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 cements, are used for skirtings 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 

 description 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 absorption of water. 



Roofs are covered in various ways, depending 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 an 

 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 ehinyles, and if pro- 

 perly nailed and weighted down in positions exposed to violent winds 

 they answer 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 in 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 are used for more important buildings 



