When it is necessary to ram foundations, the stone, being previously chopped or hammer-dressed, so as to have them as little taper as possible, should he laid of a breadth propor tioned to the weight intended to he rested on them. mill rammed closely together with a heavy rammer. In ordinary eases, the lower bed of stones may project about a foot on each side of the wall, on which another course may lie laid, so as to bring the upper lied stones upon a general level with that of the trench, projecting about eight inches on either side of the wall, or receding four inches on each side within the lower course. Care should lie taken that the joints or every upper course fill as nearly as possible upon the middle of the stones in the course immediately beneath it ; a pi ineiple also to lie strictly adhered to in every kind of walling ; for in all the nodes, various as they are, of laying stones or bricks, the uniform object is to obtain the greatest lap one upon the other.
The directions for preparing a solid foundation, refer to the general practice amongst builders before the introduction of concrete. The now almost universal use of the latter, as a certain, convenient, and ready means of obtaining a secure foundation, has rendered it necessary to give a description of the mode in whi•h this material is generally used.
The ground having been examined as described in the first part of this article, a sufficient depth must be excavated in the bottom of the trenches, to allow of throwing in a quail 1 tits of et aterete, varying in breadth and depth, aci•ording to . the size and character of the building to be erected, the reeessary width of the filotings.
The concrete is eomposed of ditThrent materials• and pro .
portions of those materials, as the qualities of sand, lime, are most conveniently obtained in the locality of the building.
The concrete used in and near London is generally composed of Thames ballast and flesh burned (ground to powder without slacking,) in the proportions of 'rotu one-fifth to one.ninth of lime to one of the ballast. These ingredients should be well blended together dry, and as small a quantity of water added as will bring them to the consistency of mor tar; and then, after tinning over the materials with the shovel once or twice, thrown as quickly as possible into the foundation, from a height of several feet. It sets very quickly, so that it is desirable that the mixture should be made at, or close to the height from which it is thrown, and then spread and brought to a level as expeditiously as pos sibie. See CONCRETE.
Having premised thus much on foundations, we proceed to the operation of walling; the first object in a hidi is the due preparation of the cementing material.
Mortar is most commonly used in modern brick buildings. It is composed of lime, gray or White:but gray or stone-lime is the better, mixed with river-sand, or road-sand. in the proportion of one of gray lime to two and a half of sand, and one of white or ehalk-lime to two of sand.
In slacking the lime, no more w ater should lie used than is barely sufficient to reduce it to powder; and it should be covered with a layer of sand, in order to prevent the gas, wherein is the virtue of the lime, from flying oil: It is best to slack the lime in small quantities, about a bushel at a time, in order to secure its qualities in the mortar, which would evaporate were it to remain slacked any length of time before being used, See MORTAR.
The mortar, a hen about to be used. should be beaten three or flair times, and turned over with the beater, so as to incorporate the lime and sand, and break the knots that pass through the sieve : this not only renders the texture more uniform, but by admitting the air into the body and pores of the mortar, makes it much stronger. Should the mortar stand any length of time after this operation, without being used, it must be beaten again : it should be observed, that in these beatings very little water should be used ; though in hot and dry- weather the mortar may be kept considerably softer than in winter.
In dry weather, and for firm work, the best mortar must be used, and the bricks should he \vetted, or clipped in water as they are laid ; but in damp Weather, the latter precaution Will be unnecessary. The wetting of the bricks causes them to adhere to the mortar, which they will never do it' laid dry, and covered with sand or dust, as they may be removed With Oat the adhesion of a single particle of the mortar.
In laying the foundations of walls, the first courses are always laid broader than the wall intended to be carried up; those courses are called the and the projections are called set-oil's; there are generally two inches in each pro jection.
In working up the wall, not more than four or five feet of any part should he built at a time ; for as all walls shrink immediately after building, the part which is first brought up will settle before the adjacent part is brought up to it ; and the shrinking of the latter will consequently cause the two parts to separate. Unless it be to accommodate the carpenter, &c., no part of a wall should he carried higher than one seaff(dd, without having its contingent parts added to it. In carrying up ally particular part, the ends should be regularly sloped oft; so as to receive the bond of the parts, on the right and left.