Fig. 102. Good and faulty construction in a wall.
Masons understand the necessity of bonding stone walls, and know how to perform the work; but too often they are careless, and therefore need to be supervised. In [Fig. 102], a well bonded wall is shown at the left end, and one imperfectly bonded at the other. If the wall should chance to pull endwise a crack would appear to the right of the dotted line, since in the seven layers shown there is but one stone, A, that has sufficient contact to bond the two stones upon which it rests. The wall should also have its face and back side tied together or bonded, or it may split apart near the middle. Two walls, one of which is properly bonded, the other is not, are shown in [Fig. 103]. One layer only of stone can be shown in the diagram, but it will readily be seen that if the course which is placed on the one shown is laid like it,—that is, if the faulty bonding near the back side be continued for several courses—the wall will pull apart. The small, narrow stones have been placed at the back side of the wall, and the good stones in the front of the wall; this is all very well, but some long stones should reach from the back side of the wall to near the face, if the bond is made good. No stone should reach entirely through the wall, since in cold weather the frost will follow through such stones from face to rear.
Fig. 103. Poorly and properly bonded.
There is no economy in using mortar which is poorly mixed or that which contains too much sand and too little lime or cement. If the lime or cement, that is, the binding material, does not come into immediate contact with every particle of sand, then the mortar will be weak. If not enough of the cement or lime is used, the bond will also be weak. For stone walls not more than four parts of sand to one of cement or lime should be used. If the sand be sharp and clean a much stronger mortar is secured than when it is composed in part of rotten sand mixed with vegetable matter. If the materials are good and they are mixed in the right proportion, still good mortar will not be secured unless they be thoroughly mixed. The best masons use the least mortar, while poor masons are wasteful of it.
The prices given below are not applicable to the whole United States, but they may serve to decide the relative proportions of sand and lime which should be used, and the kind of lime which can be used most economically. Water lime retails at about eighty cents per barrel, and three parts of sand and one of lime, if the latter is fresh, should make a strong mortar. Water lime deteriorates rapidly with age, while the higher priced cements deteriorate quite slowly. Stone lime should be fresh and in no case air-slaked. It costs about one dollar a barrel and may be mixed three of sand to one of lime. Rosendale cement costs about $1.25 per barrel, and may be mixed four to one. Portland cement costs about $3 per barrel, and if used instead of the cheaper materials named above, may be mixed five to one. It should always be used for pointing walls and in the construction of cemented floors, in which case it should be mixed two or three to one. All this presupposes that the mortar is so thoroughly mixed that a lime film will surround every particle of sand.
The cement and water lime is mixed with the sand before it is wet, and this dry mixing should be most thorough, as the strength of the mortar is largely dependent on the uniform incorporation of the cement with the sand. This mixing can be much more perfectly done when the material is dry than after it is wet. Other precautions are necessary. The mortar should contain the minimum of water which will permit it to work freely, and when the mortar is used it should be solidified, that is, pushed together by means of a trowel or by the material which is laid upon it. In case of cement or grout floors, the material should be pounded thoroughly. The object of all this is to compel each particle of sand to firmly touch other particles. The tendency to “water-log” mortar, to save labor in spreading it, is too common.
If, from any cause, the basement walls must be largely of stone, the tendency for them to gather moisture may be somewhat overcome by plastering them with cement mortar, or studding may be placed against the walls upon which unmatched boards may be nailed ([Fig. 104]). The warm air of the stable cannot then reach the relatively cold walls, and little condensation will appear on the boards, since they are always more nearly the temperature of the stable than are the stone.
Wooden basement walls are preferable in all ways to those constructed of stone, grout or brick, wherever the earth does not rest against them. An excellent method of constructing the walls of the basement story is shown in a section of the first story, [Fig. 104]. The studding should be 2 × 6 inches, with short pieces of 2 × 4 placed edgewise between them to serve as outside nailing girts.
