Its friends claim that it is stiffer than a solid wall of the same amount of brick; that it offers a better insulation, by reason of the air space, against cold and dampness; and that therefore it saves the necessity of furring and fire stops on the interior wall surface. On the other hand, admitting the value of the air space and the consequent saving of furring, objection is made that the air space is apt to get filled with mortar and brick chips during construction; that the metal ties, unless heavily galvanized or dipped in asphaltum, rust out in a comparatively short time; and that it is not as strong a bearing wall as the solid wall of the same brick content. Mr. Arthur W. Joslin, a contractor and builder of Boston, whose extensive practice gives his judgment weight, says in summing up the pros and cons: "The 10-inch vaulted wall is strong enough for ordinary dwellings, even though the ties do rust out, unless it is built out of the poorest kind of brick with very poor mortar. In my opinion, a vaulted wall, if properly built, the vault not filled up with droppings, and provisions made for ventilating from the inside, is an ideal wall for dwelling house construction, but I would not recommend it for buildings for other purposes where there would be more or less of a dead load coming on the floors." On the matter of comparative costs, Mr. Joslin adds: "It is cheaper to build an 8-inch solid than a 10-inch vaulted wall, and slightly cheaper to build a 10-inch vaulted than a 12-inch solid wall."
The accompanying drawing shows a cross section of this type of brick wall. Except in a few particulars, its construction does not differ essentially from that of the solid brick wall as already described.
A 12-inch brick foundation is wide enough for the 10-inch wall and a 16-inch foundation for the 14-inch wall. The metal ties, heavily galvanized or coated with asphaltum, should be placed about 18 inches apart at every fifth or sixth course and extend at least 2 inches into the mortar joints.
Fire stops are not needed, nor is furring, as the plaster may be laid directly on the brick. In order to preserve the chief merit of this type of brick wall, great care should be taken, during construction, that the 2-inch air space be not allowed to fill up with mortar and brick chips.
[FACE BRICK ON HOLLOW TILE CONSTRUCTION]
The local ordinances in some municipalities require thicker walls with hollow tile construction than where common brick backing is used, which affects the comparative cost of the buildings; but, where the total thickness may be kept the same as for solid brick, the cost is practically the same, with slight differences one way or the other in different communities. The tile used for backing may be either soft or hard burned, but never with an absorption of over 12 per cent, and are scored variously so that there may always be a good keying surface for plaster. These tile may be set with the hollow spaces or cells running either horizontally or vertically, as the case demands or the builder chooses.
Construction
Walls of this form of construction are built in much the same manner as walls with common brick backing, except that it is always desirable to use cement mortar with the tile to insure the needed strength of bond. The face brick are first carried up four or five courses and then the hollow tile units, of whatever thickness chosen, are laid up behind the brick, leaving an inch space between the tile and brick ([Fig. 31]). The tile are laid, with broken joint as in running bond, in a half-inch mortar bed. When the tile width is over 4 inches, the mortar should be spread only on the front and back edges of the tile, leaving a hollow space in the center. In the vertical joints only the front and back webs require mortar. If vertical tile are used all the webs should be well mortared, while the vertical joints are simply buttered.
Care must be taken that the space between the tile and brick does not get filled up with mortar, for this would defeat its purpose of serving as an insulation against moisture and cold. With this one-inch space between brick and tile open, furring and lathing are saved, as the plaster may be directly laid on the tile and the necessity of fire stops avoided.