In the first place, the bulk of the wall is still exposed to damp, and the moisture soaks in to within 7 or 8 inches of the interior of the building.
Again, if the wall has to carry a roof, expense is caused, as the span should be increased so as to bring the wall-plates on to the outer or substantial part of the wall, clear of the 4½-inch lining.
This may be avoided by bridging over the air-space, so as to make the wall solid at the top, which, however, renders it liable to damp in that part.
If the 4½-inch portion is placed outside, the damp is at once intercepted by the air-space, kept out of the greater portion of the wall, and at a considerable distance from the interior of the building.
The roof can be economically arranged so as to rest upon the interior thicker portion of the wall.
The stretching bond is, however, considered by some to be unsightly, unless made to appear like English or Flemish bond by using false headers, and, where the bricks are bad, the thin exterior portion, if liable to be attacked by frost, is in time destroyed.
Moreover, when the thin portion is outside, there is some difficulty in constructing deep reveals in a solid manner without their becoming a channel for damp across the opening. On the whole, however, the arrangement with the thin portion outside is the best.
Jenning's patent bonding bricks are made of vitrified pottery, and are of the shape shown in Fig. 5. These bricks are built in across the opening at horizontal intervals of about 2 feet 6 inches and vertical intervals of about 9 inches to 12 inches. The bricks in the several courses are placed chequer-wise, so that each is over the interval between two below.
Fig. 6. Scale, ½ inch = l foot.
The peculiar shape of the brick enables it to be built into the wall so that the end in the front portion is a course lower than the end in the back portion of the wall. This prevents any moisture running along the surface of the bonding brick to the interior of the wall.
When building with these bricks, it is advisable to cover them temporarily with a pipe swathed in hay bands, or by a narrow strip of wood, in order to prevent the falling mortar from lodging upon them. As the wall rises, the strip is transferred in succession from each row of bonding bricks to cover the last built in.
The bent bonding bricks shown in Figs. 5 and 6 are made in four sizes from 7 ½ inches to 13½ inches horizontal length between their ends.
Their lengths and shape are arranged so as to afford either a 3-inch or a 4½-inch cavity, and to enter the wall either 2¼ inches at both ends - 2 ¼ at one end and 4½ inches at the other - or 4½ inches at both ends.
The bonding bricks may extend right through the thin portion of the wall, or, if this is objectionable on account of appearance, their ends may be covered by bats, as shown in the figure.