In rubble work the stones are rough and unhewn. They must be laid upon a good bed of stiff mortar with their stratifications in a horizontal position. Otherwise, the face of the wall might "peel" from the effects of frost and moisture, making an unsightly as well as a weaker wall. The term "ashlar" refers to a wall builded of stones having finished faces. When either rubble work or ashlar is laid up in courses it is known as coursed rubble or coursed ashlar. When the horizontal joints are not continuous the wall is known as random rubble or broken ashlar.
Not infrequently a wall will be constructed with an ashlar facing attached to a brick backing by means of metal bonds. In such a wall, the faced ashlar, unless more than 8 inches in thickness and well bonded into the wall, should not be considered in estimating the strength of the wall.
Fig. 12. "Form" for Concrete
In the construction of both brick and stone walls the work should be carried up as nearly as possible at the same levels. In both brick and stone walls the corners are run up with stepped courses, the corners being plumbed as the wall is carried upward. A line is then stretched between the corners and, layer by layer, the rest of the wall filled in. No corner should, ordinarily, be carried more than 3 feet above the rest of the wall. In the case of uncoursed stone work the wall is leveled every 15 to 18 inches in its height.
6. Forms for Concrete Walls.—The economical building of forms for concrete walls is a matter of importance in building construction. [Fig. 12] shows a type of form suitable for foundation work. Such forms should be made of semi-seasoned stock. Thoroughly seasoned stock will warp badly when the wet concrete is placed. Spruce, Norway pine, etc., are better woods to use than hard or Georgia pine.
For ordinary foundation work 1-inch boards may be used, the studs being placed not over 2 feet apart. These studs may be assisted materially in holding the forms in position, by wires placed as in [Fig. 12], and by props placed against the dirt wall of the excavation.
In placing the concrete a 4-inch layer is laid and then "spaded" or "worked" well into place, a "wet mix" being used. The smoothness of the resulting faces is increased by an additional spading of the mixture away from the form. A good spading tool is made by straightening out an ordinary garden hoe. This allows the cement and mortar to flow next to the form and hold this place while the filling proceeds.
Where forms are placed to give finished walls, that is, walls to which no plaster is to be applied, they should be aligned with no greater variation than ⅜" from the lines specified.
Forms should be allowed to remain until the concrete will resist indentation with the thumb, upon ordinary walls.