CONSTRUCTION NOTES 261 



2 or 3 inches) or where the natural foundation soil is of gravel or sand, 

 sufficiently porous, the wearing surface (brick, concrete, cobblestone, 

 stepping-stones, etc.) may be laid on the prepared subgrade of the original 

 soil. In no instance, if a foundation is desired for added safety, should this 

 foundation course under such conditions exceed a depth of two or three 

 inches of cinders or similar material. In every instance where a founda- 

 tion course is necessary (see figures 1-4, Plate no) this course should be 

 put in place in layers, approximating not more than four inches in depth, 

 and each layer should be thoroughly wetted and tamped or rolled and 

 brought to an even surface parallel with the proposed finished grade, and 

 at the required depth below the surface of the walk. 



Walks with a wearing surface of brick, concrete, cobblestones and 

 medina block may be laid either upon a foundation consisting only of 

 porous material, or upon a concrete foundation (see 4^). The other types 

 of walks are almost never laid upon concrete foundation, with the exception 

 of tile walks, which should never be laid upon any other foundation than 

 concrete. The wearing surface of any walk r with the exception of tanbark 

 walks, should be firm, of an even grade within the limits allowed by surface 

 drainage requirements, and of a suitable texture and color to meet the 

 requirements imposed by its use and appearance. The wearing surface 

 should also have a firm bond with its base course; especially is this true in 

 the construction of walks where a bond between the foundation course and 

 the wearing course is by means of cement. Inasmuch as the great differen- 

 tiation in walk construction occurs largely in the problem of completing 

 the foundation course and the wearing surface, each of these walks will 

 be discussed from this point on as a separate type with its individual prob- 

 lems, although in a small part these problems may be similar. 



(ad) Brick walks on concrete base (foundation courses and wearing sur- 

 face}. Walks of brick may be constructed on a concrete base with a cinder 

 foundation, or on a sand cushion with a cinder foundation. On the sub- 

 grade prepared in accordance with the previous instructions and at a depth 

 of approximately twelve to fourteen inches below the finished grade of the 

 walk (see figure 3, Plate 109) a foundation course of cinders is put in place 

 as specified heretofore in two layers of equal depth, making a total depth 

 of six inches at the side of the walk when thoroughly watered and tamped 

 or rolled. On this foundation course thus prepared is placed a base course 

 of concrete (1:3:5 mixture), bringing the surface of this concrete to the 

 required lines and grades, allowing proper provision for the economical con- 

 struction of a brick curb or concrete curb (figures I and 2, Plate in) if 

 such is required. On this concrete foundation thus prepared and after the 

 concrete has been given twenty-four hours for setting, the brick is laid in 



