Walls 37 



a white cement can be substituted for the 

 gray. In any case use a Portland cement. 

 To produce a black or dark gray joint, 

 mix lamp black with the mortar. Ex- 

 perimenting with a small amount will give 

 you the proportion. A beautiful wall, 

 very light in color, has been obtained by 

 using enough mortar to make a flush or 

 very nearly flush wall and then washing 

 the entire surface with a rather thin mix- 

 ture of white cement and sand. To get 

 a color even lighter, white sand is used in- 

 stead of ordinary sand. 



In masonry terminology, the walls de- 

 scribed above would be called rubble. 

 (See Fig. 12.) Rubble is the simplest and 

 least formal type ; the stones are irregular 

 in all dimensions and are laid up as they 

 come with as little breaking and splitting 

 as possible. If the stones are laid in 

 courses the wall is designated as " coursed 

 rubble." After rubble comes random 

 ashlar. Technically an ashlar is a veneer 

 of stone that is used to cover and give fin- 

 ish to a rougher wall behind. This back- 

 ing wall may be of rubble or of brick. A 

 " broken ashlar " is where the stones, while 



