40 FARM BUILDINGS IN SOUTH AFRICA 



pressure comes upon it, and tend to burst the masonry apart. The com- 

 pressive strength of rough rubble scarcely exceeds that of the mortar 

 used, but wherever possible stone, even though in the form of spalls, 

 should be used in preference to mortar, so as to preserve the strength and 

 prevent excessive settlement. 



Squared Rubble, or Snecked Rubble (see Fig. 32). — The stones for 

 masonry of this class are roughly squared by means of a stone-hammer, 

 to show horizontal and vertical joints when built into the wall. Stones 

 squared in this way are said to be hammer-dressed. As shown in the 

 illustration the dressing of the stones to form vertical joints is confined 

 to the first two or three inches back from the face, the tails of the stones 

 being left rough. 



Block-stone Masonry. — If the stones be squared all over with the 

 hammer, and neatly fitted together without the insertion of spalls, so 

 as to give vertical and horizontal joints in the interior, as well as on 

 the faces, of the wall, the work is called " block-stone masonry." This 

 class of masonry may be looked upon as lying between rubble and 

 ashlar. 



