BUILDING NEW HOUSES 65 



reinforced with steel rods and Fig. 15 a section of a 

 house with solid walls. 



The difficulty of building the walls in this way is that 

 being porous, moisture and cold readily pass through 

 and the inner surface can only be made warm and dry 

 by building up an inner frame or putting up furring upon 

 which to plaster, leaving an air space between the wall 

 and the inside surface. In building up walls in this way 

 more or less large stones are sometimes laid and the 

 cement filled in, carefully working it in and about them 

 so that no air spaces will hold to the plank or stones. 



The Block System. 



By the block system the cement is put into moulds 

 of the desired form and size for the various parts of the 

 building. These blocks may be made to represent cut or 

 rough stone, the corners, window frames, sills, and caps, 

 etc., being either plain or ornamented. Air spaces are 

 obtained by having vertical openings which shall be 

 continuous from underpinning, or by having the walls 

 made of double blocks with narrow boards or planks 

 placed perpendicularly at the joints, thus making an 

 entirely hollow wall. The latter makes by far the best 

 non-conducting wall and the blocks are less complicated 

 in structure, though double the number are required in 

 the building. One of the advantages of the block system 

 is that a few blocks may be made at a time as one has 

 the leisure, and are just as good, possibly better, if one 

 is a year in making enough for a house. Fig. 16 illus- 

 trates a house made of concrete blocks, and Fig. 17 a 

 machine by which the blocks are made. 



The Cement and Sand. 



Good work cannot be made of cement more than six 

 months old as it is ordinarily kept, but if it has been 



