CHAPTER XI 



PLASTER OF PABIS 



I HOUGH less important than lime, plaster of 

 Paris is nevertheless much used in building, 

 especially for ceilings, molded ohimney-pieces, and 

 in the filling of cracks and cavities. It is a white 

 powder which is made into a paste by adding water, 

 prepared a little at a time and only as fast as 

 needed." 



"I 've seen them do it," Emile interposed; "the 

 workman takes a few handfuls of that powder out 

 of a bag, and then he mixes it with a little water in 

 his trough with a trowel. He scrapes the paste all 

 together in his hand and uses it immediately, before 

 making any more. Why don 't they mix all the plas- 

 ter at once, as they do with lime when they make 

 mortar ? ' ' 



"Plaster is not all prepared beforehand for the 

 reason that it hardens very quickly, turns to stone, 

 and is then unfit for use. Accordingly, to have it 

 in a suitable state of softness, it must be prepared 

 at the moment of using. " 



"And what do they make that powder of that 

 turns to stone when it is mixed with water?" 



"Plaster is made from a stone called gypsum, 

 which, always the same as to its nature, varies much 



56 



