TESTS OF WISCONSIN BUILDING STONE 537 



The walls of a building constructed out of a porous stone 

 are seldom completely saturated with Water, although they may 

 be wetted by the water of imbibition which adheres as a film to 

 the individual grains and is thus conducted through the body of 

 the wall. If a stone with pores of capillary size should be satu- 

 rated in any part with water and the supply be discontinued the 

 interstatial water would be very quickly drawn off at the surface 

 or at the base of the wall through capillarity. It rarely hap- 

 pens that atmospheric conditions are such that a stone with 

 capillary pores can become saturated with water and freeze 

 before the water is sufficiently dissipated to prevent injury. 



Rocks in which the grains are closely compacted, without 

 respect to size, will have a small percentage of pore space and 

 also pores of very small size. Many of the pore spaces of the 

 granite and limestone are certainly of not greater than sub- 

 capillary size. Water is taken up and given off by a rock hav- 

 ing pores of this size much more slowly than by one in which 

 the pores are of capillary dimensions. When the sub-capillary 

 pores of a rock contain water in any quantity they should be 

 theoretically filled. The sub-capillary pores near the exposed 

 surface of a stone wall may be filled by long-continued rains, 

 although the water may never penetrate to any considerable 

 depth. If such a period of weather is followed by freezing con- 

 ditions a stone in which the pores are of sub-capillary size will 

 be in greater danger than one having pores of capillary size. It 

 should be remembered that stone is damaged by freezing only 

 when the pores are over nine tenths filled with water. 



A wall built out of granite or other stone in which the 

 porosity may be very low, but the pores of sub-capillary size, is 

 in as great danger from alternate freezing and thawing as a wall 

 built out of sandstone or other rock in which the porosity is 15 

 or 1 8 per cent., but in which the pores are of capillary size. It must 

 be understood that this does not apply to laminated, bedded, or 

 shaly stone, between the layers of which the water may collect 

 more rapidly than it can be carried off through the pores. 

 Water which is thus collected along bedding or other parting 



