THE ACTION OF FROST IN WATER-PIPES. 305 



The mortar most liable to suffer is that which is porous 

 and pulverulent within, but has been cleverly faced or 

 pointed with a crust of more compact material. This 

 outer film prevents the exuding of the expanding ice crys- 

 tals, is thrust forth bodily, and retained by ice-cement 

 during the frost, but it falls in scales when this temporary 

 binding material thaws. Mortar that is compact through- 

 out does not suffer to any appreciable extent. This is 

 proved by the condition of the remains of Roman brick- 

 work that still exist in Britain and other parts of Europe. 

 Some of the old shingle walls at Brighton and other parts 

 of the south coast, where the chalk for lime-burning was 

 at the builder's feet, and where his mortar is so thickly 

 laid between the irregular masses of flint, also show the 

 possible duration of good mortar. The jerry builder's 

 mortar, made of the riddlings of burnt clay ballast and 

 dust-hole refuse just flavored with lime, crumbles imme- 

 diately, because these materials do not combine with the 

 lime as fine siliceous sand gradually does, to form an im- 

 permeable glassy silicate. 



Stucco is punished by two distinct modes of action. 

 The first is where the surface is porous, and the water per- 

 meates accordingly and freezes. This, of course, produces 

 superficial crumbling, which should not occur at all upon 

 good material protected by suitable paint. The other case, 

 very deplorable in many instances, is where the water finds 

 a space between the inner surface of the stucco and the 

 outer surface of the material upon which it is laid. This 

 water, when frozen, of course, expands, and wedges away 

 the stucco bodily, causing it to come down in masses at the 

 thaw. This, however, only occurs after severe frosts, as 

 the ordinary mild frosts of our favored climate seldom en- 

 dure long enough to penetrate to any notable depth of so 

 bad a conductor as stone or stucco. It is worthy of note 

 that water is a still worse conductor than stone. 



Building stones are so various both in chemical composi- 

 tion and mechanical structure that the action of freezing 

 water is necessarily as varied as the nature of the material. 

 The highly siliceous granites (or, rather, porphyries that 

 commonly bear the name of granite) are practically imper* 



