Mr. J. Napier on Damp Walls. 337 



from I to 2 gallons per cubic foot ; and these experiments were made with 

 what are termed good outside bricks, there being often used in building 

 partitions, soft, coarse bricks, which imbibe water like a sponge. In some 

 trials the water passed up the whole length of a brick by capillary attraction 

 in eight hours ; in other bricks it took twenty hours, which may be stated 

 as the two extremes. The absorption and ascension of the water in well 

 burned and partially glazed bricks, was often confined to one or two faces 

 of the brick that had escaped the glazing ; so that, if means could be 

 adopted to partially glaze the whole surface of the brick, the absorbent 

 property would be removed. The application of a glaze to bricks I am 

 afraid would not do, the low heat at which it would require to fuse would 

 render such glaze liable to decompose in the air. Bricks, from the poverty 

 of the clay used, fuse at a low heat, so that I think a different mode of 

 baking or firing so as to produce the partial fusion over tlie whole surface 

 of the brick that is now confined only to one or two faces, would do much 

 to improve the quality of brick, so far as the protection from damp 

 is concerned, although it would be against their binding by lime, as a cer- 

 tain amount of absorption is necessary for this purpose. 



Plaster or Moetae. 



The next substance to be considered is plaster. If a little plaster be 

 taken after hardening and drying, and put into water, or if water is 

 allowed to drop upon it till saturated, it takes up fully two gallons per 

 cubic foot. Its capillary attraction is very rapid for two or three inches 

 after which it becomes slower than the average of brick or sandstone. 

 It gives out any excess of water easily when brought into contact with 

 other absorbents in a drier state, thus evaporating and communicating 

 moisture freely to everything around it. Plaster, however, must be 

 considered in its different ingredients, hme, sand, and water, all of which 

 play important parts in damp walls. 



Lime used for mortar differs altogether from the limestones used in 

 building, having been subjected to the operation of burning, where its 

 property is altogether changed, and then to slacking, when it absorbs or 

 combines with from one-third to one-half of its weight of water. If the 

 limestone has contained any acid or alkaline salt, which is often the case, 

 these are affected by the heat and slacking. If the water contains any 

 salts or acids, which is universally the case, then there will be formed in 

 the mortar ingredients subject to decomposition, and also, which is not 

 uncommon, the sand mixed with the lime contains matters subject to 

 decompose, such as common salt or organic matter, all of which in a 

 short time become a soui'ce of perpetual annoyance, showing itself either 

 in the form of damp or efflorescence upon the plaster, which I will notice 

 presently. Such, then, are the principal materials of our walls, which 



