338 Mr. J. Napier on Damp Walls. 



are likely to produce damp. Wood, no doubt, forms an important item 

 in the building of a house, but wood is generally seasoned before being 

 put into a building, so that, of itself, it is not a source of damp. Never- 

 theless, new wood absorbs moisture rapidly, either from a damp atmo- 

 sphere, or when in contact with wet substances ; so that the wood about 

 a house, from contact with damp, very soon becomes a source of mois- 

 ture in newly-built houses, and that it is no mean source of supply by 

 increasing the evaporating surface, will be evident when I mention that 

 it will absorb from a damp wall fifteen per cent, of its whole weight of 

 water, and give it out very easily by evaporation or contact, as may be 

 amply verified in wall presses of newly- built or otherwise damp houses. 



We have now to consider the general question of damp walls, both in 

 new and old houses ; and, being guided by the data obtained, let us first 

 consider the state of a new house finished for a tenant, both those built 

 for the labouring classes and for the middle classes. 



The stones naturally contain, on an average, 1;^ gallon per cubic foot. 

 They never lose all this water, retaining about ^ even under the most 

 favourable circumstances for drying. The quantity they lose the first 

 year varies according to these circumstances ; but under the most favour- 

 able conditions, and where there was good ventilation, according to one 

 experiment, the loss amounted to fully half a gallon per cubic foot. 



The bricks used for partitions, although not wet of themselves, become 

 saturated by the mortar and plaster put upon them, and therefore may 

 be said to contain 1| gallon per cubic foot. 



The plaster in a condition fit to work I have found by several trials 

 to be by weight — 



45 sand, 



5 lime, 



50 water, 



so that one hod of this contains about 5 gallons water, which go over but 

 a small surface of wall, being sufficient to supply either brick or stones not 

 previously saturated. After a few weeks in dry weather the plaster 

 hardens and seems to sweat, probably from taking up carbonic acid. 

 When the excess of this sweating is evaporated, and the plaster perfectly 

 hard, the house is, in general, ready to be occupied, more especially 

 those for the working classes. I have often seen such houses tenanted 

 before this, and before the plaster had properly hardened, and when 

 it could not contain less than 20 to 30 per cent, of water — a prac- 

 tice most reprehensive, and against which the law should be enforced 

 upon landlords. Workmen's houses have no lining or battening, but are 

 plastered upon the stone walls, so that when they are considered fit for 

 occupation the walls must contain about IJ gallon per cubic foot. 

 So that if we take a room 12 feet square and 10 high, and if only 



