UO Mr. J. Napier on Da^np Walls. 



of this kiud of damp walls. I have been informed of a mixture of 

 lime with oxide of iron, and a certain kind of ashes ground, which soon 

 hardens so as to become impervious to moisture, I have not seen the 

 mixture, nor houses where it was used, but, if effective, it is to be 

 regretted that it is not more generally employed. 



Damp also penetrates through the side walls of a house, from the 

 thinness of the wall and the porous nature of the stone. I have several 

 times witnessed this on the second floor of a three and four storey house 

 so great as to loosen the paper and be visible upon the plaster inside, and 

 to appear in every continuance of wet weather. I believe that this is a very 

 prevalent source of damp in houses exposed to the weather, although it 

 may not be so great as to attract notice. Now prevention from this 

 source could be effected cheaply and easily. I have seen houses on the 

 coast tastefully painted over by a sort of pitch and tar, and have often 

 considered it a lesson that might be applied beneficially to the outside of 

 oui- porous walls, and any colour could be given to such cheap matters 

 as would throw off and resist the wet penetrating the stone or brick. 



Houses under the level of the ground, and especially where the ground 

 abuts upon the wall, are never dry, and should never be inhabited by 

 any person, and especially never used as sleeping apartments. 



There is another cause of damp on walls, which affects a certain class 

 of houses very much, such as those having bare walls. This is caused 

 by sudden changes of temperature, and moisture in the aii\ When the 

 temperature has been cold for some time, and suddenly becomes warm, 

 the plaster and stone being bad conductors of heat, remain for a long 

 time much colder than the atmosphere. The consequence is, a conden- 

 sation of the watery vapour of the air, and in great quantities, for the 

 condensation sets up a current of air towards the wall, and the water so 

 condensed is often very considerable. If the walls be of non or slow 

 absorbent materials, the moisture collects and runs down in drops, and 

 attracts notice, and should be removed by a cloth or sponge. Lime- 

 stone walls are very subject to this from their slow absorbent property ; 

 hence people get an impression that limestones are more liable to damp 

 than sandstone, while of all kinds of damp this is the least to be dreaded, it 

 being easily removed. Lighting a fire in a room upon a cold day will pro- 

 duce the same effect upon such walls, and give rise to the common notion 

 that the fire is drawing out the damp. The same condensation takes place 

 upon plaster and sandstone walls, but the moisture is absorbed and does 

 not become visible. We have seen a dry plaster under these circum- 

 stances become saturated with moisture, and penetrating to the depth of 

 two inches, and the room being damp in consequence for weeks after, and 

 this is a condition and result always occurring, especially in spring-time 

 and harvest. Papered walls are affected in the same way, but probably 

 not to the same extent ; but this damp imbibed and retained in a room 



