58 FOUNDATIONS EXPOSED, PERAK MUSEUM. 



England, however, beds similar to the ones here would be 

 crowded with bones and shells, as all will know who have 

 ever done any geological work there. 



The conclusions to be di-a'wm from these foundations are 

 that all concrete used below the water line should be made with 

 hydraulic lime, which will set at once and which when set will 

 be much more insoluble than pure carbonate of lime ; also that 

 in some cases the subsidence of a building is due to the 

 foundations rhemselves and not to the soil on which they are 

 laid. 



The condition of the walls above the foundations is in a 

 great measure due to the Chinese method of Ijuildmg. The 

 mortar is generally mixed as it is wanted, and there is usually 

 too much lime in it. It is brought in buckets to the bricklayer, 

 who spreads it out on the top of the last layer of bricks. He 

 then takes dry bricks and arranges them on top of the mortar 

 for the next com-se, spreads another layer of mortar on top of 

 them, and so on. The great points, according to a Chinese brick- 

 layer, are to have dry bricks and the mortar of such a consistency 

 that when it is used the bricks will absorb all the surplus 

 moisture from it and render it fairly hard ab once. Then as 

 soon as the wall is built it is coated inside and out with a thick 

 layer, of lime plaster. The Chinese method takes no account of 

 the requirements of the case. These may be l)riefly stated to be 

 that the proportion of lime to sand should lie such that it fills 

 with a very thin film the spaces between the grains of sand. 

 Everything beyond this weakens the mortar, for sand is much 

 stronger than carbonate of lime, and the more lime the greater 

 amount of carbonic acid is necessary to set the mortar. The 

 lime shoidd be slacked and mixed with the sand as soon as it 

 comes from the kiln, and should not be used for a long time 

 after it is made. The bricks should be used wet, and the mortar 

 put under and round each individually. A very considerable 

 time should be allowed to elapse before walls are plastered, so as 

 to allow the moi-far of the wall itself to have time to set before 

 the supply of carbonic acid is cut off by the lime of the plaster, 

 and the wall should be well wetted before being plastered so as 

 to keep it damp for some considerable time after it is laid. 



The setting of mortar is a chemical process depending on 

 carbonic acid gas permeating the wall and combining with the 

 lime to form a crystalline carbonate. For the success of the 

 reaction it is essential that the lime is wet, otherwise, although it 

 will become carbonised, it will not crystallise, and it is the crystal- 

 lization which constitutes setting. Dry lime exposed to air does 

 not harden, but remains a soft powder, though it soon changes 



