214 Oil Concrete as a Building Material for 



\a fine powder, in which state it may be secured in casks or bags 

 for transit or storage. Where machinery cannot be had, it will 

 answer the purpose if it is air slaked, or, to make this operation 

 quicker, water may be thrown upon the lime, thus producing the 

 characteristic flour. In both of the two latter methods care must 

 be taken that every particle of lime be slaked. To ensure this the 

 lime should be passed through a fine sieve, and the residue gone 

 over again. If lumps of unslaked lime are incorporated in the 

 concrete, its stability and strength will be greatly reduced by 

 the portions of unslaked lime bursting, which may not take 

 place until the walls are completed, thus causing a great deal of 

 damage. The effect would be similar, in fact, to that of a lump 

 of lime bursting in a brick. 



Lime concrete for walls above ground is not to be compared 

 to cement concrete ; of course it is cheaper than the latter, and 

 good enough for foundations below ground, or even in walls of 

 a bulky nature, such as retaining and breast walls. 



Cement. — Cement for making concrete is of two kinds, the 

 natural, or " Roman," and the artificial, or " Portland." Both 

 are hydraulic, and of very simple manufacture, the former being 

 made out of the natural cement stone found in many parts ol 

 the country, and the latter being a mixture of lime and clay. 

 Both may be burnt in a common open lime-kiln ; they are 

 ground to powder and stored awiay in casks or bags, as pre- 

 viously mentioned for lime. Before the recent advance in the 

 price of coal and labour, Roman and Portland cement could be 

 bought at from 30^. to 355. per ton ; now the price is from 40^. 

 to 45s. 



Great care should be exercised in procuring cement for 

 concrete ; its quality should always be guaranteed by the manu- 

 facturer as up to a certain standard of excellence ; a register of 

 the strength of each sample sent out is generally kept by the 

 manufacturer. 



Owing to the great experience in the manufacture of " Port- 

 land " cement, and the methods adopted for testing it, there can 

 be no doubt that it is now superior to the natural, or " Romanr 

 A great deal has been written upon limes and cements, and 

 many valuable and costly experiments have been made, espe- 

 ■ cially by Major-General Pasley ; yet there is still scope for a 

 great deal more with respect to these important building 

 materials. 



Twenty-five years ago I spent the greater part of a year in 

 experimenting upon these materials, and, after numerous trials 

 to produce a good water cement, I could not beat in quality, 

 much less in price, the Portland cement made on the banks of 

 the Medway from the chalk and blue clay of that locality. 



