On Water Cements. 
71 
1831.] 
two extremes, spoils the cement. It was before observed, that the proportion of 
the protoxide of iron may vary in a still greater degree. In short, the above 
ingredients, which are the most proper for forming an efficient artificial water 
cement, do not combine in absolutely definite proportions, although there are cer- 
tain limits that cannot be passed without failure. 
38. The carbonate of magnesia alone may be added previously to calcination, 
to any artificial cement mixture, or to any of the natural cement stones, both 
being pulverized, in any quantity, or to any given excess, without spoiling them, 
it being, as was before observed, an efficient water cement in itself 2 . 
39. In those countries, in which none but very hard lime stone is to be had, an 
artificial cement may be formed, by using a mixture of clay and of calcined lime, 
that has been long and thoroughly slaked, in the usual proportions, instead of 
pulverizing the lime stone itself. 
40. Our experiments at Chatham have also proved, that a mixture of quick lime, 
with calcined and pulverized clay, forms a very inferior cement, although it has 
occasionally been used for that purpose, since the time of the Romans. In order 
to succeed properly, all the ingredients for an artificial water cement, must be 
mixed previously to calcination, not afterwards. 
§ g , — Of the Practical Purposes to which Water Cements are applied. 
41. First, instead of mortar for wharf walls, docks, &c., and more especially for 
the facings of such walls, as it is not deemed necessary to use cement throughout 
their whole thickness. 
42. Secondly, for arches over doors and windows, and for bond courses in the 
walls of buildings. 
By using cement for such arches, the thrust upon the piers and abutments is 
done away : also, by using cement instead of common mortar, in three or four suc- 
cessive courses of brick work, in the walls of a building, in one or two parts of 
each story, a beneficial bond is obtained. 
43. Thirdly, as stucco for the external walls of buildings, in which case it is 
generally applied about three quarters of an inch in thickness, and is finished by 
floating. 
44. For all of the above purposes, the cement is almost always mixed with 
clean sharp sand, in equal quantities. The addition of a great proportion of sand 
makes the mixture too gritty, and prevents it from setting so well as it ought to do. 
45. Fourthly, for the lining of tanks, or for the covering of casemates. 
For these purposes, the cement is generally applied about three quarters of an 
inch thick, but it is always used pure, instead of mixing it with sand. In all cases, 
it is usual to apply it in two successive coats, of about three-eighths of an inch in 
thickness ; and in tanks or casemates, each of those coats must be well worked in 
by the trowel, not by floating. The surface of the first is left rough or uneven : 
the second or external coat, on the contrary, cannot be made too smooth. 
46. The second coat should be laid on before the first is quite set, and therefore 
one plasterer should apply the first, followed by another plasterer, who should be 
in readiness to apply the second as soon as possible. Hence, these two coats are 
virtually one, and may be considered as such. Stucco or plastering in cement is 
s A calcined mixture of chalk, pipe clay, and the carbonate of magnesia, which 
forms the handsomest of all the artificial cements made by us at Chatham, promises 
fairer to become a substitute for the German lithographic stone, than any substance 
I know. It is my intention to prosecute this research, but I am not sanguine as to 
final success. 
