MORTAR-MAKING. 899 



Sand is o-enerall}^ mixed with lime, however, for the sake 

 of both economy and strenj^^th, and for ordinary purposes 

 any <2,ood Hnie will stand tiie admixture without its properties 

 being- seriously impaired. It remains to be considered how 

 much sand may be thus safely used, and what kinds of sand 

 are the best. 



Theoretically the best wall is that in which the cementing 

 material is just as strong- as the brick or stone cemented. There 

 is evidently no object in having the cement stronger ; but up 

 to the point of equal i-esistance the strength of the whole 

 wall will vary with that of the cement. One writer on this 

 subject says : — " In the case of fat lime the strongest mortar 

 that can be made with it bears such a very small proportion 

 to the strength of a ])rick, that it matters comparatively little 

 what prQ))ortion of sand is used with it. If there is much 

 saving effected in price, three of sand may be used to one of 

 lime, and the resistance of the mortar formed would only 

 descend to ^y of that of the brick. But (as has been said 

 liefore) such a mortar should never be used at all. AVith 

 feebly hydraulic limes 2i cubic feet of sand may be mixed 

 with one cubic foot of lime, and the result will be a mortar of 

 I or \ the resistance of brick. With hydraulic lime of good 

 quality 1|^ to two parts of sand may be used to one part of 

 lime, but this is the limit. For hydraulic works and foun- 

 dations equal portions of lime and sand should be the limit 

 allowed," 



Opinions differ considerably as to what sand is best suited 

 for mixing- with lime, Vicat concluded that the advantage 

 of the three different descriptions of sand employed by him 

 varied with the nature of the lime. 



He calls coarse sand those whose grains, supposing them 

 round, vary from ^ to ^ of an inch in diameter; fine sand, 

 whe)'e the graius vary from J-^ to ^\ of an inch in diameter ; 

 and according to this statement ranked their superiority with 

 limes as follows : — 



1st. 2nd. 3rd. 



For eminently hydraulic limes Fine Mixed Coarse. 



For slightly „ ,, Mixed Fine Coarse. 



For fat limes ,, „ Coarse Mixed Fine. 



Powder, especially when derived from calcareous sub- 

 stances, will be found to make excellent mortar both with 

 hydraulic and eminently hydraulic lime. lie considered that 

 the greatest difference in the hardness of mortars of fat limes, 



