Days when fractured.
Composition of Mortar.
3 sand to l cement or lime.
4 sand to 1 cement or lime.
5 sand to l cement or lime
6 sand to l cement or lime.
Breaking Tensile Stress on 21/4 Square Inches.
Portland cement .
White chalk lime .
Do. (Selenitic) .
Burham lime (Selenitic)
Good Med way grey lime, sold by Messrs. Lee.
Halkin lime (Selenitic)
Good hydraulic lime.
Dolgoch lime (Selenitic)
Very hydraulic lime.
Bad lime is much improved by mixing Portland cement with it.
General Gilmore says : - "Lime paste may be added to a cement paste in much larger quantities than is usually practised in important works without any considerable loss of tensile strength or hardness.
"There is no material diminution of strength until the volume of lime paste becomes nearly equal to that of the cement paste, and it may be used within that limit without apprehension under the most unfavourable circumstances in which mortars can be placed."
Mortar composed of 1 Portland cement, 8 sand, and 1 of slaked fat lime is much better and generally cheaper than 1 of grey lime to 2 sand - the slaked lime slightly weakens the mortar, but is necessary to prevent it from working "short." Loam is sometimes used instead of the slaked lime, but it weakens the mortar still more. This mortar is greatly preferable to that made from lime when frost is to be feared.
The following was used in the outer wall of the Albert Hall: -
1 Portland cement. 1 grey lime (Burham). 6 clean pit sand.
The lime was slaked for twenty-four hours, then mixed with sand for ten minutes. The cement was then added, and the whole ground for one minute. Such a mixture must be used at once.
It may also be necessary in deep and narrow joints between large stones.
It is deficient in strength, and should not be used where it can be avoided.
In using hydraulic limes and cements it should be remembered that the presence of moisture favours the continuance of the formation of the silicates, etc., commenced in the kiln, and that the setting action of mortars so composed is prematurely stopped if they are allowed to dry too quickly.
It is, therefore, of the utmost importance, especially in hot weather, that the bricks or stones to be imbedded in the mortar should be thoroughly soaked, so that they cannot absorb the moisture from the mortar; and also in order to remove the dust on their surfaces, which would otherwise prevent the mortar from adhering.
Mortar should be used as stiff as it can be spread; the joints should be all well filled; grout should never be used except with large blocks or in other cases where from the position or form of the joint it cannot be filled by mortar of proper consistency.
Mortar should always be placed for the use of the builder on a small platform or "banker," or in a tub, to keep it from the dirt.
Cement mortars have, of course, peculiarities depending upon the nature of the different cements. These have been noticed in treating of those substances.