TABLE Showing the relative Breaking Weights in lbs. of Briquettes having a sectional area at the neck of two and a quarter square inches.

Nature of Lime or Cement.

Age in

Days when fractured.

Composition of Mortar.

Remarks.

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 .

167

206

149

113.5

..

White chalk lime .

164

67.5

..

..

..

..

Do. (Selenitic) .

161

63

58

78

72.3

..

Burham lime (Selenitic)

165

...

...

170

210

Good Med way grey lime, sold by Messrs. Lee.

Do. do.

234

• ••

340

..

..

Do. do.

161

255

..

..

250

Halkin lime (Selenitic)

76

128.5

197

99

111

Good hydraulic lime.

Dolgoch lime (Selenitic)

62

155

156.5

157

206.5

Very hydraulic lime.

Mixture Of Lime And Cement

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."

Portland Cement Mortar With Large Proportion Of Sand

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.

Grout is a very thin liquid mortar sometimes poured over courses of masonry or brickwork in order that it may penetrate into empty joints left in consequence of bad workmanship.

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.

Precautions In Using Mortar

Fat lime mortars, unless improved by adding pozzuolana and similar substances, are so wanting in strength that any precautions in using them are of but little avail.

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.

In frosty weather the freezing and expansion of the water in the mortar disintegrates it and destroys any work in which it may be laid.

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.