Density of Mortar

Where large quantities of mortar are required, as in the construction of a large masonry dam, an automatic-measuring and mortar-mixing machine is sometimes used.* Mortar mixers are somewhat similar to concrete mixers (see § 340-41), but are only occasionally required, and are likely to be used less frequently in the future than in the past owing to the substitution of concrete instead of masonry; and hence nothing more will be said here concerning mortar-mixing machines.

GRouT.

This is a thin or liquid mortar of lime or cement. The interior of a wall is sometimes laid up dry; and grout is poured on top of the wall and is expected to find its way downwards and fill all voids, thus making a solid mass of the wall. Grout should never be used when it can be avoided. If made thin, it is porous and weak; and if made thick, it fills only the upper portions of the wall. To get the greatest strength, the mortar should have only enough water to make a stiff paste.

The following will he found useful in estimating the amounts of the different ingredients necessary to produce any required quantity of mortar: Portland Cement. In this country portland cement now weighs 376 pounds net per barrel, and is usually shipped in bags weighing 94 pounds net, of which four make a barrel. The capacity of an American cement barrel, which is generally a little greater than that of a foreign one, varies from 3.50 to 3.70, the average being

3.61 cu. ft. A barrel of portland cement will make from 1.2 to 1.4 barrels measured loose.

The quantity of paste produced from a given quantity of cement depends upon the amount of water used, and also upon the thor oughness of mixing and the degree of tamping. In a general way the dryer the mortar the greater the volume; and the less thorough the mixing or the less the tamping, the greater the volume. From 100 to 105 pounds of cement and from 29 to 31 pounds of water will make a cubic foot of paste having about the plasticity used by masons, which is considerably wetter than the standard consistency employed in laboratory tests of cements. Occasionally a cement is found of which only 95 pounds are required to make a cubic foot of paste.

Natural Cement.

Formerly Rosendale natural cement weighed 300 pounds net per barrel, and the product of western mills 265 pounds net; but recently most of the manufacturers of natural cement have agreed upon a uniform weight of 2S2 pounds net per barrel, and also agreed upon three bags of 94 pounds each to the barrel. A barrel of natural cement will make from 1.33 to 1.50 barrels if measured loose.

Volume for volume, natural cement will make about the same amount of paste as portland; that is, 75 to 80 pounds of natural cement and about 0.45 cu. ft. of water will make a cubic foot of plastic paste.