Mortar for a second coat on lath may be of about this same consistency of mixture. For the final coat (the putty coat or hard finish) but very little sand is used. The harder the finish, the less the amount of sand. For this coat, the sand is mixed at the time when the putty is run off. For hard finish, when marble dust, brick dust, or anything of that sort is added, it is generally mixed together on the mortar-board immediately before applying. Stucco, or plaster of Paris, is never mixed with putty until immediately before using, on account of its rapid setting, which occurs in a few moments after mixing. When once set before being applied, it becomes useless. No more water than is necessary should be added, either in the mix ing of the mortar at first or in its subsequent tempering, as over-much wetting of the lime deprives it of a considerable proportion of its strength, and also retards the setting process by giving that much more moisture that is necessary to be disposed of by evaporation or crystalli zation.
A bushel of lime is standardized to weigh 80 pounds; 200 pounds is allowed to the barrel; a bushel contains about one and one-quarter cubic feet. A barrel of sand is supposed to contain 3 cubic feet of sand, and a bushel of sand weighs about 120 pounds, and wet mortar 130 or 132 pounds. When hard, mortar is figured to weigh about 110 pounds to the cubic foot.
To summarize—one barrel of lime, 200 pounds, will take about a cubic yard of sand. In most localities a load of sand is supposed to contain twenty-seven cubic feet, or a cubic yard; but it is frequently less than this, extending down to two-thirds of the amount. To the
barrel of lime should also be used about two barrels of water and—as we have seen—upwards of two bushels of hair for a first coat. Hair comes in paper bags weighing generally something under eight pounds and containing enough hair to beat up into a measured bushel. This amount of material, when the lime has been slaked and the whole mixed together, will amount to 35 or 40 yards (about 5 barrels) of mortar; and the amount should cover about 40 square yards of lathed area, requiring about 600 laths to surface.
The final skim coat is mixed roughly to the following proportions: A cask of lime to a half-tub of water, which should take up about a barrel of the hard, clean sand used in the surface coat. Generally the plasterer uses a larger barrel or hogshead for water, than the cask in which the lime is delivered. Also, in some localities, the lime will run somewhat more than 200 pounds to the barrel, Maine lime from Rockland being supposed to average 220 pounds. Rockland lime is considered in the East good lime for scratch and brown coats, but many masons prefer Jacob's lime for the finish coat.
It should be remembered that the bulk of the completed mortar mixture does not equal the total combined bulk of its various ingre dients, but is less than the aggregate bulk by about one-quarter.