Plastering. (A.) In making mortar for plastering, it is always wise to purchase some well-known make of lime, as it varies in quality and strength; but it is usually safe to allow 3 bushels of sand to one of lime and 2/3 of a pound of hair.

Sand for plastering should be coarse, sharp, and clean; that taken from a river bed may be clean, but usually it is not sharp, though it is often used for mortar where none other is obtainable.

To test sand for clay or loam, put it in a glass of water. After being stirred, the sand will settle to the bottom, and the loam and clay, if present, will settle upon it. Another way is to squeeze a little damp sand in the hand; if it is free from clay or loam, it will fall apart as soon as the hand is opened.

If in doubt as to whether or not the sand is sharp enough, examine it with a microscope: if the corners of the grains are rounded, and the surface smooth and glassy, the sand should not be used.

Hair should not be put in the mortar until the lime has thoroughly slaked, as the heat will destroy it.

Either cow's or goat's hair is the kind generally used, the latter being preferred, as it is longer, finer, and mixes better. Manila and wood fiber are used to some extent as a substitute for hair, it being claimed that they are not affected by heat from imperfectly slaked lime.

It is a good plan to allow the mortar to stand a few days before it is used, as the quality of it is much improved, and there will be no small lumps left unslaked, which often happens in mortar which has been made too hurriedly.

(B.) The plastering upon the best buildings is usually three-coat work.

The first, or scratch coat, consists of a layer of mortar 1/4' in thickness, spread evenly over the laths, and well pressed between them to form a clinch. The durability of the work depends to a great extent upon the strength of this clinch, so care should be used to make it effective. After the scratch coat has hardened from two to four days, it is scratched so that it will form a good key for the next coat, though some plasterers sweep the wall with a coarse broom while this coat is moist.

The scratch coat should be nearly dry, so that it will be stiff enough for the second or brown coat to key well into the scratches, and at the same time not so dry that the brown coat will not unite to it. If it is too dry, it should be dampened. After the brown coat is hard, but not thoroughly dry, it is ready for the skim, or putty coat, which is made of a thin coat of lime and plaster of Paris, and worked down very carefully to a smooth, hard finish. If the skim coat is not well put on, or if the plastering underneath is improperly dried, small cracks probably will appear upon the wall.

There are several methods of doing the different parts of the work, but the above is the method generally followed.

Upon work where economy is necessary, quite satisfactory results are obtained by two-coat work, in which the first coat is left in nearly the shape of the second coat, as above described; after drying sufficiently, the finishing coat is laid directly upon it, being a little thicker than the skim coat of three-coat work. This method is not recommended where the best results are desired, as the skim coat is apt to crack or peel off.

Generally it is the carpenter's place to close in for the plasterer, by which is meant the closing of all openings to keep out cold and drafts which would cause freezing or uneven drying. Many builders plan to have the window sashes in place before the plasterers begin their work, especially in the winter time, but in general it is the custom to make rough frames and to cover them with a cheap cotton cloth, which allows the light to pass through, but keeps out the drafts. If the air is very dry and warm, this is sometimes as necessary as it is to keep out the cold in winter, for if plaster dries too rapidly, it will crack badly; the surface should not dry faster than the back. When it is necessary to have fire to assist in drying out plaster, or to keep it from freezing, it is generally the plasterer's place to maintain it. In many parts of the country, it is rarely necessary to use these precautions, but in parts where there is danger of the plaster freezing, or of drying too rapidly or unevenly, all reasonable precautions should be taken.

There are a number of different makes of prepared plaster upon the market, which are fast gaining the favor of architects, as they are lighter than lime mortar, more easily applied, dry more quickly, are less apt to freeze, and are not so liable to crack after the wall is finished, and when the building seasons. There is little doubt that ultimately they will be used almost universally, as they are now specified upon the best work.