This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Of late years many varieties of metal lath have been placed upon the market. The use of such lath is generally required on boiler-room ceilings, and in other places exposed to strong artificial heat. Many varieties of metal lath - including all those made of wire - require supports at closer intervals than is provided by the studding, nine inches being generally considered the best distance. This necessitates either a closer spacing of studs than is otherwise necessary or desirable, or a series of furrings fastened to the wall studding.
There are some metal laths - generally those made on the expanded principle - that are sufficiently stiff, in one direction, to allow of a spacing of supports greater than nine inches; but, for ordinary wire cloth, no wider distance should ever be allowed, unless the cloth is itself artificially stiffened. All metal lath should be securely fastened by staples, and stretched before nailing, to increase its stiffness as much as possible.
In using metal lath, care should be taken to prevent plaster cracks along the line of jointure. The use of metal lath also requires three coats of plaster, in order to stiffen the lath sufficiently to resist the pressure required to finish the last coat.
Lathing and plastering are generally estimated, and the various materials are all figured, by the square yard. In small work, no openings are deducted unless they exceed sixty square feet in area. In figuring up plaster by quantity, when openings are allowed for, it is sometimes customary to add half of the contents when measuring closets; while small triangular wall pieces are figured as though square, in order to make up for the extra amount of labor required in plastering such restricted or odd-sized surfaces.
Several makes of plaster board are in the market and being extensively advertised. They come in eight inch wide boards or large sheets of 32 by 36 inches, and are nailed directly upon the wall framing. One coat of plaster - in three-coat work - may then be dispensed with. These boards save time, being rapidly set in place even by unskilled carpenters,and the plaster itself drys out much more rapidly. They are, however, frequently the cause of cracks that appear in the finished plaster where the edges of the boards come together - sometimes even after the wall has been papered.