Lath
Lath seen from the back with brown coat oozing through
Traditionally, plaster was laid onto laths, rather than
plasterboard as is more commonplace nowadays.
Wooden laths are narrow strips of straight-grained wood
depending on availability of species in lengths of from two to four or five
feet to suit the distances at which the timbers of a floor or partition are
set. Laths are about an inch wide, and are made in three thicknesses; single (⅛
to 3⁄16 inch thick), lath and a half (¼ inch thick), and double (⅜–½ inch
thick).
The thicker laths should be used in ceilings, to stand the
extra strain (sometimes they were doubled for extra strength), and the thinner
variety in vertical work such as partitions, except where the latter will be
subjected to rough usage, in which case thicker laths become necessary. Laths
are usually nailed with a space of about ⅜ of an inch between them to form a
key for the plaster.
Laths were formerly all made by hand. Most are now made by
machinery and are known as sawn laths, those made by hand being called rent or
riven laths. Rent laths give the best results, as they split in a line with the
grain of the wood, and are stronger and not so liable to twist as machine-made
laths, some of the fibers of which are usually cut in the process of sawing.
Laths must be nailed so as to break joint in bays three or
four feet wide with ends butted one against the other. By breaking the joints
of the lathing in this way, the tendency for the plaster to crack along the
line of joints is diminished and a better key is obtained. Every lath should be
nailed at each end and wherever it crosses a joist or stud. All timbers over
three inches (76 mm) wide should be counter-lathed, that is, have a fillet or
double lath nailed along the centre upon which the laths are then nailed. This
is done to preserve a good key for the plaster.
Walls liable to damp are sometimes battened and lathed to
form an air cavity between the damp wall and the plastering.
Lathing in metal, either in wire or in the form of
perforated galvanised sheets, is now extensively used on account of its
fireproof and lasting quality. There are many kinds of this material in
different designs, the best known in England
being the Jhilmil, the Bostwick, Lathing, and Expanded Metal lathing. The two
last-named are also widely used in America.
Lathing nails are usually of iron, cut, wrought or cast, and
in the better class of work they are galvanized to prevent rusting. Zinc nails
are sometimes used, but are costly.
