206 CHAPTER SIXTEEN
Gypsum Plaster Lath. In sheet form, gypsum plaster
lath provides a rigid base for the application of gypsum plas-
ters. Special gypsum cores are faced with multilayered lami-
nated paper. The different lath types available are plain
gypsum, perforated gypsum, fire-resistant, insulating, and
radiant heat. Depending on the supporting construction, the
lath may be nailed, stapled, or glued. The type of spacing of
the attachments depends on the type of construction and
the thickness of the lath. Gypsum lath may be attached to the
supporting construction by the use of nails, screws, staples,
or clips.
Plain gypsum lath is available in thicknesses of 3/8 and
1/2 inch with a face size of 16 48 inches. The 3/8-inch
thickness is also available in 16 96-inch sizes. (A 16 3/16-
inch width is available in certain areas only.) When the plas-
ter is applied to this base, a chemical bond holds the base to
the gypsum lath. Gypsum lath 24 144 inches is also avail-
able in certain areas.
Perforated gypsum lath is available in a 3/8 inch
thickness with a face size of 16 48 inches. Holes 3/4
inches in diameter are punched in the lath spaced 16
inches on center. The perforated lath permits higher fire
ratings, because the plaster is held by mechanical as well as
chemical bonding.
Fire-resistant gypsum lath has a specially formulated
core of special mineral materials. It has no holes, but it pro-
vides additional resistance to fire exposure. It is available in a
3/8-inch thickness with a face size of 16 48 inches.
Insulating gypsum lath is plain gypsum lath with alu-
minum foil laminated to the back face. It serves as a plaster
base, an insulator against heat and cold, and a vapor barrier.
It is available in 3/8- and 1/2-inch thicknesses with a face size
of 16 48 inches.
Radiant heat lath is a large gypsum lath for use with
plaster in electric cable ceilings. It improves the heat emis-
sion of the electric cables and increases their resistance to
heat deterioration. It is available 48 inches wide, and in 1/2-
and 5/8-inch thicknesses and lengths of 8 to 12 feet. This
type of lath is used with plaster that is formulated for use
with electric cable heating systems.
Estimating. Gypsum lath is sold by the sheet or 1,000 sf.
The estimator will calculate the number of square feet
required (the square yards of plaster times nine equals
square feet), and divide by the number of square feet in a
sheet. Note the type and thickness required. Depending on
the number of jogs and openings, about 6 percent should be
allowed for waste. The materials used for attachment must
be estimated, and a list of accessories must be made.
Metal Lath. Metal lath is sheet steel that has been slit and
expanded to form a multitude of small mesh openings.
Ordinary, expanded metal lath (such as diamond mesh, flat-
rib lath) is used in conjunction with other supporting con-
struction. There are also metal laths that are self-supporting
(such as 3/8-inch rib lath), requiring no supporting con-
struction.
Metal lath is available painted, galvanized, or asphalt
dipped; sheet sizes are generally 24 96 inches (packed 16 sy
per bundle) or 27 96 inches (20 sy per bundle). Basically,
the three types of metal lath available for wetwall construction
are diamond, flat-rib lath, and 3/8-inch rib lath. Variations in
the designs are available through different manufacturers.
The metal lath should be lapped not less than 1/2 inch at
the sides and 1 inch at the ends. The sheets should be secured
to the supports at a maximum of 6 inches on center. The
metal lath is secured to the steel studs or channels by the use
of 18-gauge tie wires about 6 inches on center. For attach-
ment to wood supporting construction, nails with a large
head (about 1/2 inch) should be used.Diamond Lath. Diamond lath is an all-purpose lath that
is ideal as a plaster base, as a reinforcement for walls and ceil-
ings, and as fireproofing for steel columns and beams. It is
easily cut, bent, and formed for curved surfaces. It is avail-
able in weights of 2.5 and 3.4 pounds per square yard; both
sizes are available in copper alloy steel either painted or
asphalt-coated. Galvanized diamond lath is available only in
3.4 pounds per square yard.
Flat-rib lath is a 1/8-inch lath with “flat ribs,” which
make a stiff type of lath. This increased stiffness generally
permits wider spacing between supports than diamond lath,
and the design of the mesh allows the saving of plaster. The
main longitudinal ribs are spaced 1^1 ⁄ 2 inches apart, with the
mesh set at an angle to the plane of the sheet. Available in
copper alloy and steel in weights of 2.75 and 3.4 pounds per
square yard, and in galvanized steel in a weight of 3.4 pounds
per square yard, it is used with wood or steel supporting
construction on walls and ceilings, and for fireproofing.
The 3/8-inch rib lath combines a small mesh with
heavy reinforcing ribs. The ribs are 3/8-inch deep, 4^1 ⁄ 2 inches
on center. Used as a plaster base, it may be employed in
studless wall construction and in suspended and attached
ceilings. Rib lath permits wider spacing of supports than
flat-rib and diamond lath. This type is also used as a combi-
nation form and reinforcement for concrete floor and roof
slabs. Copper alloy steel lath is available in 3.4 and 4.0
pounds per square yard, and the galvanized is available in
3.4 pounds per square yard.Specifications. The type of lath, its weight, and finish
must be checked. The spacing of the supporting construc-
tion will affect the amount of material and labor required to
attach the lath. The type and spacing of attachment devices
should be checked as well as a list of accessories.Estimating. The metal lath is taken off by the square
yard in the same manner as plaster. It is usually quoted at a
cost per 100 sy with the weight and finish noted. For plain
surfaces, add 6 to 10 percent for waste and lapping; for
beams, pilasters, and columns, add 12 to 18 percent. When
furring is required, it is estimated separately from the lath.
Determine what accessories will be required and the quan-
tity of each.