DIAMOND MESH. The terms diamond mesh
and expanded metal refer to the same type of lath
(fig. 7-4). It is manufactured by first cutting staggered
slits in a sheet and then expanding or stretching the sheet
to form the screen openings. The standard diamond
mesh lath has a mesh size of 5/16 by 9/16 inch. Lath is
made in sheets of 27 by 96 inches and is packed 10 sheets
to a bundle (20 square yards).
Diamond mesh lath is also made in a large mesh.
This is used for stucco work, concrete reinforcement,
and support for rock wool and similar insulating
materials. Sheet sizes are the same as for the small mesh.
The small diamond mesh lath is also made into a
self-furring lath by forming dimples into the surface that
hold the lath approximately 1/4 inch away from the wall
surface. This lath may be nailed to smooth concrete or
masonry surfaces. It is widely used when replastering
old walls and ceilings when the removal of the old
plaster is not desired. Another lath form is paper-backed
where the lath has a waterproof or kraft paper glued to
the back of the sheet. The paper acts as a moisture barrier
and plaster saver.
EXPANDED RIB. Expanded rib lath (fig. 7-4) is
like diamond mesh lath except that various size ribs are
formed in the lath to stiffen it. Ribs run lengthwise of
the lath and are made for plastering use in 1/8-, 3/8-, and
3/4-inch rib height. The sheet sizes are 27 to 96 inches
in width, and 5-,10-, and 12-foot lengths for the 3/4-inch
WIRE MESH. Woven wire lath (fig. 7-4) is made
of galvanized wire of various gauges woven or twisted
together to form either squares or hexagons. It is
commonly used as a stucco mesh where it is placed over
tar paper on open-stud construction or over various
Lets now look at the basic installation procedures
for plaster bases and accessories.
Gypsum lath is applied horizontally with staggered
end joints, as shown in figure 7-5. Vertical end joints
should be made over the center of studs or joists. Lath
joints over openings should not occur at the jamb line.
Do not force the boards tightly together; let them butt
loosel y so the board is not under compression before the
plaster is applied. Use small pieces only where
necessary. The most common method of attaching the
boards has been the lath nail. More recently, though,
Figure 7-5.-Lath joints.
staples have gained wider use (due mainly to the ready
availability of power guns).
The nails used are 1 1/8 inches by 13 gauge, flat
headed, blued gypsum lath nails for 3/8-inch-thick
boards and 1 1/4 inches for 1/2-inch boards. There are
also resin-coated nails, barbed-shaft nails, and
screw-type nails in use. Staples should be No. 16 U.S.
gauge flattened galvanized wire formed with a
7/16-inch-wide crown and 7/8-inch legs with divergent
points for 3/8-inch lath. For 1/2-inch lath, use
Four nails or staples are used on each support for
16-inch-wide lath and five for 2-foot-wide lath. Some
special fire ratings, however, require five nails or staples
per 16-inch board. Five nails or staples are also
recommended when the framing members are spaced
24 inches apart.
Start nailing or stapling 1/2 inch from the edges of
the board. Nail on the framing members falling on the
center of the board first, then work to either end. This
should prevent buckling.
Insulating lath should be installed much the same as
gypsum lath except that slightly longer blued nails are
used. A special waterproof facing is provided on one
type of gypsum board for use as a ceramic tile base when
the tile is applied with an adhesive.