Page 321 - Construction Waterproofing Handbook

EXPANSION JOINTS 6.23

FIGURE 6.22 Substrate block-out installed to facilitate installation of expansion
joint. (Courtesy of Emseal Joint Systems)

Preformed metal joints for stucco are available in a variety of designs and metals. The
most durable metal is zinc, which does not corrode like galvanized metal. Zinc materials
withstand greater substrate movement than plastic or PVC materials.
A typical cross section of a stucco control joint is shown in Fig. 6.27. The metal lath
flanges are used to attach joints to substrates and are secured in place when stucco is
applied over flanges. Flange sides should be secured to separate and structurally break the
sides of a substrate to allow structural movement, Fig. 6.28. Applying both flanges to the
same structural portion will defeat the expansion joint purpose.
When vertical joints intersect horizontal joints in a facade, they should not be broken,
Fig. 6.29. Breaking the horizontal joint instead will prevent the water running down the
facade from entering at joint intersections. These intersections should be monitored during
installation, as this is the most likely area of infiltration.
Stucco substrates often separate from preformed joints due to differential movement
between the materials. This results in cracking along joint faces, allowing access for water
infiltration into a structure and its components.
Unfortunately, to repair what might be perceived as a leaking joint, metal joints are
often filled with sealant. This restricts joint movement capability and does not address the
immediate problem.
In all types of vertical envelope surfaces, expansion and control joints should be placed
at changes in plane or direction, at intersections of dissimilar materials, around substrate
openings, and where allowances are made for thermal movement or structural movement.

Heavy-duty metal systems
Manufacturers also provide horizontal expansion joints that are designed specifically for
heavy-duty wear or use. These typically include such installations as parking garages, espe-
cially at loading dock areas, and interior decks subject to forklift or other heavy equipment.
These systems are usually complete metal fabrications, since the systems described in
the previous sections could not withstand this type of abusive life-cycle conditions. These
joints require blockouts to be installed in the concrete slab for installation. The joints
expand and contract by the use of a flange that permits the top of the joint to slide back
and forth as required, as shown in Figs. 6.30 and 6.31.