Page 272 - Masonry and Concrete

Masonry Veneer

271
MASONRY VENEER

moisture, and most retain good flexibility even in low temperatures.
Thin plastic flashings are also easily torn or punctured during construc-
tion, so thickness should be a minimum of 20 mils, but preferably 30
mils or more. Puncture resistance can be added to plastic flashings with
fiberglass scrim reinforcement when it is embedded between two sheets,
and the overall required thickness is then greatly reduced. Metal foils
can also be combined with fiberglass-reinforced plastics to form light-
weight, durable flashings. Most recently, rubberized (or polymer modi-
fied) asphalt flashing materials have been introduced in the masonry
industry and have enjoyed ready acceptance from design professionals
and masons alike. The rubberized asphalt is self-adhering and self-
healing of small punctures. Once the workers become accustomed to
handling the material, it installs quickly and easily and is relatively
forgiving of uneven substrates. Thorough
cleaning of the substrate surface, however,
is critical in obtaining good adhesion. Metal
flashings such as copper and stainless steel
are more commonly used in commercial
construction, but on high-end homes, the
extra durability provided may justify the
additional cost.
Lengths of flashing should be lapped
3–4 in. and sealed so that water cannot
penetrate at the seams, and the flashing
should be continuous around both inter-
nal and external corners. PVC and rubber-
ized asphalt flashings cannot tolerate UV
exposure, so they are typically brought
beyond the face of the wall and then
trimmed flush after the masonry is in
place (Figure 7-23). It is important not to
stop the flashing short of the exterior wall
face, or water may not be properly drained
from the cavity. Rubberized asphalt flash-
ing, when properly adhered, prevents FIGURE 7-23
water from flowing back underneath the
Trim flexible flashing flush with face of wall after
membrane and re-entering the wall. A installation. (photo courtesy Brick industry Associ-
formed drip edge on metal flashing also ation).

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