of the two classes.
b. Class PM Systems are typically composed of a 6
mm to 9 mm (1/4 inch to 3/8 inch) thick, rigid,
polymer-modified cementitious base coat, a
polymer-coated fiber mesh, and a cementitious finish
coat. They are most commonly used over an extruded
expanded-polystyrene (XEPS) insulation board which
is mechanically attached to the substrate. Class PM
systems have good puncture resistance, but are
susceptible to damage from blunt impacts. The XEPS
insulation allows less water vapor movement.
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NOTE: A second type of EIFS, which is commonly
referred to as "drainable," is available from most
EIFS manufacturers. These drainable systems are
either Class PB or Class PM systems that are
designed to provide an avenue for flow and drainage
of incidental moisture from the wall assembly.
Each manufacturer has taken a different design
approach to achieve drainage of moisture from their
systems. ASTM D2273, Standard Test Method for
Determining the Drainage Efficiency of EIFS Clad
Wall Assemblies has recently been published.
Currently there is a limited history of performance
for these drainable systems in actual building
constructions.
The drainable EIFS systems were originally developed
as a solution to applying EIFS over water sensitive
substrate materials such as wood sheathing and
gypsum sheathing meeting ASTM C79. Wood sheathing,
C79 gypsum sheathing, and other water sensitive
sheathing materials are not, however, allowed under
this specification, and for certain substrate
materials (for example, over existing masonry), a
drainable system may not be required.
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NOTE: The following references may be used for
additional information on EIFS:
Guide to EIFS Construction, EIFS Industry Members
Association (EIMA), Morrow, GA, 2000.
Interim Design Guidance for Exterior Insulation and
Finish Systems (EIFS), USACE Technical Instructions,
TI 805-15, 2003
Nelson, Peter E. and Richard E. Kroll, Exterior
Insulation and Finish Systems (EIFS): Materials,
Properties, and Performance, ASTM STP 1269, American
Society for Testing and Materials, Philadelphia,
SECTION 07240
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