Peforated Wallcovering.
Comparing Permeability.
Permeability is a measure of the amount of water vapor (moisture) that can pass through a specified area of material in a certain amount of time. The measure and degree of permeability is expressed in units referred to as Perms. Materials with higher Perm levels allow more moisture or water vapor to pass through than those with lower Perm values.
While the construction industry has yet to recognize a single test procedure, the ASTM E-96-00 Standard Test for Water Vapor Transmission of Materials is being used by many companies to measure the permeability of their products; permeability values can vary substantiality depending on the test method used. Also, testing results can vary widely unless a strictly controlled and consistently applied test protocol is followed. There are several ASTM E-96 test procedures but the most commonly used test is the water cup (wet cup) method which tests for the permeability of the wallcovering itself (film and backing).
Using this ASTM test method, wallcovering perforated using the OMNOVA perforating system achieved the following permeability levels (an average of samples taken across the web of a roll of perforated wallcovering):
While these Perm values can provide general guidance, testing the permeability of a particular wallcovering construction under controlled laboratory conditions does not account for the many variables that can affect wall system permeability under installed building conditions.
The following graph compares average Perm levels between high quality OMNOVA perforated wallcovering and competitive perforated wallcovering as shown by outside third party testing:
The actual permeability of any particular perforated wallcovering will be impacted by the thickness or weight of the wallcovering, the specific type of embossing and the type of wallcovering backing. In addition, the permeability of an interior wall (without wallcovering) can be affected by several factors, including wall construction, wall conditions and wall surface preparation (including the type, thickness and number of layers of paint or primer). If a wall already has low or no permeability, then installing perforated wallcovering will not provide any permeability benefit to the wall system. Some manufacturers will recommend a new wall surface be left unprimed to improve the permeability of the wall system. This may increase the overall permeability but may create other difficulties when wallcovering is removed or replaced.