The Metal Lath Newsletter
Volume 04, Issue 03, March 2004

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Foundation Weep Screeds Versus
Punched One-Coat Casing Beads

Punched One-Coat Casing Beads; How it Originated and Why it’s Not the Best Product Choice

As three-coat stucco became more and more expensive and many of the EIFS systems became problematic for contractors a new one-coat stucco system evolved. It was originally billed as a substitute for three-coat stucco systems offering better flexural strength and crack resistance due to the addition of acrylics and chopped fibers for reinforcement and better consistency since everything was included as a bagged product. While many of these systems are merely thin versions of traditional three coat stucco systems with few of the added benefits that were touted early on, their development came with new product requirements. Some of these products don’t meet ASTM C1063.

In an effort to reduce cost the manufacturers and developers of some of these systems further reduced the system quality by using lathing products that were not technically considered as stucco lath products. These would include 1.75 lb expanded metal lath and 20 gage one inch woven wire mesh. Since these early systems were nearly always installed to a thickness of 3/8 inch in finished thickness, the metal lath and vinyl bead industries did not yet manufacture accessories to fulfill the requirements of the new systems. In particular there was not a traditional foundation weep screed available in 3/8 inch thickness available to the stucco industry. The reason is simple; before the one-coat stucco systems came into existence there was not a need for accessories with lower grounds.

Because these were unorthodox systems that didn’t meet the requirements of ASTM C1063 or any of the model building codes there was only one way to gain code acceptance. Each company had to test their system’s performance on an “as built basis” and prove that it would work even though non-code approved products were an integral part of the system. Once these systems received an approval report based on the way the system was tested the various system manufacturers were forced to have their systems installed exactly as tested in order to meet the requirements of the approval report. Those that tested with the lighter types of lath and punched casing beads in lieu of lath and accessories not approved by ASTM C1063 were forced to follow their approval report and that is how the one-coat punched casing beads came into popularity as a replacement for foundation weep screeds. Of course that fact that the punched casing bead is much less expensive doesn’t hurt the popularity of this bead product. In fact many contractors have been requesting larger sizes thinking it is permissible to use them in three-coat work.

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Why Doesn’t the Punched Casing Bead Work?

The punched casing bead has two 900 returns in the form of the ground and the return flange. The shape alone forms a dam the bottom of the wall that tends to trap water rather than allowing it to exit the cementitious membrane, especially if the paper is placed over the flange of the casing bead. Secondly, the holes placed in the ground of the casing bead fill with wet stucco when the section is stuccoed and this nearly always results in plugged holes that will allow little or no moisture to escape.

What is the Difference in the Foundation Weep Screed, and Why Does it Work Better to Remove Moisture?

As discussed in the December 2003 issue of this newsletter in detail, the foundation weep screed is described in ASTM C1063 as an accessory used to terminate stucco at the bottom of exterior walls. “This accessory shall have a sloped, solid or perforated ground or screed flange to facilitate the removal of moisture from the wall cavity and a vertical attachment flange not less than 3 1/2 in. long”. Note that the sloped surface can be punched or solid. This is because the holes in the surface do not facilitate the removal of moisture, but rather the entire surface of the angular ground serves this purpose. The holes only serve as bonding holes to aid in the bonding of the stucco to the foundation weep screed. As the stucco cures and hydrates it shrinks in volume slightly and results in a small crack or fissure between the surface of the angular ground and the stucco. Since the building paper is placed over the back nailing flange during installation, any incidental moisture that reaches the building paper can run down the wall to the slope of this bead and exit the cementitious membrane.

Note that it is important if an acrylic or Elastomeric finish is applied to the stucco surface that the installer or painter is careful not to fill the crack at the junction of the stucco and the foundation weep screed with finish that might hinder the escape of moisture.

Below you will find a photo of a foundation weep screed that has been installed on a framed wall. Also you will see two drawings depicting the proper foundation weep screed installation and the punched casing installation that is not recommended by the author to be used as part of any stucco system.


Foundation Weep Screed Located
at Bottom of a Framed Wall



Punched Casing Bead Incorrectly used as a
Foundation Weep Screed

"The author offers no warrantees, implied, stated, or expressed regarding the information found in this article including techniques, construction methods, drawings or materials identified in this article. To the best of his knowledge the information within is correct and up to date as of its publication date. The author is not responsible for typographical errors. This article is protected by all copyright laws and shall not be photocopied, stored in any electronic format or distributed without express written consent of the author. All rights reserved by Metal Lath Consulting Co, LLC."





Past Issues:
January 2004
December 2003
November 2003
October 2003
September 2003

 

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The answers to commonly asked metal lath installation questions derived from job experiences and client questions.

 
 


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