The Metal Lath Newsletter
Volume 04, Issue 01, January 2004

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Stucco Bands Can Lead to Major Water Intrusion Problems

What are Stucco Bands?

Stucco bands are architectural reliefs in stucco applications usually placed on large open expanses of stucco such as walls at floor levels, around windows, or as wainscoting to add an architectural flare to any stucco project.

The original stucco bands also known in some areas as pop outs, were merely wooden planks of varying sizes that were attached to the wall and covered in lath, corner beads, and stucco cement. If and when the band leaked the wood would rot and the lath would rust often causing a delamination of the lath and stucco. Some contractors are now replacing the wood with foam strips that are then covered with offset leg corner beads and strip lath prior to the stucco application. The wall and the bands are then stuccoed at the same time to achieve full embedment and to avoid cracks at the juncture with the wall. The top surface of the band should be sloped down and away from the wall to allow for drainage.

While banding applications have evolved to include special banding beads, or larger casing beads that are deeper than the stucco on the wall surface. These beads are placed opposing each other and then filled with stucco to form the band which is usually 1/2 inch to over 1 inch higher than the plane of the wall’s surface and are often finished in a different color than the wall. What I see quite often when the double casing bead method is employed are leaks at the junction of the wall stucco with the top casing bead or the casing on the outside edge of the window band. This leak occurs when the stucco shrinks away from the bead about 1/32 inch during the curing process. The crack is too small to accept a proper amount of caulking material to seal properly and yet large enough to allow sizable amounts of moisture to enter behind the cementitious membrane.

Also seen in the market place are bands that are placed on the wall after the lath, scratch and brown coat are installed. These bands can also be opposing casing beads that after installation are fitted with a lath strip between the beads and then filled with stucco. These can be problematic because the application of the beads requires that they be mechanically attached to the framing through the stucco that has already been applied. They often have a flat top flange that does not slope away from the wall and the bead has very little area to caulk at the juncture with the wall. However, with this application at least the water should not be able to enter the wall or get behind the cementitious membrane. At least one manufacturer of vinyl banding casing beads manufacturers one that has a sloped surface to facilitate the movement of water away from the wall.

Finally there are the EIFS types of foam bands that are applied to the surface of the brown coat of stucco. In some areas these can be purchased prewrapped and finished with a colored EIFS finish. In other areas the band must be cut to size, wrapped with fiberglass mesh and then finished with an EIFS type finish. Once complete the band can be attached with mastic to the surface of the brown coat and caulked along the top edge. The top surface of these bands should be sloped at least a few degrees, down and away from the building to provide drainage and a drip edge. Although these seem to be the best alternative for band installation, if they are not sealed properly at the juncture with the building they can leak behind the band and become detached in time. Foam bands that are simply wrapped and covered with the typical EIFS finish are not as durable as portland cement stucco bands. However the tradeoff is somewhat justifiable due to the reduced risk of water intrusion into the wall cavity.

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If the Band Leaks what are the Possible Repercussions?

Band leakage as with all stucco leakage can be disastrous to the overall wall system. However, if the entire system was installed according to ASTM C1063 and C926 including two layers of water resistant breathable building paper that was correctly installed, proper flashing around all openings in the stucco membrane that is complete and proper, foundation weep screeds at the bottom of all framed walls and if all of the other requirements of these codes have been met, then the redundant systems should be in place to make temporary small leaks rather insignificant. To say that is not to minimize the long term effects of water intrusion. It is imperative that a regular maintenance and inspection system be put in place after the job is complete by the project owner or their representatives to find and correct stucco leaks before they can cause catastrophic failure of the stucco system including the building paper and the sheathing and structural systems beneath.

Like all forms of construction cladding stucco requires maintenance. Caulking will not last forever and must occasionally be removed and replaced. Cracking to some extent is inevitable with all stucco systems. This is not to imply that large structural cracking is common. Rather it is important to state that cracks do occur in stucco installations and are not always the fault of anyone. Building movement, excess wind loads, movement of other components that apply stress to stucco can all cause cracks to occur. These cracks are often minute and require no action at all. In some cases however a structural crack that is wide and deep enough to cause moisture intrusion will appear. These cracks are generally wider than 1/8 inch and penetrate all layers of stucco down to the lath. These cracks should be filled with trowlable filler and patched as soon as they are discovered. Furthermore, the underlying cause of the crack should be investigated to see if more serious problems with the stucco or structural systems exist.

The designer and installer should not shy away from bands simply because they can be problematic, but rather should look for the best system to install and then make sure that the entire stucco system is installed correctly in compliance to codes and ASTM C1063.

"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."



Coming in the next issue:
Accessories: Control Joints Part 2

Past Issues:
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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