Bubbling Stucco

Donald E. Smith, CCS

December 2005

I write as a concerned consumer. I’m having a problem with "bubbling and delaminating” of the stucco that was applied to my residence. I’m interested in knowing what may be causing this and what types of warranties the manufacturer and the application contractor usually provide.

As a preamble to the answer, I refer you to last month’s column about stucco. This particular question makes us look at the basics of an exterior envelope regardless of the materials involved and stucco in particular. The problem is definitely a moisture problem caused by the application of an exterior coating not suitable for the substrate to which it is applied. If you remember last month’s quotation from Gary Maylon’s book, Gary tells us that stucco is a breathable system. That is moisture vapor caught inside the system will make its way to the exterior face of the stucco and evaporate, and that the cavity must have weep screed installed at the bottom of the stucco.

For the case in question, I suspect two things have occurred. First, an exterior coating was applied to the stucco to obtain a color for the finished stucco. The coating, from your "bubbling and delaminating” statement, is in all probably an elastomeric coating that is vapor impermeable; the bubbling is caused by moisture trapped in the system and causing the delamination. Even if there is a weep screed in place, it may not be able to handle the amount of moisture in the system, or, the weep screed is blocked. This leads me to believe that moisture is entering the system from another source, which could very well be improperly installed flashing or a total lack of flashing.

Without proper flashing and a system of weeps at the bottom of the system, any external envelope system—regardless of the materials—will be doomed to failure because of moisture penetration. In most all cases, the exterior cladding or system is blamed as the source of the failure, and that is simply not the case. In this situation, there are two causes of the failure: first is the coating, and second is a hidden source of moisture penetrating the cavity behind the system.

The question of warranties goes back to the original contract for construction. Normally there is a one-year warranty for the total project. In a system like stucco, I am not aware of warranties covering a longer period of time being available.

Solutions to the problem would be to determine if the weep screed is in place and functioning properly, and that all other flashings are in place and functioning. Last, the exterior needs to be removed and replaced with a vapor permeable coating. There are many coatings available that fit the criteria and will perform quite well.

What are the structural and mold-resistant qualities relevant to EIFS for Densglass, Glassroc and gypsum board?

I assume that when you say gypsum board you are referring to gypsum sheathing and not gypsum board used for interior partitions. This assumption puts all the materials you are questioning into the exterior usage category. The fiberglass-faced sheathing boards will take exposure to the elements better than gypsum sheathing, which is a paper-faced product. AWCI’s EIFS—Doing It Right program has a method to test gypsum to determine delamination of the facing of the board to ensure damaged board is not used as a substrate for EIFS.

The question of mold resistance is easy to answer. Most, if not all, of the fiberglass-faced products indicate a rating of 10 (the highest rating available) as a mold-resistance rating when tested in accordance with ASTM D3273/D3274.

The structural integrity of the products is best determined by applying the requirements of the local building for the type of installation involved. I do not think a blanket answer will cover this situation. Most manufacturers of these products have test data available that you can apply to specific situations.

As for standards and preferences, ASTM has many standards that apply to gypsum sheathing and many tests to determine a product’s values for specific types of usage. As to preference of one material type over the other, this will usually be determined by the design professional or local building codes.

About the Author
Donald E. Smith, CCS, is AWCI’s director of technical services.