There is a potentially disturbing trend in the cement plastering industry. While ground zero appears to be Florida, there is potential it could impact the entire United States stucco market. One major homebuilder from the Sunshine State has become so concerned that they have temporarily halted the use of cement stucco on homes, even in Texas.
Conclusions have apparently been reached as to the cause and solutions to the Florida stucco crisis and are under way. The real concern should be that the conclusions to the cause may be missing the real problem. The consensus from the building science community seems to be that traditional cement plaster over framing, even with two layers of water-resistant barrier, is inadequate. This conclusion fails to explain success in other regions. The cry that it is only successful due to the arid climate ignores historical success in northern cities like Seattle or Chicago and continued use in central Europe to this day.
A lack of comprehension and the disregarding of facts are likely built on these two inherent motivations:
Make it simple: People want simple explanations. This is exacerbated with powerful decision makers.
Special agendas: Most people look at a problem and think, “What is in it for me?” Even the major home developer has an agenda. While they want to solve the problem, a secondary goal is to shift the risk. This agenda can lead to product or systems based solutions. This is made more palatable as manufacturers and consultants tend to agree for their own interests. The problem with these solutions is they are costly, do not address root cause and may or may not work.
Mastering Plaster
The art of plaster has always been blending science with craft. Plaster is unlike most claddings, it is manufactured on site. Ignoring science or craft is a recipe for failure. Why did it work for so many years before? An example of missing the craft link is the micro fissure issue. Science through the forensic work has discovered cement plaster is not as water-tight as it once was. This is primarily due to the micro fissures found in several modern samples of stucco basecoats. These are thousands of very small cracks in the cement membrane that can allow moisture to pass through and overwhelm the water-resistant barriers. Why do we have micro fissures today?
Most plaster mixes today tend to be too cement-rich. The cement paste shrinks as water evaporates and the result is micro fissures from shrinkage. Old school craft plasterers overcame this problem by compacting the basecoat at the right time. This floating procedure was done with a hard wood shingle, cork or neoprene hand tool. The process can only be done when excess mix water has left the newly applied basecoat. The process requires timing and being done with the right tool. Properly done hard floating compacts and will densify the cement membrane. This floating process closes the micro fissures, making the plaster highly crack and water resistant. Some ignore the importance of this step due to principle two.
Education and training will make stucco better, but where is the profit and how does this shift the risk? The preferred path seems to be more complexity in the design and detailing. This opens doors to new products, more consultants and an ability to shift the risk. I am reminded of a consultant who told me that he agreed his design and details were indeed complex, but it wouldn’t be his fault if it failed.
Regardless of what scientists or consultants propose and the developers demand, the rubber meets the road on the job site with the worker blending his mix and installing it. I am perplexed as to how more complication with less site education and training will result in a more trouble free cladding.
Complexity will not only increase installation costs, but new unforeseen problems will certainly arise. Failing to study the craft as well as the science of cement plaster is failing to comprehend the real problem. Historians like to say that failing to study history is dooming you to repeat it. We are likely at the time in stucco history that our actions or lack of same will determine stucco’s ultimate future. If we fail to implement craft education and training, others will continue to step in. Their solutions are likely to impact codes and standards for the next generation.
