Let's All Get Along
The world is full of experts. Some we listen to, others we try to ignore. It also seems more and more experts arrive on the scene daily. It has less impact on the tried-and-true assemblies but is fertile ground for new frontiers.
As building practices are shifting to a greater use of rigid insulation over metal framing to provide a thermal barrier and limit thermal bridging, the market is abuzz with experts who each claim to know the best practices. This is different construction for many of us and everyone has an opinion or some expert advice. While we should be open to new ideas and progression, I do wish experts would stick to their respective fields and heed the advice of other experts in theirs.
The rigid foam people are experts in foam: they know how to make it, how it works and about energy transfer. Yet, they really are not the authority on stucco or EIFS. The requirement for more rigid insulation over framing, better known as Continuous Insulation, is listed and written as a cladding neutral design. This means the code is neutral on the cladding that covers the foam but does not infer that all claddings are the same or even equal. You should not simply use the same procedure for wood or vinyl siding as you would for cement stucco. It’s not just swapping claddings.
EIFS is another whole change. First, EIFS is the cladding and CI all in one operation. The thermal bridging is gone with adhesively applied EIFS. This is an undeniable fact. Cement stucco is also unique to other claddings over rigid foam. A successful installation requires adjustments. I have worked with general contractors who have never done cement stucco before but completed hundreds of buildings with other sidings. They tend to think it is simply a matter of switching wood for stucco; that’s a sure recipe for disaster.
Most claddings want the water resistant barrier over the foam and while that may work great with other claddings, it is generally not recommended for cement plaster by plaster bureaus. It is very similar to placing cement plaster over masonry substrates; a WRB, such as housewrap or building paper, is not recommended and proven to be problematic. The plaster industry and the rigid foam industry seem to have varying opinions over this issue.
I recently was told that the IBC forbids cement plaster directly applied to fiber panels. That may or may not be true but rigid foam is not a fiber panel. ASTM C-926 specifically allows cement plaster to be applied to lath over “rigid foam board-type products.”
The plaster industry has expertise in plastering; lots of experience. We know about cement plaster over rigid foam, as it has been done successfully as a one-coat stucco system in the southwest for more than 40 years. The one-coat stucco manufacturers have tested and proven that cement over foam with the WRB under the foam performs very well. They also tested one-coat cement stucco with the WRB over the rigid foam and the results were disappointing. All this leads one to ask, “Why do the foam people not listen to the plaster experts?”
Stay In Your Lane
Let the plaster experts be the experts in plaster. We won’t tell you how to make or install foam. We won’t interfere with how the dew point is affected or what foam has the best R-value. We just ask that you heed our advice on how cement plaster works best with your foam, how EIFS is a complete CI cladding or how to install a successful one-coat stucco. We have done it for years and we are really good at it.
Both industries support CI as we want more energy efficient structures. How about we respect one another’s areas of expertise? Many on the other side want more testing. Lab testing is nice and can help with the unknown, but the best test is real life projects. Ones that have withstood the test of time and we have lots of them to show. Failures and successes, and we investigate why they fail or why they succeed. Most of the time the explanation for the failure or success of the wall assembly is not nearly as scientific as some would hoped it would be.
My advice to people coming into our world of plaster—please listen to us, you will profit and save yourself, the architect and building owners a lot of grief. We have some great systems and one to fit every need, design or desire.