There is one other issue that has resulted in plaster being problematic to apply, no matter what is mixed and how. And that is the move in America from a masonry- to a frame-building community. Frame construction has movement built into it, yet Portland cement doesn’t move very well. That's the bad news; the good news is that the exterior insulation and finish system has stepped in to fill the gap, so to speak, embraced by the architectural and buying communities. The acrylic-modified Portland cement and the 100 percent acrylic basecoat material provide more flexibility for the systems that can manage the movements of wooden frame houses. The resulting marriage between frame building and the very flexible EIFS has been beneficial to one and all.
Portland cement on frame construction, especially in areas with temperature variations and thermal shock, inevitably results in a lot of cracking. Metal and wooden studs can accommodate a calculated amount of wind load or "deflection." The amount a particular stud can deflect, without twisting on its axis, is based on its size, length, weight, etc. Stucco can accommodate the movement of a studs with an L1360 deflection. Some structural studs, metal or wood, can easily accommodate much greater loads. To use Portland cement for plastering frame buildings therefore requires heavier gauge or wider studs to accommodate these deflection criteria.
A contractor from Arizona highlights the quality of the wood as an additional problem. "The greatest degree of cracking is directly related to the framing with wood constructions. Wood is of terrible quality these days because they can't produce it fast enough. Two days after it's unbunked and erected, it
Twisted and warps. That makes it real tough on the plasterers. I'm president of our association, and I hear a lot of complaints about it."
While agreeing that green wood causes cracks due to shrinkage in the framing itself, two contractors from Colorado and Louisiana highlighted other issues with wood-framed houses: "If they don't leave a gap between the sheet that's recommended by the plywood association, then there's a potential for swelling. If the stucco is done prior to the loading of a roof, there's a weight/cracking issue. And whether the drywall inside is done before or after the stucco makes a difference, too. A Tennessee contractor pointed out that cracks also result when architects do not design in enough expansion joints, because they want a monolithic appearance.
EIFS to the Rescue
AWCI CONSTRUCTION DIMENSIONS MAGAZINE JANUARY 2000