Defining the Challenge
Upon completion of a high-rise residential structure, cracks and delamination appeared on exterior surfaces of the tower compelling building owners to initiate a lawsuit against the general contractor. The contractor, in turn, blamed faulty materials used by subcontractors. With so many subcontractors involved in this large construction project, it seemed an almost impossible task to pinpoint the cause of the materials failure. The question that eventually arose was whether building materials or faulty workmanship was to blame. RJ Lee Group was retained by a law firm representing one of the manufacturers of packaged building materials used in the construction and asked to examine the building’s stucco system and underlying build-out materials, undertake the task and perform failure analysis to determine the cause(s) of the cracking and delamination.
RJ Lee Group’s petrographic experts used a combination of analytical techniques in accordance with the ASTM methods for petrographic examination of hardened concrete including visual examinations, optical stereo-microscopy, polarized light microscopy (PLM) and/or scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS). We tested not only material samples removed from the building, but also newly purchased, unhydrated build-out material and stucco with and without the additive that had been used in construction of the high-rise. We studied both product formulation data and production information and reviewed reports prepared by experts for the Plaintiff, the contractor and the subcontractor. We also developed accelerated tests to reproduce color variations seen in samples of the build-out material and to determine if the resulting color change produced a change in volume since stucco strength can be compromised through volume changes.
In examining the three different types of build-out materials used to level various areas of the building, we discovered that there was no correlation between micro-cracking observed in these materials and the defects produced. We did observe paint in shrinkage cracks indicating that the cracking occurred during curing or shortly thereafter which meant that these cracks occurred before painting and were caused by improper application of the stucco.
When we evaluated the stucco we observed shrinkage cracks caused by hydration and moisture loss as well as excessive water loss in both the stucco and build-out materials. We also determined that the improper mix of the stucco scratch coat was responsible for the high porosity of the applied mixture and that the stucco was not properly cured. This was evidence of improper mixing and application of the stucco.
Upon further examination of the scratch coat where the delamination plane occurred, our expert observed a layer of laitance—fine particles often found on the surface of cementitious materials when too much water is used. We were able to reproduce this laitance by over-mixing stucco with twice the recommended amount of one of the build-out materials proving that it had not been combined in correct proportions as directed in the mixing instructions. Based on this observation, the failure was the result of either over-mixing of the build-out material and/or an excess of water.
Our petrographic scientists were able to use our own in-house laboratory capabilities to explore the necessary scenarios that eventually provided the evidence as to why and how the delamination and cracking were taking place. Our failure analysis investigations uncovered multiple workmanship issues: build-out materials were not properly leveled resulting in variation in stucco thickness; fiber mesh was improperly embedded in the scratch coat resulting in delamination; the substrate layer was not roughened to provide adherence for the next layer and it was not properly cleaned prior to stucco application. These conclusions provided evidence that the manufacturer of the material was not responsible for the failure of the materials but rather that the stucco was not applied correctly—a result of poor workmanship. The improper application of the scratch coat caused the weakness that resulted in the delamination and cracking.