William Penn Building
Los Angeles, L.A., California
Stabilization of Deteriorating Cast Stone Decorative Elements using Patching and Rendering Compounds.
Stabilization of the decorative cast stone components of the exterior skin of this 1914 residential hotel (since converted to apartments) was driven by the goal of arresting an already advanced decay process.
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A fatal flaw in the original mix design contributed to the uniform decay of all cast stone elements, and careful stabilization and rendering were required to preserve these important elements. |
Composed of brick veneer with decorative cast stone trim elements, the cast stone portion of the facade had failed uniformly and completely at the surface level, the most important level of interface with the elements. |
Moisture penetration over the years had caused the original surface material to fail. This was an unusual project for us in that the damage and decay mechanism was uniformly distributed over the entire building. The logical conclusion to this phenomenon was that the original mix design for production of the cast stone had likely been executed in a substandard fashion. |
This degradation was so widespread that deteriorating cast stone was observed at all locations and elevations and had advanced to a dangerous degree, in some cases posing a hazard to pedestrians below. |
The overall appearance of the facade was one of decay and neglect. |
In addition to the inherent material failure, the internal mild steel reinforcing bars had also contributed to the overall state of decay. This condition was evident on most of the horizontal window sills. |
In addition to the inherent material failure, the internal mild steel reinforcing bars had also contributed to the overall state of decay. This condition was evident on most of the horizontal window sills. |
This image shows a typical condition observed throughout the building facade: the delamination of the outer cementitious skin. When this material was originally manufactured in the 20s, they used a standard casting technique, in which the mould is prepared and then a thin mortar of cast stone mix (approximately 1/4") is applied to the face of the mould. A later mix of cast stone mortar is then poured to fill the mould completely. |
While we will never know exactly what mistakes were made in the fabrication of the original decorative cast stone, it is certain that some deviation from proper handling of Portland cement materials (hydration during curing, too much water-to-mix ratio, etc.) ocurred during the manufacturing process. |
Notice in this image how almost all exposed corners of the decorative cast stone trim have been weathered and rounded. Clearly this decay mechanism is uniformly widespread (unusual for most projects, as the material failures tend to be more localized), and this fact helped dictate a uniform response. |
This image is a clear illustration of how a limited solution can have unanticipated and dramatic consequences. We chose to restore the building surfaces using a similar technique of rendering described in the previous projects on this web page. This 'rendering' of a proprietary restoration mortar was thinned to allow for application by paintbrush. The cove moulding on the upper left of the image was removed to prepare the surface for the installation of new-cast matching GFRC trim. Notice that the Gothic tracery was never patched with mortar, but the application of uniform protective rendering made it seem to be almost fully re-created. This optical trick allowed us to restore the building facade for the owner without making the project so expensive as to preclude its execution. |
This image shows the areas where the replacement of original decorative trim was mandated by the deterioration of the original historic fabric. Obviously, the horizontal trim components were most seriously comprimised. This is not surprising considering the ability of any horizontal decorative trim element to trap moisture. Unfortunately for this building, the original cast stone components were inferior in nature from the beginning, and they had been removed over the years by previous 'maintenance' efforts in acknowledgement of this condition. |
After all original cast stone trim elements were rendered, they received a saturating application of a water-repellant sub-surface treatment that rendered the surfaces highly repellant to moisture and further degradation. This affordable-housing facility is now ready for another long period of providing shelter for the community, and also providing a glimpse of how our built environment looked in the era of our grandparents. |