Los Angeles, Los Angeles County,
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.
A little work with a chisel exposed the inner reinforcing steel bar without much effort.
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 20's, they used a standard casting technique, in which the mold is prepared and then a thin mortar of cast stone mix (approximately 1/4") is applied to the face of the mold. A later mix of cast stone mortar is then poured to fill the mold 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.) occurred 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 molding 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 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 compromised. 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-repellent sub-surface treatment that rendered the surfaces highly repellent 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.