Precast Stone Restoration, Preservation -- Los Angeles, CA

Pasadena, Los Angeles County,
California, USA

This precast stone restoration project for the historic headquarters of Carnegie Observatories in Pasadena followed an earlier restoration in the 80s, which left the stone vulnerable to damage. High-pressure water cleaning had scoured the original cement surface and left the cast stone trim more absorbent and prone to deterioration when exposed to moisture. Application of special rendering compounds stabilized these surfaces and made them much more resistant to weathering.

Wikipedia Reference:
http://en.wikipedia.org/wiki/Carnegie_Institution_for_Science#Observatories_of_the_CIW

Click on images below to enlarge.

The Hunt Building of the Carnegie Observatories was in need of stabilization of decorative cast stone trim due to the previous mistreatment.
A previous restoration in the 80s had cleaned the cast stone surface with pressurized water, but the technique went overboard and ended up removing the cementitious ‘skin’ that is often present when Portland cement-based Cast Stone units are pulled from the mold. Removal of this skin made the porous and absorbent nature of the cast stone matrix more prone to damage and decay from acid rain and other atmospheric pollutants.
Our solution to this loss of original surface was to apply a ‘rendering’ using a color-matched repair mortar and applied in thin layers. Custom-made profile trowels were used to match the original decorative profile of the trim units.
Use of such a proprietary material is appropriate in order to protect the original building fabric, but it must be carefully cured and protected during the installation process. Here we are applying moisture during the critical period of 72 hours after installation.
Here a transition point between planes graphically illustrates the procedure of covering and protecting the deteriorated substrate.
Here is the same corner finished and ready for final treatment.
In addition to repointing of all joints between masonry units, final treatment included the application of a penetrating sub-surface water- and oil-repellent treatment to all rendered cast stone surfaces to enhance resistance to the penetration of acid rain and atmospheric soiling.
This same technique was used to address the failed and stained cast stone surfaces at decorative entries and windows.
We were privileged to work on two Myron Hunt buildings at the same time, this structure as well as the Huntington Museum.