The board-formed concrete facade of the decorative exterior had deteriorated significantly and needed cleaning, patching, and new surface treatments to preserve and restore the surface to its former Deco glory.
After each area of spalling was cut and the damaged concrete removed, the steel rebar was wire-brushed or sandblasted, and then coated with an epoxy-based anti-oxidant coating to retard future oxidation.
Wikipedia Reference:
http://en.wikipedia.org/wiki/1932_Summer_Olympics
This was the typical condition encountered on our first visit to the site: slight dislocation of the concrete surface, usually on a pattern-like basis.
Each location usually revealed a significant amount of internal damage due to the 'Iron Jacking' or rusting and decay of the internal steel reinforcing bars.
Here is another example of the same typical pre-project condition. Remember that we were asked to evaluate this structure and facade prior to the erection of scaffolding or other access, so our estimate for the budgeting process was understandably somewhat short of the final total of repairs
In each case the identified re-bar deterioration was identified once the scaffold access allowed hands-on survey and examination.
Each location was marked with a red crayon to mark out the lines of selective demo for concrete cutting.
After cutting the concrete to an average depth of approximately 3/4", the segmented demo area was chipped out using low-impact, small pneumatic hammers equipped with carbide-tipped chisels
Larger areas of demolition required the use of larger demo tools, but still keeping the rate-of-impact to a relatively low level
After each area of spalling was cut and the damaged concrete removed, the steel re-bar was wire-brushed or sandblasted, and then treated with an epoxy-based anti-oxidant coating to retard future oxidation.
Here is a typical sequence of spall repair and patching. The first step is the cutting of the concrete area to an average depth of 3/4"
Here the repair area has been properly chipped out and is ready for the application of the anti-oxidant coating prior to application of patching mortar. Note that all cuts are either horizontal or perpendicular, to assist in orienting the patch with the original horizontal board-formed technique, and to hide the final appearance of the repair.
Here the repair mortar has been installed and is being allowed to cure. We did not go the extra measure of matching the color of the repair mortar to the original concrete color since the architects had approved a repair scheme that involved coating the entire facade afterward.
We also performed other types of concrete repairs using similar methods, such as at this old water fountain, suffering from the same degradation of steel reinforcement bars.
Here we have prepped and coated the steel bar on the interior and then installed the specified patching mortar.
These decorative urns were also damaged by the same decay mechanism
Rebuilding these rounded shapes required a multi-staged process.
Stainless steel threaded rods inserted into the body of the urn provided a stable anchor to support the stainless steel mesh. This in turn provided a relatively rigid platform for the reproduction of the original form in repair mortar.
The damaged cap portions of the urns were re-adhered using stainless steel threaded rod and epoxy adhesive
All of the visible concrete surfaces on the entire project received a 'rendering', in this case a Portland cement-based thin coating (approx. 1/16" thick) that provided a uniform color and also enhanced resistance to future moisture penetration.
This image shows a rendered surface on the left, and the original board-formed concrete surface on the right. The intent was to provide a protected historic fabric without excessive modification of the surface character.
The 1932 Olympic Swim Stadium was originally designed with a 15-20 year life-span in mind. Our efforts have hopefully exceeded that design parameter.
