Los Angeles, Los Angeles County,
California, USA
The seismic upgrade of a contemporary office building in downtown Los Angeles called on our' technical expertise in selective masonry removal to be utilized in the salvage and later reinstallation of over 1,200 panels of 1 1/4" thick Danby marble, with losses of original marble panels limited to under 2% of the total material.
The marble panel restoration required the use of a diamond chain saw to selectively salvage the panels. Repairs and dutchman patching of anchor holes were carried out on site in preparation for later reinstallation. Epoxy-fabric seismic treatment (FRP) was applied to each previously exposed column. Use of this system instead of thicker cocrete or shotcrete allowed us to put each panel back in the original plane of installation.
The Federal Office Building in downtown Los Angeles is a classic 60s structure with a marble-clad column system that was part of the general seismic improvement program taking place at the site over several years.
The upper portions of the columns were not removed but this shot shows the typical installation system used at the time of original construction. Unfortunately for the long-term viability of the lower columns this solid mortar backup acted as a holding pen for moisture penetrating throught the joints between marble panels.
Rust-jacking had damaged several panels on the lower column areas.
Normally in a cavity-system installation (empty space behind each panel), we can get behind the panels to cut the wire or metal ties securing each panel. In this case that solution was not feasible, so we turned to a specialty tool originally developed for the quarry industry, the diamond chain saw.
Here we are seeing a typical hydraulic power unit with a smaller version of the saw we ulitmately used to selectively salvage over 1,200 marble panels, each 1 1/4" thick.
Our cutting system required the use of special geared bars, attached to the wall, to support efficient and accurrate cutting. The protocol required the installation of anchors through original marble on only one of four faces on each column.
After the first face was removed top to bottom, the remaining three faces could be completed without coring small holes in the marble facing.
Here the first face has been removed and the backup masonry exposed for additional demo to remove all cladding material back to the original concrete-clad steel I-beam.
Removal continued methodically on each face until the bottom three stories of each column was exposed.
Selective demolition of the back up mortar on each column completed the remvoval and preparation process for the subsequent seismic upgrade.
All panels were handled carefully and stored on site to minimized potential loss.
Repairs and dutchman patching of anchor holes were also carried out on site in preparation for later re-installation.
Meanwhile the epoxy-fabric seismic treatment (FRP) was applied to each previously exposed column. Use of this system instead of thicker cocrete or shotcrete allowed us to put each panel back in the original plane of installation.
Prior to installation, we also upgraded the shelf angle support system, with angles installed at every course of marble.
After cleaning and restoration, each panel was upgraded with stone support blocks glued to the back.
Here, the first course is being installed.
Work was continued in a regular fashion until all columns had marble reinstalled.
New, thicker shelf angles accompanied the vertical progress
The division line between our work and upper marble panels is clear in this image. Ultimately the rest of the building and marble cladding will be cleaned to make the appearance more uniform.
Detail trim made from the same material finished off the bottom and completed each column.
In the initial project plan, all this material would have ended up in a landfill. Loss of fewer than 20 panels out of 1,250 was a satisfying way to limit the construction debris from this project.
