The Original roof system ( slightly east of
Nashville )
The crew
Testing for entrained air
Applying retarder
Casting on vibrating table
De-molding the next day
Washing the retarded concrete off of the aggregate
The finished product (ends still need washing)
New Antefix Close up
of exposed aggregate
The Parthenon Re-Roof
Nashville, TN 1997
Undoubtedly the most challenging production job I have worked on during my career. This full sized replica of the original Parthenon was built in Centennial Park in the 1920's using both cast-in-place and precast concrete with an exposed aggregate finish. All of the cement covering the colored aggregate was removed with brushes while the concrete was "green" because chemical retarders had yet to be invented.
A representative of the leading Cast Stone producer on the east coast and I attended a pre-bid meeting and presented our ideas on how to tackle the job. His company wanted to dry tamp the pieces and apply a surface retarder after the piece was removed from the mold. I believed that the only approach was to wet cast the job using the traditional method of applying retarder to the mold, allow the retarder to dry and then wet cast the piece. This entailed one piece per mold per day whereas the dry method proposed by my competition allowed multiple pieces per mold day(typical dry tamp ). These different production methods were significant differences since 9000 pieces were required.
We both submitted bids and I lost.
But to my amazement 18 months latter the winning bidder called and asked if my wet cast price was
still good. Fortunately I had kept the bid file. What had occurred was
that he was unable to make an approved sample using his dry tamp method.
My company prepared samples using wet casting and had approvals within 45 days.
The challenge was now to set up a dedicated production facility for only this job . Prior to
the
approved samples the only exposed aggregate I had even done was a flat sign and 8 bollards.
Now was the time to call the retarder expert,
Gregg Roche at Master Builders. With his help we selected a water based retarder because it would not attack the plastic and urethane molds.
Exposed aggregate is relatively easy to accomplish on horizontal surfaces but much more
difficult on vertical and sloped surfaces. All of the 9000 pieces hade exposed vertical sides. To get the aggregate
evenly distributed on all surfaces you have to fine tune the mix design,
maintain consistent slump and vibrate just enough to consolidate the mix but not abrade the
retarder from the mold.
Working closely with Gregg and our
vibrating table supplier all of these hurdles were jumped. Metro Parks ( the owner ) and their Q.C.
consultants wanted test cylinders made from each batch each day and tested. They contracted
with a local testing lab to pickup the cylinders and perform the tests. All pieces were labeled so that
date of production and batch could be identified if tests should determine a bad batch. In a year of
production and over 1000 batches not one
cylinder broke below the required 6000 PSI.
In addition to crush tests our production foreman, Louis, tested the
entrained air for each batch.
The production was organized much
like an automobile assembly line where there are work stations and the work comes to the worker.
All production and Q.C. documents were in both Spanish and English because the crew was
entirely Hispanic.
The final challenge was to ship
9000 tiles in such a way at to get them there in one piece and facilitate their installation profitably
by the roofing contractor. Carlton McGrew of Young Sales, the installer, commented that
only 1/2 of 1% (45 tiles) were broken and that we had made his job much easier and
more profitable.
The production photos on the left were obtained from the project's owner.
Production
By: Architectural Art Stone
Parthenon
website: