Solution
Inspection showed that the galvanized steel facing of the cornice was in repairable condition but that much of the applied zinc ornament was not salvageable. The trusses supporting the cornice, the steel tee purlins and the structural clay tile were generally in excellent condition.
Three of the components of the metal cornice which required replacement because of serious deterioration are shown in this view. They are the lions' heads on the crown molding (several are missing due to failed soldered joints), modillions, and the egg and dart molding at the base of the cornice. The brake-formed galvanized steel that comprised the lineal moldings of the cornice, the soffit and dentil band were in sound condition. Photo: Richard Pieper.Budget estimates were prepared for repair-in-kind and for replacement of the cornice. The architects considered two replacement alternatives; one with new metal and one with glass fiber reinforced plastic. Repair of the existing cornice facing was the most economical alternative. The New York City Landmarks Preservation Commission also favored repair rather than replacement.
Repair of the cornice included replacement of all modillions and nearly all applied zinc moldings; installation of new galvanized steel crown molding and cornice roof edge details; placement of new roofing on the top of the cornice; insertion of new rod hangers to supplement existing wire hangers supporting the face of the cornice, and repainting both the interior and exterior.
Work Description
Visual examination of the exterior of the cornice with binoculars showed that significant sections of stamped molding had previously separated from the galvanized steel substrate and had fallen or been removed. From the interior of the cornice, it was not possible to closely examine the remaining applied zinc ornament other than the modillions. The height and depth of the cornice also made it impossible to examine all portions of the front face of the cornice from swing stage scaffolding. For these reasons, a 20' long fixed tubular scaffolding tower was erected on sidewalk bridging to facilitate inspection of a representative portion of the exterior.
The scaffolding was left in place after the inspection and was eventually incorporated into construction scaffolding. Two scaffolding work levels were required: a lower level to work on modillions and molding replacement below the soffit, and an upper level to replace roof edging, crown molding, and lions' heads.
Paint Removal
Existing paint was flaking and peeling. Because most of the zinc ornament was to be replaced, it was not necessary to remove paint from the entire cornice facing. Consideration was given to chemical, heat, and water spray removal techniques, but chemical removal was dismissed because of environmental and public safety considerations and potential problems of the residue soiling the exterior masonry.
A water spray was used to remove most of the paint from the components of the cornice that were being retained. With the more delicate egg and dart molding, care was required to avoid possible dimpling of the metal. Steps were taken to keep water from collecting inside the cornice. Photo: Michael Devonshire.Tests of water spray removal techniques showed that successful cleaning was achieved with a rotating tip spray device, which removed nearly all paint without harming the metal substrate.
Care was required when spraying the zinc molding that was to remain, since the water pressure required to remove the paint was sufficient to dimple the projecting metal of the ornament. To avoid dimpling of small egg and dart moldings, the contractor only removed loose paint from these elements. Water and paint chips were collected in troughs of sheet plastic. Paint residue was gathered to the extent possible, but the spray effluent was difficult to control and some spilled onto the building and sidewalk bridging. In some areas it was necessary to supplement water removal with light hand scraping, using a flat scraper after most paint had been removed.
A number of factors contributed to the success of the cleaning and paint removal technique. Because the cornice on this building was accessible from behind, it was possible to monitor and remove any excess water that penetrated various openings in the cornice caused by deterioration. Weep holes at the base allowed water to seep out of the cornice. For other projects where less extensive work is required and particularly where the cornice is backed with wood, other paint removal and cleaning methods may be necessary.
Ornament Removal and Fabrication
The historic zinc ornament originally was soldered in place after the galvanized facing was raised and installed. In most cases moldings were continuously soldered but in some cases only tack-soldered in place. (Soldered joints generally were in good condition even though moldings had deteriorated.) Deteriorated moldings were removed by de-sweating joints with propane torches.
New stamped zinc ornament closely resembling the original was available in stock sizes from a Midwest manufacturer. In some cases it was necessary to gang two moldings (an 8" egg and dart and 3" bead and disk moldings for instance) where a larger original molding had incorporated two designs. Modillions were the only zinc elements requiring significant assembly prior to installation.
Modillions were comprised of 6 stamped pieces, which were soldered together in a shop by the contractors prior to installation. While preassembled ornament was available from the manufacturer, assembly by the installer greatly simplified shipping and assured that mounting flanges met installation requirements.
Since the new stock modillions did not incorporate a leaf molding at the top as did the originals, it was necessary to attach new mitered leaf molding sections to the top of each modillion. New galvanized steel back-up was attached at the top of the modillions for better anchoring to the soffit and to avoid riveted zinc to zinc joints which might fracture in this location (as did the originals due to metal fatigue).
New modillions were the same size (24"L x 22"H x 12"W) as the originals, but were not precisely the same design. This difference in appearance is not discernible from the street below. (New molds matching the original modillions could have been fabricated at additional cost if this had been necessary for authenticity.)
Ornament Repair and Installation
The new ornament was attached to the existing galvanized steel backing with stainless steel pop rivets. This method of attachment is standard in the sheet metal industry today and is much simpler for field application than soldering.
By using rivets instead of soldering, it wasn't necessary to clean the steel backing to bright metal. Both the galvanized steel facing and the zinc ornament were primed with zinc dust/zinc oxide primer prior to rivetted installation.
Detailed section shows the supporting technique for the new modillion, which consisted of riveted galvanized steel flanges and threaded rods.Drawing: Michael Devonshire. Click here to see a larger version of this drawing.Pop rivets were set through flat surfaces on the top and bottom flanges of each molding and were spaced no further than 6" apart. Modillions were pop riveted to the soffit through the new galvanized backing used to support the leaf moldings. New galvanized steel flanges attached the modillions to the entablature. Variations from 90 degrees in the soffit/entablature angle were taken up by the new rear flanges at the entablature. New galvanized steel crown molding at the top of the cornice and new galvanized steel backing for the leaf molding at the base were attached to the existing galvanized facing with stainless steel stove bolts, rather than rivets, because of the weight of the sheets.
The 1 1/4" x 1/4" ferrous armatures to which the cornice facing was bolted were lightly rusted, but in satisfactory condition. The original system of twisted wires which attached these armatures to the trusses was also in good condition, but appeared haphazard. Additional threaded rod and clamp anchors were added to supplement these wires. Rods were also added to attach modillions to the soffit in the event that the new leaf molding flange rivets broke.
Repainting
The existing cornice was painted dark brown. Examination of finishes on sheltered areas of molding clearly showed that the cornice had originally received a buff sanded paint finish, which was intended to imitate stone and to complement the buff hues of the terra cotta and limestone. A slightly darker color than the original was chosen for repainting since it would not readily show soiling and would complement the appearance of both cleaned and uncleaned facade masonry.
Because it seemed likely that paint maintenance of the cornice would be neglected, a zinc dust/zinc oxide primer was selected to give the cornice a measure of galvanic protection if the paint film was compromised. The primer was used on all surfaces, including the back of the new ornament and the interior of the cornice. The primer and two coats of alkyd finish paint were brush applied.
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