Mission National Bank

Mission National Bank: Mission National Bank is a financial institution occupying a National Register-eligible Greek Revival temple style building in the Mission District at 3060 16th Street in San Francisco.  This image shows the building after renovation.  The gray finish reflects the original paint color from 1920.
Mission National Bank: Built in 1920 of precast concrete block cladding tied to a concrete and steel skeleton, it was finished with gray paint.  After many gray paint recoatings, the finish was removed about 1950 by aggressive sand blasting that also removed the smooth surfaces of the concrete and seriously eroded the decorative trim.
Mission National Bank: This image was taken during a heavy downpour where the façade is completely soaked.  The bolt penetrations, repointing, injection grouting, and extremely weathered surfaces are so well blended together that all we see is the beauty of the architecture.
Mission National Bank: The building was left this way having lost its protective surfaces against the harsh wet coastal weather of the region, beginning a systematic deterioration which went unchecked until a sizable piece of the cornice fell to the ground prompting the bank to commission emergency repairs.
Mission National Bank: Image of decorative concrete trim fractured by expanding steel reinforcement.
Mission National Bank: Image of the frieze. The frieze was made of individually cast pieces that were cemented onto the face of the concrete block. The cast pieces were reinforced with steel rebar and wire that were placed too close to the surface. The concrete quality of the casting was probably okay until the protective outer skin was sandblasted off, allowing CO2 to move deep within the concrete which carbonated the
Mission National Bank: The large steel bar corrosion has deeply fractured the poured-in-place concrete band.  Worker is pointing at a section that actually separated and fell away from the building.
Mission National Bank: Detail 1, close up view after loose pieces of concrete were removed exposing the corroded rebar and concrete substrate that supports the cladding.
Mission National Bank: Detail 2, after removing loose concrete pieces and debris, steel reinforcement was cleaned to white metal and a protective two coats of KEIM Concretal MKH anti-corrosion mortar was immediately brushed over the cleaned surfaces.
Mission National Bank: Detail 3, moving around the corner to the south-facing side the steel has been cleaned and coated with KEIM Concretal MKH anti-corrosion mortar. Note the two bolts securing the decorative trim in place.  Over the concrete block cladding of the front and south-facing side of the building, over 3300 bolts were bored and epoxied into the concrete substrate.
Mission National Bank: The holes were dampened with water, filled with KEIM Universal Mortar S, and textured to roughly match the surrounding surfaces.
Mission National Bank: Image of the precast cladding with the filled bolt head cavities.  Normally this is a serious aesthetic issue that is difficult to overcome with ordinary finishes and silicate coatings. KEIM recommends our silicate base coat with coarse fillers called “Grob” that blends these filled holes and other concrete patches together with the existing surfaces so they are not apparent, even as t
Mission National Bank: Finished southwest corner of the building.  Fine details are retained even after two coats of KEIM Concretal W silicate coating.  KEIM silicate coatings chemically bond to the concrete and cement forming permanent bonds.  The natural beauty of KEIM coatings spreads the light across surfaces for soft, even illumination.  Concrete elements retain their concrete appearance, not lost to the coating wh
Mission National Bank: In this image at the building’s southeast corner, the surfaces retain the building’s natural historic fabric without telegraphing the surface repairs.
Mission National Bank: The restored façade of Mission National Bank. Image taken at 9 AM as the sun was rising above the surrounding buildings.  Note the color is influenced by the warmth of the sunrise.  Careful inspection reveals the actual color of the façade which was matched to the original gray concrete color.
Mission National Bank: Mission National Bank as it appears when wet. Repairs are blended together to for a cohesive historic appearance. Note the thousands of cladding bolts are not visible, even in the rain.
Mission National Bank
Pictured above: Mission National Bank is a financial institution occupying a National Register-eligible Greek Revival temple style building in the Mission District at 3060 16th Street in San Francisco. This image shows the building after renovation. The gray finish reflects the original paint color from 1920.

About This Project

Built of precast concrete blocks tied to a concrete and steel skeleton in 1920, the surfaces were sand blasted in 1950 removing the gray paint and smooth concrete surfaces. Water infiltration corroded the reinforcement steel spalling the concrete and corroding the metal ties holding the cladding to the building. Emergency repairs were commissioned in 2009 when a sizable chunk of the cornice fell to the ground.
Challenges

Water infiltration over the last 60 years carbonated the concrete cladding and decorative elements, removing the protective alkaline passivation layers that protected the steel reinforcement and ties that held the cladding and elements to the framework. Expansion from corrosion of the reinforcement fractured decorative concrete elements, source of the object which fell to the ground. The cast pieces were reinforced with steel rebar and wire that were placed too close to the surface. The concrete quality of the casting was probably okay until the protective outer skin was sandblasted off, allowing CO2 to move deep within the concrete which carbonated the protective alkaline passivation layer surrounding the steel reinforcement. Sandblasting allowed rain water to be drawn by capillary action into the concrete carrying oxygen that corroded the steel, thus expanding its size. This is the force that fractured the concrete’s structure causing ultimate failure.

Solutions

The renovation work was focused on removing delaminated and spalled concrete, to repair or replace the steel reinforcement, protect the steel reinforcement from corrosion and make in-kind concrete repairs, rebuild delaminated decorative concrete elements, attach each concrete block with two bolts to the underlying concrete substrate, restore surfaces where the bolts were drilled, and provide a highly vapor permeable water repellent coating system having a natural concrete appearance that would, in this geographic location, last for at least 30 years before recoating.

Architect Architectural Conservator
Architectural Conservation, Inc., Berkeley, CA tel. (510) 849-3811
Historic Consultant
Tim Kelley Consulting, San Francisco, CA timkellyconsulting.com
Engineer
Bonza Engineering, Inc., San Francisco, CA bonzaengineering.com
Contractor Sneed & Company Construction, Inc., 2 W Seaview Ave, San Rafael, CA
tel. (415) 515-4115
Construction Expediting Services:
B&B Contractors Services LLC, Pacifica, CA bbcontractors.com
Applicator Sneed & Company Construction, Inc. 2 W Seaview Ave San Rafael, CA tel. (415) 515-4115
Type of Project Historic Restoration
Customer Mission National Bank
3060 16th Street
Location San Francisco, California (United States)
Regional Info San Francisco has unique a Mediterranean climate producing a wide variance of micro-climates throughout the area, generally characterized by moist mild winters and dry summers.

Products Used in This Project

Spezial Verdunnung
Spezial Verdunnung
A special primer and diluent.
 
Restauro-Fuge
Restauro-Fuge
Joint replacement material, especially for natural stone masonry, but also for clinker or sand-lime bricks.  Mineral dry bagged joint mortar with hydraulic binders.
 
Restauro-Top
Restauro-Top
KEIM Restauro-Top is a natural stone/masonry replacement material for surface zones. Mineral dry bagged restoration mortar with hydraulic binders. 
 
Universalputz Fine Historic Mix Plaster/Stucco
Universalputz Fine Historic Mix Plaster/Stucco
Universalputz Fine is a thin layer, interior and exterior plaster and stucco based on a unique formula of hydraulic lime, white Portland Cement and mineral fibers/fillers.  Meets requirements of CSIII (P II acc. to DIN 18550). Serves as the base for KEIM Mineral Silicate paints and finishes, for a complete plaster/stucco system for historic restoration or new construction.  
 
Concretal-W Coarse Base (Concretal-Grob)
Concretal-W Coarse Base (Concretal-Grob)
Concretal-W Coarse Base used as a first coat to fill small cracks and equalize textures
 
Faceal Oleo HD Protective Coating
Faceal Oleo HD Protective Coating
Clear coating that can be cleaned with pressure washer. This nano-technology will not let oil, grease or dirt penetrate the substrate, therefore making it easy to clean. Can be used on floors or walls.
 
Restauro-Giess
Restauro-Giess
For reproducing ornamental figures and parts by casting in molds.  Mineral dry bagged restoration mortar with hydraulic binders.
 
Silan 100 Penetrating Water Repellent
Silan 100 Penetrating Water Repellent
Solvent-free, silane-based water repellent to ZTV-ING OS-A and to DIN EN 1504-2/1.1, 2.1, 8.1.
 
CONCRETAL-W HIGH PERFORMANCE FINISH
CONCRETAL-W HIGH PERFORMANCE FINISH
Sol-Silicate Finish for All Concrete
 
Fiber Mesh
Fiber Mesh
Glass fiber mesh fabric, especially engineered to work with KEIM renders.
 
Concretal Dilution/Thinner (Concretal Fixativ)
Concretal Dilution/Thinner (Concretal Fixativ)
KEIM Concretal-Dilution is a sol-silicate thinner/diluent and primer for the Concretal coating and stain system.
 
Concretal Fine Filler
Concretal Fine Filler
Fine filler for KEIM Concretal concrete repair system to ZTV-ING TL/TP BE PCC and TL/TP OS and DAfStb guidelines.
 
Concretal MKH-20kg
Concretal MKH-20kg
Corrosion protection for steel and bonding bridge for KEIM Concretal Mortel R
 
Concretal Mortel-R
Concretal Mortel-R
Fibre-reinforced repair mortar for the KEIM Concretal concrete repair system to ZTV-ING TL/TP BE PCC I-II and to DAfStb guidelines for load classes M2 and M3.
 
Concretal Universal Mortar
Concretal Universal Mortar
Concrete repair mortar for general repairs
 
Concrete Cleaner
Concrete Cleaner
A silicic acid-based cleaning agent for concrete surfaces, which, when applied, reacts to form harmless compounds.
 
Lime Remover (Atzflussigkeit)
Lime Remover (Atzflussigkeit)
KEIM Ätzflüssigkeit (lime remover) is a pre-treatment and cleaning agent based on silicic acid, which, when applied, reacts to form harmless compounds.