Archive for the ‘Oakland stone’ Category

The balsawood boulders of the Kaiser Roof Garden

26 September 2016

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Ever since 1960 when the rooftop garden on the Kaiser Center’s garage, largest in the world at the time, was built, it’s been heralded by American landscaping pros, Kaiser Center employees and appreciative residents. After the garden’s recent rehabbing, now (specifically, any weekday) is a good time to visit.

Putting a garden on a roof, even one made of the best Kaiser reinforced concrete, takes careful design and execution. The heaviest plantings and features were situated directly over the strongest supporting columns.

Even so, the designers had to minimize the weight of everything. The soil, a blend of lava rock, expanded shale and peat moss, is practically potting mix. The concrete is a lightweight formula. And then there are these impressive boulders.

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Each one is a generously sized hunk of pumice, the nearest thing to balsa wood in the mineral kingdom. Well, diatomite is lighter, but so friable you can crumble it in your hands. Pumice, basically a foam of expanded lava, stands up to weather beautifully with its relatively inert glassy composition. And close up, it’s handsome.

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If you see this stuff in a landscaping-supply yard, kick it around or pick it up. It’s so light, you’ll feel like Superman — but pumice will cut your bare skin, so be careful.

Oakland building stones: Sandstone

19 September 2016

For many years, timber was the default material for Bay Area buildings. Only substantial institutions like governments, banks and a few wealthy churches were sheathed in masonry — solid stone — and time and again, earthquakes were their undoing. Sandstone was chosen for the walls of two major Oakland churches, First Baptist and First Unitarian.

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First Baptist, on Telegraph Avenue at 22nd Street, was one of Julia Morgan’s earliest commissions, although she didn’t have a say in its looks. The Romanesque Revival building, inspired by the Aachen Kaiserdom, was designed by another architect whose delays in getting it built led the congregation to fire him once the exterior walls were up, in 1904. The day the church was to vote on Morgan’s design for the interior was 18 April 1906, and early that morning the San Francisco earthquake badly damaged the exterior. She took on the job of rebuilding it, then finishing to her own specifications a magnificent sanctuary inside.

The stone, to all appearances, is from the Greystone Quarry south of San Jose. It’s the same golden sandstone of Eocene age (~35 million years) used for the core buildings of Stanford University and other landmark structures like the Carson City Mint in Nevada, Lick Observatory and the old San Jose Post Office, now part of the San Jose Art Museum. I wrote about this stone for KQED a few years back. The stone blocks have a rugged “quarry face” on the exterior but are nicely dressed on the sides. The flat sides qualify them as ashlars, as opposed to fieldstone like you’d use in free-standing stone walls.

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The building also suffered damage during the 1989 earthquake. In this view you can see the seismic bracing, covered in gray, on the north wall that was installed at the time.

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The First Unitarian Church, at 685 14th Street, was designed by Walter Mathews in the elegant Richardsonian Romanesque style. Construction began in 1890.

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Stone was an important design choice, inspired by “a spirit of civic pride.” All of the building’s materials were sourced in California. The sandstone is a thick veneer, in quarry-faced ashlars like first Baptist. However, the stone is a cool gray, very fine grained, and is apparently not from Greystone Quarry. Parts of the building are faced in neat rows (courses) and arches.

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This stairwell bay is pleasingly laid in random-coursed ashlars, a system that avoids a regimented look and is probably stronger too.

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At its opening on 6 September 1891, a hymn written for the occasion began with the verse,

“The forests gave their oak and pine,
The hills their stone and clay,
And fashioned by the builder’s art
Our temple stands today.”

The building suffered light damage in 1906 and 1989, but repairs in both cases took several years.

The church’s Historic American Buildings Survey (HABS) report is full of deep technical and historical detail.

In both buildings, the sandstone shows signs of deterioration after more than a century of exposure.

Oakland building stones: Verd antique

5 September 2016

California’s state rock is serpentine, and in this blog I’ve picked up, photographed and defended it against detractors. I’ve called serpentine beautiful, adorable, inspiring and more, but I’ve never called it a building stone. However, it can be.

Serpentine in its Sunday best is called verd antique. This closeup is from the iconic I. Magnin building at Broadway and 20th Street.

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It resembles a particularly psychedelic marble — a translucent deep jade-green shot with intricate white veins. Petrologically, though, it is nothing like marble and a lot like soapstone. It consists of magnesium-based silicate minerals that are harder and more chemically robust than the calcite or dolomite that makes up marble.

Verd antique is all over downtown Oakland, usually as a subsidiary element at the sidewalk level. The building on 17th Street between Telegraph and Broadway has a particularly large expanse of it.

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The Fox Theater building is another notable example. But in this post I want to draw attention to four buildings that do more with verd antique. The I. Magnin building (built 1930) naturally comes first, its entire first story richly faced with this stone.

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The Foulkes Building at 419 15th Street (built 1924) has a high facade of verd antique with bronze decorations.

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The Moyles-Kappenman building (built 1928), longtime home of Lobe & Velasco Jewelers, has a lovely front of verd antique on 1617 Broadway and an identical one at its other end on 1618 Telegraph.

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Finally we have the otherwise undistinguished Wells Fargo building at 2040 Franklin Street, where the public-facing elements (entrances and ATM) are framed in verd antique.

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The reason that all of these stones look the same is that for nearly a century a single quarry in Rochester, eastern Vermont, has been supplying the trade with Vermont Verde Antique(tm) stone. It is geologically special because it was squeezed two separate times, like twice-cooked fries, between colliding tectonic plates during the Paleozoic Era. As the supplier’s website puts it, it owes its origin to “highly sheared ultramafic rocks that have been rewelded and metasomatized by the process of serpentinization.” The lighter-colored “Cardiff Marble” serpentine from northern Maryland was once popular but is no longer produced. That stone is found in the White House’s Green Room, the National Archives rotunda and other places in Washington DC.

Verd antique gets its name from the Italian verde antico, “ancient green.” It was popular in Byzantine architecture. Oakland has a few pieces of European-style, brecciated verd antique to be seen here and there.

The stone industry considers verd antique a type of marble (it’s metamorphic and takes a polish) and follows ASTM standards for its manufacture, but verd antique is really its own beast.

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You can’t do much with California serpentine except admire it. For an example, see the ecstatic response of an out-of-state geologist to San Francisco’s Marshall Beach exposures.