Cob: tabby ?

[Douglas Ketler Scheffer]

Well,  here is what I have to offer you as an unofficial expert on TABBY. I
grew up in Florida and spent countless hours of my youth climbing around
the ruins of old castles and fortresses built by the First Period Spanish
explorers to the area.

Sometimes I would come across students and professors of archeology,
architecture and various excavating crews from state universities studying
these ruins. Being the inquisitive youth that was; I'd stop and chat with
these folks.

They always referred to the wall composite as TABBY or COQUINA and
explained that it was made of shells, held together with a mixture of sand,
water and lime or at least the mortor was in some cases. There are
different degrees of coquina depending on how it was formed and where it
was found. The different composition requires different treatments.

The most commonly used shell that was used in the region that I grew up in
was in fact coquina shell (phonetically co-kee-na.). coquina shells look
like tiny oval clam shells about 1/4 to 1/2 in length and come in a
wonderful rainbow of colors. These shells also cover huge stretches of
shoreline along some Florida beaches and are broken up in the sand. (Feels
great to walk on. The shells break easily under the weight of your feet and
can't puncture the skin.)

Walter Marder, an architect with the Florida Division of Historical
Resources, has studied coquina's use from the history of the construction
of the Castillo de San Marcos beginning in 1672 to the present. He said
'Coquina is a survivor. It is a beautiful stone, and I will take it over
any others any day of the week. Why it isn't used more frequently is mind
boggling to me.''

The Spaniards would pour this mixture of shell, sand, lime and water into
huge molds to form bricks. These molds created bricks that were approx. 4'
x 3' x 3'. I imagine these were a real "drag" to move once they dried. But
hey, they had all of those newfound slaves to help out. They also pulled
coquina out of a quarry, as whole compressed bricks.

I have seen the bricks stacked with and with out mortor between them. A
wonderfully preserved example of this type of structure is a fortress in St
Augustine beach Fl. Located on the eastern coast between Daytona Beach and
Flagler. I imagine Flagler College there may have even more info on this
than I have provided.

Walter Marder found there was a resurgence of its use in decorative public
and private projects including arches, building facades and walls in the
1920s and 1930s. Part of its lack of popularity, as a building source is
its availability. St. Johns County, for example, has one active quarry
owned by Greg Wilson. Wilson's Lakeview Dirt Co. on Holmes Boulevard has
been providing coquina for the National Park Service restoration of the
Castillo de San Marcos and Fort Matanzas National Monument.

Coquinas future is at risk as a building material because changes in water
tables and modern household conveniences such as air conditioning may
affect its future. Rising damp, a phrase coined by architects, explains one
of the perils of coquina, a condition where moisture gets into the case of
coquina and is wicked up through the porous stone.

Air  conditioning can cause this by either drying out the stone through the
distribution of air in a building, or by water from the air conditioner
draining into the coquina. When rising damp happens, the coquina's dampness
tends to cause breakthroughs in plaster walls that cover the stone. Coquina
was never meant to be exposed to outside elements. The Castillo in St.
Augustine was originally covered with plaster as are virtually all coquina
buildings still in existence. The plaster serves as an exterior protectant
for the coquina, to prevent moisture from getting into the walls.

Like any other building material, coquina needs maintenance, the kind of
maintenance depends on the stone's use and the effects of natural and
man-made conditions on it. The issues of coquina's future were the subject
of a recent national conference in St. Augustine. The conference's purpose
was to bring together people with expertise in building materials and
construction to help those who preserve ancient buildings understand
treatment methods.

 For example, because of the wicking effect bringing moisture into the
stone, there is a need for reinforcement of coquina walls. In the 1950s,
steel rods were inserted in some buildings. But those rods rusted because
of the rising damp syndrome. Today's reinforcement of choice is stainless
steel rods.

There are also several kinds of coatings that can be applied to exterior
and interior walls. For some restoration projects involving coquina
buildings, Some have recommended the installation of concrete curbs where
the building's edge meets the street. That way, the
Possible water runoff from the street will not seep through plaster cracks
and into the coquina. The protective coatings and the concrete curbings
allow for the exterior barriers to moisture prevention.

But as too much moisture causes problems for plaster over coquina, coquina
that is too dry can crumble.

A second conference may be held in another two years to review the outcomes
of studies and research on coquina that will now be conducted throughout
the state and in other states.

 Part of what the state will be doing in the next year will be to identify
where coquina structures are and how they have behaved over the centuries.
The inventory, will provide
 a bank of information. Not only will the state have a master inventory. It
also will have an understanding of where the coquina was used, how it was
used and how it is faring in modern times.

Most of this information was gathered from articles on the web and in print
that I collect on traditional building techniques. I'm sorry I can't
reference the source. I am terrible about keeping footnotes

Good luck,
Douglas


>Go'day cobbers.
>Here is a question to all.
>I just this AM discovered this definition of "tabby" as a building material.
>Sounds pretty local & natural to me.
>I realize it's not cob, but thought it might be something the list might
>like to chew on a bit.
>So if anybody knows a bit about this, please share it to the list.
>......
>TABBY = (in the region of) South Atlantic U.S. -  A mixture of oyster
>shells, lime, sand, and water
>used as a building material.
>
>regards to all
>
>john fordice
>TCCP