 This crack is being measured. Structural cracking, whether static (nonmoving) or dynamic (moving) should be caulked to prevent water entry into the glazed architectural terra-cotta system. Photo: NPS files. |
Repair of addition and structural damage: Holes, sign anchors,
slots for channel steel, or structural cracking in the surface
of glazed architectural terra-cotta cladding should be permanently
sealed with a material that will expand with the normal dynamics
of the surrounding material, yet effectively keep water out of
the system. Any one of a number of commercially available waterproof
caulking compounds would be appropriate for this work. Holes and
static (non-moving) cracks may be caulked with butyl sealants or
acrylic latex caulks. For dynamic (moving or active) cracks, the
polysulfide caulks are most often used, although others may be
safely employed. It is, however, important to remember that these
waterproof caulking compounds are not viable repointing materials
and should not be used as such.
Temporary replacement: Temporary replacement measures should be
implemented when missing units are scheduled to be replaced but
work cannot be undertaken immediately. Lengthy delivery time,
prorating of work or seasonal considerations may postpone replacement
work. Severe deterioration should at least be ameliorated until
work can begin. Temporary repointing, removal and saving of undamaged
units to be reset later, or the temporary installation of brick
infill to retard further deterioration might be considered.
Removing earlier repairs: Removing earlier repairs may be necessary
when the work has either deteriorated or has become visually incompatible.
Cementitious stucco, caulkings with black bituminous compounds
or brick repair work may become structurally or visually unstable
or incompatible and should be removed and properly rehabilitated.
Replacement of glazed architectural terra-cotta: Replacement of
severely spalled, damaged, or missing glazed architectural terra-cotta
elements is always difficult. Certainly, in-kind replacement is
advisable, but it has a number of drawbacks. Stone, fiberglass,
and precast concrete are also viable choices, but like in-kind
replacement, also have their inherent problems.
Several notes on replacement: When replacing glazed architectural
terra-cotta, all of the original deteriorated material should be
completely removed. Half bricks or similar cosmetic replacement
techniques are not advised.
-- When possible and where applicable, replacement units should
be anchored in a manner similar to the original. Both structural
and visual compatibility are major considerations when choosing
replacement materials.
-- Removing and re-anchoring damaged glazed architectural terra-cotta
is an extremely difficult if not impossible task. The complexity
of the interlocking system of masonry units, backfill, and metal
anchoring system precludes the removal of the glazed architectural
terra-cotta unit without destroying it.
-- Re-anchoring deteriorated units is likewise impossible. Therefore, if the terra-cotta in
question is loose, severely deteriorated, or its structural integrity
in serious question, it is best removed and replaced.
In-kind replacement is possible today, but only on a limited basis.
Most new glazed architectural terra-cotta is machine made, not
hand made as the original. Thus, the porous tile body of the new
material tends to be more uniform but less dense and often not
as durable. The glaze on the new glazed architectural terra-cotta
tends to be thinner than that on the older material and subsequently
more brittle. Machine processing has also produced a glaze that
is uniform in color as opposed to historic glazes which were slightly
mottled and, therefore, richer. Visual compatibility is an important
consideration when replacing in-kind.
Only a fairly limited inventory of in-kind pieces is presently
available for replacement such as plain ashlar blocks and the
simpler details such as cappings and sills. When deterioration
severely damages the more ornate pieces (urns, cartouche work,
balusters, etc.) either expensive hand casting or alternative
materials must be sought. There is a tendency today to replace
damaged ornamental work with simpler, cheaper and more readily
available units. This decision cannot, however, be supported,
as the removal of this work inevitably diminishes the character
and integrity of the building. Another major consideration in
choosing in-kind replacement is the question of delivery time,
which is often quite lengthy. If new glazed architectural terra-cotta
is chosen as a replacement material, the architect or building
owner should plan far in advance.
"The Preservation of Historic Glazed Architectural Terra-Cotta" an Historic Preservation Brief
