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Moravian College • Preservation Master Plan
Corrosion of Reinforcement
Corrosion of the metal reinforcement in concrete is
inhibited by the high alkalinity of the surrounding
cement paste. An oxide film forms over the steel
and prevents further attack. Sufficient concrete
covering on the reinforcement will further inhibit
corrosion. The protective alkalinity of the concrete
can be disrupted by lowering pH values through
carbonation, cracking, or loss of the surface concrete.
Carbonation is the reaction of carbon dioxide with
the cement paste, which forms calcium carbonate.
This reaction significantly lowers the pH of the
concrete. If the zone of carbonation reaches the
reinforcement, it can disrupt the protective oxide
layer and induce corrosion. Corrosion can also occur
if other problems, such as cracking, delamination,
or spalling, disrupt the concrete cover and allow
water to reach the embedded metal.
Concrete Repair and Replacement
Concrete repair work, whether its purpose is to
repair cracks, delamination, or spalling, install
large replacements, or repair rusting reinforcement,
usually involves removal of deteriorated material.
Deteriorated concrete must be removed using
methods that do not damage surrounding sound
concrete. Impact methods may cause new cracking
in adjacent sound concrete. Cutting methods or
small, hand-held chipping guns are preferred
methods.
The surface of the concrete and reinforcement to be
repaired must be properly prepared. Inappropriate
preparation of concrete surfaces is the primary
cause of failure for concrete repairs. The concrete
surfaces to be repaired must be clean, free of
dust, and roughened to promote a mechanical
key with new concrete. Embedded, rusting
reinforcement must be exposed to the full extent of
the corrosion. The rusting reinforcement must be
cleaned of all corrosion down to clean metal. The
cleaned reinforcement should be painted with a
rust-inhibiting coating.
New concrete can be placed using conventional
cast-in-place methods, through shotcrete methods
for large areas, or by hand-troweling or groutinjection
repairs for smaller areas. Repair mixes
must be formulated to match the strength and
appearance of existing material and also have low
shrinkage. In important building elements, such
as entrance porches, the exposed aggregate finish
must be matched. Concrete that does not have an
exposed aggregate finish may be coated with a
silicate mineral paint or other breathable masonry
coating to cover repair work.
9.3 Masonry
The majority of the historic buildings at Moravian
College are constructed with brick or stone
masonry, which helps define the overall Germanic
architectural style of the area. Most of Moravian
College’s historic stone buildings have load-bearing
masonry walls and are constructed of regionally
available, rough faced stone. Stone has also been
used as foundations on many brick buildings, or to
emphasize architectural features on facades. Smooth
limestone is used as an accent material for door
thresholds, window sills and lintels, water tables,
and capstones. Bluestone and greenish brownstone
are also seen as trim elements on certain buildings.
Brick is perhaps the most common material used for
historic buildings at Moravian College, including
most of the Priscilla Payne Hurd Campus and
Hamilton, Memorial, Monocacy, and Zinzendorf
Halls at the North Main Street Campus.
Even though masonry is durable, proper care
should be taken to ensure its long-term survival.
Exterior walls respond to the effects of rain, wind,
sun, and temperature and their stability underpins
long-term preservation of the building. Masonry
maintenance is not just an aesthetic consideration
but a structural one. As with all historic materials,
frequent evaluation and careful maintenance can
solve minor problems before they become large
and expensive repairs. The preservation approach
emphasizes retention and repair; any necessary
replacements should be made in-kind, matching
the existing in color, texture, size, and other visual
qualities. Each masonry material has its own design
and maintenance issues that should be considered.
Stone
Stone was used to construct the oldest and most
prominent historic structures at Moravian College,
including the 18th-century Single Brethren’s
House and the Widows’ House, and the Comenius
Hall group from 1891-1907. Also, many of the
brick buildings on campus have rough stone
foundations using stone that was quarried locally.
Natural stone has a variety of physical properties,
depending on its type, place of origin, and method
of quarrying. Stone is a long-lasting material, but
John Milner Associates • October 2009 • Chapter 9 • Building Guidelines • 283