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Historic Preservation - Technical Procedures
Brick: Characteristics, Uses And Problems
Hspg Prepared For Nps - Sero
Brick Unit Masonry
Brick: Characteristics, Uses And Problems
BRICK: CHARACTERISTICS, USES AND PROBLEMS
This standard includes general information on the characteristics
and common uses of terra cotta and identifies typical problems
associated with the material along with common causes of its
Characteristics of Brick:
- Outer crust is harder and more dense than the inner material
- Long life when properly maintained
- Low maintenance when properly laid
- Available in wide rage of colors and textures
- May be cast in decorative molds
- May be carved
- Bricks used during the 18th and 19th centuries were soft and
porous; They absorbed 20-25% of their weight in water (by the
end of the 19th century, 10% or less was considered the
- Soft, underburned bricks may absorb as much as 35% of their
weight in water; The absorbency factor is important to know
when comparing modern bricks with old ones.
Typical historical and current uses for brick include:
- Structural uses such as foundations, walls and floors.
- Decorative/ornamenental uses: May be cast to form moldings
and other decorative features; may be carved; may be used in
a variety of colors, textures, bonds and joints.
- May be concealed by other finish materials such as stucco,
plaster or paint, or may be exposed both on the interior and
PROBLEMS AND DETERIORATION
Problems may be classified into two broad categories: 1) Natural
or inherent problems based on the characteristics of the material
and the conditions of the exposure, and 2) Vandalism and human
Although there is some overlap between the two categories, the
inherent material deterioration problems generally occur gradually
over long periods of time, at predictable rates and require
appropriate routine or preventive maintenance to control.
Conversely, many human induced problems, (especially vandalism),
are random in occurrence; can produce catastrophic results; are
difficult to prevent, and require emergency action to mitigate.
Some human induced problems, however, are predictable and occur
NATURAL AND INHERENT PROBLEMS
1. Cracking: May be caused by structural movement or settlement
of the building, use of too hard of a repointing mortar, or
differing rates of expansion and contraction between adjacent
2. Crazing: A pattern of tiny cracks; typical on glazed brick
due to the different coefficients of expansion and contraction
between the brick and the glaze. This is not usually a
serious problem unless the cracks extend into the body of the
brick allowing moisture to infiltrate the masonry.
3. Efflorescence: Deposits of soluble salts on the surface of
the masonry evident as a white haze. Moisture traveling
through the capillaries of masonry may draw excess amounts of
soluble salts along with it. As the moisture is drawn to the
surface, it evaporates leaving the salt deposits behind.
Efflorescence may be an indication that salts are present
under the masonry surface called subflorescence, which is a
more serious condition.
4. Erosion: The gradual wearing away of stone or masonry caused
by combined forces of wind and rain against the surface of the
5. Flaking: An early form of peeling or spalling where thin,
flat outer layers of the masonry become detached; usually
caused by the presence of moisture combined with freeze/thaw
cycles. Water-repellent coatings may also cause the surface
6. Peeling: May result from use of an inferior masonry unit or
from weathering (as in flaking above).
7. Rising Damp: The movement of groundwater along with salts up
through the base of masonry walls by suction or capillary
action; evident as a horizontal wet stain on the interior
and/or exterior of the building. The presence of salts can
produce efflorescence on the surface in addition to
facilitating other forms of moisture-related deterioration.
Rising damp is caused by improper drainage causing ground to
become saturated, or a high watertable.
8. Spalling: When the outer layers of the masonry begin to peel
or break off unevenly; it is usually caused by the build-up of
moisture and salts trapped in the masonry combined with the
pressures from freeze\thaw cycles. Spalling may also result
from using too hard of a repointing mortar and improper or
9. Subflorescence: A build-up of salt deposits beneath the
masonry surface as moisture in the wall evaporates. During
freeze/thaw cycles, the moisture and salts expand and build up
pressure inside the masonry. This internal pressure can lead
10. Weathering: The natural wearing away of stone or masonry due
to the combined forces of wind and rain; more commonly found
at corners and projecting details.
1. Chipping: May be caused improper repair work such as using
mortar that is too hard; may be caused by accidental damage or
2. Bricks underfired: Inferior bricks may crumble easily when
exposed to the natural weathering processes.
3. Prolonged saturaton with water caused by leaks in pipes and
gutters, open joints or ground moisture: The prolonged
presence of water in conjunction with natural freeze/thaw
cycles, can lead to spalling, efflorescence and loosened
4. Inappropriate mortar used for repointing: Mortar for use in
repointing older brick should typically contain lime rather
than portland cement. Lime-based mortar is more flexible and
can better accommodate the thermal stresses of expansion and
contraction that the masonry units undergo, while portland
cement mortar is dense and more impermeable. A mortar that is
too hard can put the units under excessive stress. When the
units expand, the dense portland cement does not compact and
can force the brick units to spall. When the units contract,
the portland cement mortar may cause cracking between the
mortar and the units, allowing water to access the masonry,
which can eventually lead to spalling of the brick units.
5. Portland cement mixture used for repointing may contain
sulfate impurities and contaminate adjacent brick with salts,
which can cause the brick to crumble or exfoliate.
6. Application of paint or water-repellent coating to masonry
surface: These coatings can prevent the transmission of water
vapor through the masonry wall which can lead to a build-up of
moisture in the units themselves. Excessive water retention
can cause efflorescence and spalling.
7. Sand-blasted brick: Sand-blasting removes the hard, outer
surface of the brick, exposing the softer, more porous core to
the weather, which can increase the rate of deterioration.
END OF SECTION