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Historic Preservation - Technical Procedures

Spectitle:

Historic (Early) Brick: Characteristics, Uses And Problems

Procedure code:

0421108S

Source:

Hspg Prepared For Nps - Sero

Division:

Masonry

Section:

Brick Unit Masonry

Last Modified:

07/31/2013

Details:

Historic (Early) Brick: Characteristics, Uses And Problems


Historic or Early BRICK:  CHARACTERISTICS, USES AND PROBLEMS


This standard includes general information on the characteristics
and common uses of historic or early brick and identifies typical problems
associated with the brick along with common causes of its
deterioration.  Historic or early brick, from 18th and 19th centuries or earlier, were not hard fired throughout resulting in a hard outer crust and softer center.


INTRODUCTION

Characteristics of Brick:

-    Soft

-    Porous

-    Outer crust is harder and more dense than the inner material

-    Fireproof

-    Long life when properly maintained

-    Low maintenance when properly laid

-    Found in wide rage of colors and textures

-    May be cast in decorative molds

-    May be carved

-    Bricks made 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
    accepted maximum).

-    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 historic ones.


TYPICAL USES

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, sawn, or rubbed; may be used in
    a variety of colors, textures, bonds and joints.

-    May be covered by other finish materials such as stucco,
    plaster or paint, or may be exposed both on the interior and
    exterior.


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
induced problems.

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
routinely.  


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
    materials.

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, a condition called subflorescence, which is 
    more serious.  Water infiltration caused by rising damp, deterioriated mortar joints, and other building envelope failures may also be evident in         surface efflorescence.

4.   Erosion:  The gradual wearing away of stone or masonry caused
    by combined forces of wind and rain against the surface of the
    material.  

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
    to flake.

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
    abrasive cleaning.

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
    to spalling.

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.


HUMAN-INDUCED PROBLEMS

1.   Chipping:  May be caused improper repair work such as using
    mortar that is too hard; may be caused by accidental damage or
    vandalism.

2.   Bricks underfired:  Inferior bricks may crumble easily when
    exposed to the natural weathering processes.

3.   Prolonged saturation with water caused failures in the roof or flashing above or 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
    mortar joints.

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, hard, inflexible, and more impermeable.  A mortar that is
    too hard can put the units under excessive stress.  When the
    brick units expand, such as when heated by the sun, the dense portland cement does not compact and
    can force the softer and more porous 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
 


early brick, historic brick, 18th century brick, 19th century brick, underfired brick, underburned brick