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
deterioration.


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

-    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
     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 old 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; 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
     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 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
     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 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
     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 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