Historic (Early) Brick: Characteristics, Uses And Problems
- Procedure code:
- Hspg Prepared For Nps - Sero
- Brick Unit Masonry
- Last Modified:
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.
Characteristics of Brick:
- Outer crust is harder and more dense than the inner material
- 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 theend 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 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 materials 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
- 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.
- 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.
- 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.
- Erosion: The gradual wearing away of stone or masonry caused by combined forces of wind and rain against the surface of the material.
- 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.
- Peeling: May result from use of an inferior masonry unit or from weathering (as in flaking above).
- Rising Damp: The movement of groundwater along with salts up mthrough 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.
- 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.
- 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.
- 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.
- Chipping: May be caused improper repair work such as using mortar that is too hard; may be caused by accidental damage or vandalism.
- Bricks underfired: Inferior bricks may crumble easily when exposed to the natural weathering processes.
- 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.
- 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.
- 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.
- 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.
- 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.