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STRUCTURAL INSPECTIONS & DEFECTS
AGE of a BUILDING - how to determine
BRICK FOUNDATIONS & WALLS
CHIMNEY INSPECTION DIAGNOSIS REPAIR
COLD POUR JOINTS, CONCRETE
COLUMNS & POSTS, DEFECTS
DISASTER BUILDING INSPECTION & REPAIR
EARTHQUAKE DAMAGED FOUNDATIONS
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
FLOOD DAMAGE TO FOUNDATIONS
FOOTING & FOUNDATION DRAINS
FOOTINGS EXPOSED, Repair Methods
FOUNDATION BULGE or LEAN MEASUREMENTS
FOUNDATION CONSTRUCTION TYPES
FOUNDATION CONTRACTORS, ENGINEERS
FOUNDATION CRACKS & DAMAGE GUIDE
FRAMING DAMAGE, INSPECTION, REPAIR
GRADING, DRAINAGE & SITE WORK
GUTTERS & DOWNSPOUTS
INSECT INFESTATION / DAMAGE
MOBILE HOMES, DOUBLEWIDES, TRAILERS
MODULAR HOME CONSTRUCTION
MOISTURE CONTROL in BUILDINGS
RETAINING WALL DESIGNS, TYPES, DAMAGE
RETAINING WALL GUARD RAILINGS
STRAW BALE CONSTRUCTION
STRUCTURAL DAMAGE PROBING
STRUCTURAL WOOD ASSESSMENT
THERMAL EXPANSION of MATERIALS
TIMBER FRAMING, ROT
WATER BARRIERS, EXTERIOR BUILDING
WATER ENTRY in BUILDINGS
WINTERIZE A BUILDING
This chapter of the "Foundation Crack Bible" discusses in detail the process of distinguishing types foundation damage due to shrinkage, expansion, or settlement, for all types of masonry foundations: concrete, masonry block, wood, stone, pre-cast. Foundation cracks and movement are discussed by type and location of foundation cracks, vertical foundation cracks, horizontal cracks, and diagonal foundation cracks, and shrinkage cracking.
Foundation cracks, which are signs of foundation damage, can mean very different things depending on the material from which a foundation is made, the location, size, and shape of the foundation crack, and other site observations.
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SHRINKAGE vs EXPANSION vs SETTLEMENT - Distinguishing Among Shrinkage, Expansion, and Settlement Cracks
Cracks will occur in masonry structures: Most solid materials may both expand and contract in response to temperature variations. Solid materials may be cracked by pressure from loading. In masonry foundations, bricks actually expand indefinitely, though probably at a decreasing rate. Poured concrete shrinks after pouring. Masonry blocks may shrink and expand.
All of these materials respond to changes in moisture and temperature. A long brick wall exposed to sunlight and cold weather and built without expansion joints will crack and fail. Concrete block walls shrink but don't normally expand (below grade). Poured concrete shrinks during curing but may also expand or contract in response to moisture.
Determining when action is needed: All cracks need to be separated into those which are expected to require no further repair except possibly cosmetic (which can help future monitoring), those which merit ongoing monitoring for change and possibly signs of worsening conditions, and those which are so significant as to require repair.
Setting priority of action: Repair work needs to be identified with respect to urgency, ranging from immediate (risk of collapse or other unsafe conditions) and less urgent.
To the extent that the inspector can see the extent of movement and the potential for damage to a building, and to the extent that the inspector can make a reasonably confident guess about the cause of foundation damage or movement, s/he can estimate the chances of its continuance and thus help set a priority for further evaluation or repair, as well as setting the specifics of outside repairs to reduce further damage such as keeping water or vehicles away from the building.
A variety of site conditions can lead to cracks in a concrete or other masonry foundation walls or floor slabs.
Speaking generally, foundations may be damaged and cracks may appear from innocent causes unlikely to affect the structure such as concrete shrinkage cracks, initial settlement, or from potentially more serious causes such as ongoing settlement, unusual pressures or loading, or from improper construction.
Identification of Shrinkage Cracks in Poured Concrete Foundations or Slabs
Shrinkage cracks in poured concrete are easily recognizable and can be distinguished from other types of cracks that occur later in the life of a foundation wall or floor slab.
Concrete shrinks as a natural process during its curing. You can see the shrinkage of even a perfect concrete floor slab with no visible cracks in its surface if it was poured inside of an existing foundation. Notice the gap between the edges of the slab and the foundation wall? Notice the stains or concrete debris on the wall at the slab level? These indicate that at the time the slab was poured it was touching the wall. A poured concrete wall shrinks as well.
Concrete curing is a chemical reaction, not just "drying" or loss of water. But depending on the concrete mix, amount of water, portland, aggregate type, temperatures, humidity, groundwater, sun exposure, groundwater, and other conditions, the amount of shrinkage that will occur in concrete as it cures varies.
In any case, this concrete shrinkage process causes the concrete to develop internal stresses. To relieve those stresses, unless control joints were included in the wall or floor slab design, the wall or floor is likely to crack in a classic "concrete shrinkage pattern" as the concrete cures.
Cracks in a poured concrete foundation which are diagonal or vertical and which are generally uniform in width, or which taper to an irregular hairline form and stop entirely, which are usually discontinuous in the crack's finest or hairline area (the crack "stops and starts" in the same area), are usually shrinkage cracks and should not be ongoing nor of structural significance, though they may invite water entry through the wall. [See our article on Using Polyurethane Foam for Foundation Repairs]
Shrinkage cracks in concrete range in length from a few inches to the entire height of the concrete wall, extending from wall top to bottom. Concrete shrinkage cracks virtually always extend through the full thickness of the foundation wall, which means they can provide a ready path for water entry into the building.
Common areas for a shrinkage concrete crack to develop are under a basement window, above a doorway in the middle of a long wall or where the foundation "steps down." Shrinkage cracks also often occur near the middle of a large poured concrete wall [or floor] if no control joints were used. [Concrete control joints are very often omitted in residential construction. Shrinkage cracks and how to recognize and diagnose them are discussed further at SHRINKAGE vs EXPANSION vs SETTLEMENT.
Brick, in particular, whether used in a foundation or as a building wall, expands over time and as moisture, temperature, and other conditions vary. Dave Wickersheimer, P.E. and R.A., who is a masonry failures expert from the SHC, informs us that brick "grows" or expands indefinitely. However if we exclude heating effects of sun exposure (discussed below), most brick expansion from its internal chemistry probably occurs early in its life.
Thermal expansion of brick: Thermal expansion cracks in brick are often nearly vertical, maybe passing right through the bricks not just at the mortar joints, and tend to be near the building corners.
In any long brick wall, whether it's veneer or structural, if it's real brick, look for expansion cracks if the wall design did not include vertical expansion joints. Southern exposure, walls exposed to more sun, take more heat and may show more expansion due to the added thermal effects of sunshine.
Although it's natural state causes brick to expand or "grow" slowly in size continuously, more often, brick walls exposed above-grade are subject to more rapid and more significant heating gains from sunlight.
These brick walls may expand (when heated) and contract (when cooled) sufficiently to cause major damage if proper control joints are not used during construction. If you observe long expanses of brick masonry walls above grade and without expansion joints, look for expansion cracking. When caused by thermal expansion, brick walls may show most movement at the two ends of the wall most-exposed to sunlight.
The author, using a simple plumb line and measuring tape, has measured as much as 4" of expansion found at the top of a brick structure whose wall corners leaned out 4" over the wall bottom from this force over the height of a two story structural brick wall.
Brick masonry walls below-grade are of course not exposed to heating and expansion from sunlight, but instead are exposed to earth pressure (look for horizontal cracking), moisture gain, and in freezing climates, frost damage too. Look for horizontal cracks in brick walls at or near the frost line, and look for stair-stepped cracks at corners of the building from frost heave or settlement.
We discuss and illustrate thermal expansion of brick walls in detail at Thermal Expansion Cracking of Brick.
The photograph shows a significant settlement crack in a poured concrete foundation of a new (modular) home. This crack appeared first as a fine hairline crack. The owner monitored the crack as it expanded to a significant width over the ensuing year.
A combination of poor site preparation of soils below the building footings (un compacted fill), portions of footings sitting on bedrock, and nearby blasting led to differential settlement that produced this damage. We suspected that also some reinforcing steel may have been omitted from construction of the foundation wall.
A settlement crack is more likely to be wider at top than its bottom as the foundation "bends" over a single point (or as one section of footing tips downward from its neighbor), allowing differential settlement; it is possible for a settlement crack to appear fairly uniform however if a foundation breaks vertically and then pursues differential settlement.
Settlement cracks need to be separated into initial settlement due to construction or site factors and ongoing settlement due to site factors.
Settlement cracks are usually wider at the top of the crack, usually continuous, and may occur multiple times in a wall
Watch out: To be used properly, this information must be combined with specific on-site observations at the particular building in order to form a reliable opinion about the condition of that building's foundation. Anyone having concern regarding the structural stability, safety, or damage of a building, foundation or other components, should consult a qualified expert. [The photograph shows severe foundation damage discovered during construction of a new home.]
Repair of Foundation Cracks
For detailed information about foundation repair methods, including repairs to various kinds of cracks in concrete, see:
Continue reading at FOUNDATION DAMAGE SEVERITY or select a topic from the More Reading links shown below.
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