There are no perfect houses and that would include its foundation. Whether you have a new home or one that’s a hundred years old, house foundations crack. Houses shift and settle after construction. Houses will have cracks in either the cosmetic finishes or structural components. Most of these cracks have no structural significance. The common types of cracks in foundation walls will include;
Vertical (or near vertical) cracks; Just because a wall has cracked doesn’t mean that it has failed or that corrective action is required. If the crack is narrow (1/8 inch or less), is nearly vertical, has no lateral separation between the adjacent portions of the wall, and no water is leaking through the crack, no action generally is required. This is a shrinkage crack and occurs as moisture in the wall evaporates causing the wall to shrink into the voids created by the escaping water. This type of crack is controlled, or minimized but not eliminated by, using horizontal reinforcement steel, which helps distribute the stresses in the wall. If horizontal steel is present, you are more likely to get several very small cracks instead of one or two much wider cracks. Another method of limiting shrinkage cracks is to control the amount of water used in the concrete mix.
Reentrant Cracks; Whenever a concrete element has a sharp angle, there is a concentration of stress. This almost always results in a crack called a reentrant crack that emanates from the inside corner. It may be vertical, horizontal, or diagonal as it exits the corner. This phenomenon exists in nearly all materials. Round openings can dissipate the stress but this is not practical in concrete wall construction. The typical remedy to reduce this type of crack is the placement of steel reinforcement in the corners. It will not eliminate these crack but keep they tight and controlled.
Horizontal cracks; Horizontal cracks require greater scrutiny. Most residential foundation walls are designed to span from the footing or floor slab to the connection of the floor structure above. An 8-inch concrete wall in normal soil conditions usually is strong enough to withstand the forces exerted on the wall with no vertical reinforcement. Exceptions include areas with high ground water conditions or in expansive soil conditions. If there is vertical reinforcement in the wall, a horizontal crack is probably not a concern. An expert should be consulted when a horizontal crack appears to evaluate whether there is a structural risk.
These cracks typically result from one or more of the following;
1. Soil settlement beneath the footing resulting in downward movement of the footing, and shifting is common to most newly constructed homes.
2. Alteration of the local water table whenever a new home is built. Specifically, the soil beneath the home dries; the resultant soil shrinkage causes minor settlement of the footing which can result in hairline cracking in the foundation walls.
3. A new home, without of furniture and effects, does not impose a significant load on the foundation. Once all of your furniture and appliances are moved in, the weight borne by the foundation, and the structure in general, increases and causes some flexing (or movement) of structural members throughout the building. This increased load can cause hairline cracks in the foundation.
4. Drying shrinkage. While poured concrete is dries and hardens, it will shrink. The major factor influencing drying shrinkage is the total water content of the concrete. As the water content in poured concrete increases, the amount of shrinkage increases. Significant increases in the sand content and significant reductions in the size of the coarse aggregate used in poured concrete increase shrinkage because total water content is increased and smaller size coarse aggregate provide less internal resistance to shrinkage.
5. Thermal expansion and contraction of concrete. Concrete poured during high daytime temperatures will contract as it cools during the night, this can be sufficient enough to cause cracking if the concrete is restrained.
6. Restraint; The restriction of free movement of fresh or hardened concrete subsequent to the completion of placing (pouring of concrete) in formwork or within an otherwise confined space; restraint can be internal or external and may act in one or more directions.
7. Subgrade settlement or movement. The dropping of soil or the footing due to their mass, the loads imposed on them, or shrinkage or displacement of the underlying support.
Most foundation cracks are minor and insignificant; they are common to both poured concrete and block foundations. Structural cracks (horizontal) in residential foundations are usually the result of settlement and/or horizontal loading. They can be the result of hydrostatic pressure or the use of heavy equipment next to the foundation. The possible implication of cracks in your foundation is moisture penetration, moisture that can ruin finished wall coverings, floor coverings and furniture.
Water will leak through a foundation crack if there is enough hydrostatic pressure to force water through the crack. If a waterproofing system was installed during construction, the basement may not leak even if there is a large crack. Keep in mind that waterproofing is not the same as damp-proofing. Installing an exterior waterproofing system after the wall has been backfilled can be cost prohibitive. The best solution is the use of an epoxy injection system. It will adhere to the side of the cracks and actually may strengthen the wall. These systems can be DIY but is it highly recommended that they be applied by a professional.
If you take anything away from this article…take this. All foundations crack, your foundation, my foundation and most of these cracks are insignificant and have no structural implications. If you do have a concern about the size and type of crack call a professional to evaluate.
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Source by Rick Deckert
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