Homeowners or property investors don’t want to experience a double-whamming fiasco after purchasing their dream house. No investor or property owner likes to see surprises like cracks in the walls, slopes like a circus tent on the floor, doors and windows not closing properly, humps in the garage floor, and bumps in the basement walls. Such problems as you wouldn’t believe existed long before you bought the property, few are visible to the naked eye, and while many of these problems are hidden in hindsight.
These ordeals are not exaggerated in any way, it’s what happens every time. About half of the houses built every year in the US and Canada are founded on expansive clays. Of these, about half eventually will show some form of distress. This indicates that one in four would have clay trouble, which leaves 25 percent of the homes with expansive soil problems to become seriously afflicted, and as time passes, it reduces the chance to about 5 percent, accounting for major difficulties that eventually resulted in double-whamming expenses. The 5 percent of troubles inherited may cause the homeowners or property investors to incur a repair cost from 10 to 50 percent or more of the value of the house.
Let’s say you are a newbie in buying property, how do you recognize that there may be problems from the property such as expansive clays. The most important clue to look out for is wall cracks, particularly at corners of doorways and windows where stresses predominantly concentrate. But remember, wall cracks can be made to disappear under paint and patch, but with an expansive clay problem, they soon will be visible.
Nonetheless, a new house buyer is not exempted from the nightmare, of course, in a new house some cracking can be expected for reasons other than clay expansion. Whenever a new foundation settles, the walls can shrink a bit on drying. So the tendency for cracks becomes a reality after this, which keeps coming back and getting bigger with time if not checked and would soon cause serious problems.
The ground movement caused by clay expansion is cyclical and sideways and depends on the weather. This process continues while damages keep accumulating. Clay shrinkage can occur after lowering the groundwater table, resulting in losses of water, an increase in load from loss of buoyancy. One procedure is to measure elevations of several points on the house every month to ensure you have leverage before the damage becomes unbearable.
During the dry seasons, shrinkage opens vertical ground cracks that fill with debris filtering in from above, which in turn keeps the cracks from closing when wet weather returns and the clay expands. So the repeated cycles of these conditions compress the clay laterally, and eventually build pressures sufficient to push in walls and typically develop horizontal cracks along mortar joints at about the outdoor ground level.
Strong wind by a tornado can have subtle impacts on expansive clay. Whenever a tornado hits, it causes air pressure to be quickly lowered so the air inside a house expands and lifts the house up, and sometimes detaches the entire building from the foundation. Houses bolted to their foundations are exempted during this tornado hit. A temporary reduction in weight on the foundation can allow a concrete block basement wall to crack. After the wall yields and cracks, it doesn’t move back to its original state because of the difficulty of pushing the soil back due to passive pressure.
✓ Check and look at the ground for clues relative to expansive clays. One such clue that suggests this is shrinkage cracks.
✓ Look up at structures for other clues to expansive clays. Important clues are wall cracks, tilted floors, sticking doors and windows, attempts at repairs, and nervous real-estate agents.
✓ If there is a hint that there might be an expansive clay problem, call on an expert, usually, an expert who specializes in foundation repair.
✓ Where a slab-on-grade is used, the availability of water to the soil underneath the house can be reduced by using a moisture barrier around the house, for example, a sidewalk that is tilted outward for better drainage. A vertical barrier also can be used, a heavy layer of plastic sheet in a narrow trench, or a trench that is backfilled with concrete or hydrated lime.
✓ Roof water also should be taken some distance away from the house. Underground tile drains take away free water, but not water that is held in soil capillaries or within the clay. Such drains, therefore, are not very effective at preventing expansion, although by preventing a good soaking they can help the expansion to occur more evenly.
Sometimes a ground crack will run back under a slab-on-grade foundation and create a strange kind of reaction, splitting the house in two, like continents adrift. A sand layer that was spread prior to pouring the concrete floor is the culprit because it sifts down into the ground crack and keeps it from closing. A wet-dry cycle episode opens the house further with time.
Where the trouble runs deep, vertical piles or shafts can be set in the ground to support a structure from underlying stable soil. The piles need not extend all the way through the clay, only below the depth of the seasonal changes in moisture content. Concrete shaft foundations can be made by drilling holes and filling them with concrete, then inserting steel rods to keep the shafts from being broken when clay around them expands and tries to pull them up. Sometimes the bottom of the hole is reamed out oversize with grooves or an inverted cone or “bell” to create an anchor.
It is noteworthy that where deep foundations are used, the tops should be connected to the horizontal grade beams that will in turn support the floor and walls. Because clay between the shafts can still expand and lift up the grade beams.
An approach that gets mixed reviews involves anchoring basement walls to the soil with “tiebacks.” Horizontal holes are drilled every 4 feet or so through the wall, and long bolts are run out to steel plates or other anchorage embedded in the soil. The tightened bolts compress the clay between the deadmen and the wall, reducing clay expansion.
Diversion of water away from the wall also is a must, to help resist forces that would otherwise cause the wall to lean, when a seawall is pushed after heavy rain.
If an interior basement wall is going up while the rest of the structure stays calm, the least expensive correction may be to take off the top of the wall and substitute a row of small screw jacks to let the house down a little at a time. Lowering should be no faster than 1/4 inch per week to keep the noise level low and allow the plaster to adjust.
A slurry of hydrated lime in water sometimes is injected under pressure to stabilize expansive clay, one problem being to get enough time to do the job. Another approach is to introduce quicklime in boreholes made in the soil along and under a foundation. Typically 4-inch holes are drilled on 2-foot centers all around the outside walls, with every other hole, slanted to go back under the foundation.
Holes should be extended through the depth of the active shrink-swell zone and will create a vertical zone that any laterally flowing water must penetrate to get to untreated soil.
✓ When it comes to clays and their influence on building foundations, floors, walls, and pavements, expansive means expensive, particularly if the problem is not taken into account during construction.
✓ Three approaches are to replace the clay with something better, try and live with it, or treat it with lime so it becomes nonexpansive. Living with expansive clay means controlling the access to water, and using structural slab-on-grade foundations that can bridge between high spots, or deep foundations to support grade beams and structural floors.
✓ Basement walls can be protected by cutting the soil out at an angle so pushing is directed upward instead of flat against the wall.
✓ Repairs can involve in-situ lime stabilization, and the use of jacks to let down high places.
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Water gets into the foundation of a building in different ways, of these, the most common factors are not having effective foundation drain tile installed, infiltration and condensation, cracks in walls, poorly designed window well, improper grading, leaky joints between structural elements and cracks in slab
