Stairstep cracks in masonry joints are usually caused by a plugged gutter or some other moisture problem that is exerting pressure on the wall.
A floor that’s not level is one tip of a possible foundation problem. Some people can sense this easily; others never notice even when a floor sags a couple of inches.
If you’re in the latter group, there are other ways to hear your house whispering that the foundation is rising or sinking unevenly: A door begins to jam or fails to latch; cracks appear in walls, especially over doorways or windows or where walls meet ceilings; cracks open in vinyl or ceramic tile over a concrete floor. Windows that fail to budge or to close completely also hint at foundation problems, assuming the culprit isn’t just sloppy or sticky paint or rotten wood frames.
Slab foundation problems
ull set of drawings for an engineered solution.
If it’s a structural problem, your foundation is settling unevenly and has the potential to skew or pull apart the framing unless you take action. Best case: You can get the house level again just by keeping soil near the house evenly moist, either by irrigating during dry weather if you live in a damp climate or by switching to landscaping that doesn’t need irrigating if you live where it’s usually dry.
Worst case: You need to underpin the foundation with helical screws or concrete piers. Installation costs $1,200-$1,500 per pier, with one every 6 to 8 feet.
Outside, take the long view
Moving outside, check to see if your foundation is straight by sighting down the length of your foundation wall from each corner. You should see a straight line. A bulge or divot in either a block foundation or a poured concrete wall could signal that the foundation has shifted.
Check for leaning walls with a level. If the top of the foundation sticks out beyond the walls in one area, the foundation wall may have tipped. Any signs of shifting or bowing means that the soil may be expanding and contracting, putting pressure on foundation walls, and remedial steps are necessary.
The poke test
If your house has a poured perimeter foundation and it appears to be shedding sand, poke it in a few places with a sturdy screwdriver. The concrete should be so dense and hard that you do no damage. If you can excavate a hole, the concrete could be deteriorating because the mix contained dirty or salty sand, or too much water. This problem, common in homes built in the early 1900s in some parts of the country, has no remedy short of a new foundation, perhaps a $35,000 prospect.
Checking crawl spaces
In the basement or crawl space, look for foundation problems that may include a system of posts and concrete supports, or piers. Posts should stand straight and be firmly planted underneath the beams they support. Bottoms of posts should rest firmly on concrete piers.
You shouldn’t find puddles or see framing that’s wet. Check for rot by probing wood posts with a screwdriver or awl.
Puddles and other signs of moisture in a crawl space may indicate poor drainage around the perimeter foundation. Be sure that gutters aren’t plugged, and that soil slopes away from the foundation at the rate of 6 inches for every 10 horizontal feet.
As concrete cures, it shrinks slightly. Where the concrete can’t shrink evenly, it tends to crack. Cracks where there is an L-shape section, such as where a foundation stairsteps down to follow a hillside, are probably shrinkage cracks, especially if they meander and taper down to a hairline. These aren’t a structural issue, though you might need to plug them to keep the basement or crawl space dry. Hairline cracks in the mortar between concrete blocks are also rarely worth worrying about.
If you find small cracks (less than 1/16-inch wide), paint over them with a concrete waterproofing paint (about $25 a gallon). Then check periodically to see whether the paint has cracked, which means the gap is opening up under pressure.
Stairstep cracks in masonry joints are a bigger concern, especially if the wall is bulging or the crack is wider than ¼ inch. A plugged gutter or other moisture problem outside is probably exerting pressure on that part of the wall. You’ll need a structural engineer to help identify a cure, which can include bolting on steel braces ($500-$700 each, often spaced about 6 feet apart along the wall) or using epoxy to glue on straps of carbon-fiber mesh ($350-$450 each, similarly spaced).
Horizontal cracks are most serious, and indicate that water-saturated soil outside froze and expanded, pushing in and breaking the foundation. Perhaps gutters backed up and heat was off for an extended period during especially cold weather. The consequence: You probably need a whole new foundation.
Horizontal cracks also occur because of problems with underlying soil. If you have soil that expands when damp and shrinks when dry, you face the same range of solutions as if you had a slab foundation. Hire a structural engineer to help you sort out your options.
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