Houses have thousands of parts, typically including 60 cubic yards of concrete, 10,000 board feet of lumber, and 300 pounds of nails and screws. At first it all fits seamlessly. But as houses settle and furnaces kick in, cracks appear. Most of them are cosmetic, though some indicate structural problems, while others defy repair and open year after year.
Structural foundation faults.
Many concrete foundations sprout short, hairline cracks. But they are skin deep and rarely indicate structural problems. Even most larger cracks are benign — simply the one-time result of modest, initial settling when the house is new. Longer, deeper, actively expanding cracks, however, are serious business.
Here's the difference. Old, stable cracks are weathered. Under a bright light, the crevices are dirty, and may contain bits of leaves, spider web, or other debris. Conversely, the crevices of new, unstable cracks are usually clean, and the masonry inside is a different shade. If a crack could be active, it's wise to track its movement. For example, if you notice that isolated cracks in a block wall begin to join up in a staircase pattern, the foundation could require extensive repairs. . Clean the wall, tape on a piece a tracing paper, and draw an exact map of the cracks underneath. Mark the corners where your tracing rests on the wall, and later you can reposition it to see if anything has changed.
Patching stable cracks in masonry.
On dry cracks, scrape out any loose material, brush the crack clear of dust, spritz in some water (or concrete bonding agent on large faults), then force in cement and smooth. On wet cracks (though foundation leaks are best stopped outside), use hydraulic cement.
Cracks in gypsum drywall.
If the frame was wet during construction, or underbuilt, or poorly connected, it can move enough to pop nails and disrupt drywall joints. If you're building a new house or addition, it helps to use stable timber (stamped on each board no more than 19 percent moisture content), and to build deeper beams. For example, where a beam made of 2-by-8s meets code at a passageway between rooms, use 2-by-10s instead.
Patching problem drywall.