Causes of Cracking, Shifting, Bending or Bowing Walls
This section will talk about some of the most common causes of wall cracking, bending, bowing and shifting.
Water pressure is one of the most common causes for cracking and bowing concrete. It can push upwards (in what's known as hydrostatic pressure), or push laterally against a wall, especially in colder climates.
In colder areas, moisture freezes when it gets cold (and we all know that water expands when it freezes). If there's enough water in the ground, that freezing process puts pressure on the wall - often enough pressure to crack the wall. Once it's cracked, it can now begin to move with changes in the seasons.
Notice the lack of gutters & downspouts on this house
What can put too much water in the ground? Bad or malfunctioning gutters or downspouts; a high water table, broken pipes or lines in the street or yard; dense clay that holds water, or just an area with a lot of rainfall!
Trees and some bushes can grow roots that exert huge pressures on foundation walls, whether it be a crawlspace or basement. Keep in mind that tree roots can grow as far away from the tree as the tree is tall - so that tall oak tree in your yard might very well have roots that extend to the basement walls.
Notice the proximity of the tree to the left corner of this house
Poor Building Process
There's no other way to say this - it's possible for the mason to be in a hurry, or build a wall when conditions are not adequate. He might not prepare adequately for the conditions he's working in. He may throw lots of junk in the trench by the walls as it's being built, and that can create issues later on. He may put the wrong size sill plate on the wall, creating lateral pressure on the wall. or he might backfill too soon after building the wall, while the concrete is still curing.
There's a myriad of things that can go wrong in the building process - and the result of any of these issues is that the wall cracks or begins to bow.
A new construction that already needs foundation stabilization
Time breaks down just about everything. We know, you're shocked, but it's true. The fact is, basement structures probably only last a hundred years or so, and then they need replaced - and that's if no other outside factors are involved. Add settling, shifting, expansive soils, and outside pressures, and you can cut that number down considerably.
The point here - nothing lasts forever.
Footers (the things your foundation sits on) may be built on loose material. It might expand or contract over time because of the weight on it, or you may be in an area with soils that move. In any case, settling results from the shifting. What you'll see is cracks that develop from that settling.
Loose backfill that has been placed around the house can also settle and exert extra pressure on the walls, creating the same problem, especially if that backfill is comprised of lots of dense clay materials.
People expect their roofs to need replacing periodically. They also expect to re-paint or re-side their home periodically. What they don't realize is that the same thing applies to a foundation. The coatings put on the walls can break down over time, allowing water to come in contact with the concrete. Once that happens, the water begins to affect the strength of the concrete. At that point you might begin to see discolorations, water, cracks, or even bowing of the walls.
Shrinkage comes from the curing of the concrete or mortar. As it shrinks, cracks develop, usually along mortar lines, but sometimes in the form of vertical cracks. Once there is a crack it is weaker than the surrounding wall, and that leads to the possibility that pressures from outside will begin to bow that wall.
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