At best, the crack is just a shrinkage crack caused by the curing of concrete when it dried during the original construction. Shrinkage cracks are generally hairline cracks that propagate and ends just as abruptly anywhere on the foundation. Shrinkage cracks can usually be repaired easily and cheaply using cosmetic repairs.
Another common cause of cracks in the foundation is settlement. This happens when a newly constructed house settles into the ground itâ€™s built upon. Sometimes the house settles uniformly and in this case the stresses on the house as well as the propagation of cracks are usually minimal. Other times though, different areas of the house settle at different rates producing substantial cracks on the foundations. This is a dangerous situation, especially if the settlement is ongoing, as the structural stability of the house is at risk. Settlement cracks are usually fixed by going after the root of the problem, which in this case is finding solid ground for the house foundations to rest on as well as fixing structural damages on the foundation.
Foundation cracks can also result from earth, water or vehicle loading. Put simply, saturated earth, water or heavy object near the foundations can introduce stresses that may cause it to crack. Some common symptoms of this type of foundation problem are water intrusion in your crawlspace or basement as well as horizontal cracks along the top half of the perimeter foundation or basement wall. Usual repairs involve waterproofing and drainage installation.
Last but not the least of common foundation crack causes is seismic activity. Cracks of this type can be cosmetic or structural. Because of the potentially serious structural implications of cracks in the house foundations, itâ€™s best to have a qualified professional do the assessment and repairs. If you want to read more about foundation cracks, here are some blog posts that might help:
Factors Considered when Evaluating Concrete Cracks: http://www.sinaiconstruction.net/LA-foundation-retrofit-blog
Basement or Perimeter Foundation Concrete Cracks: http://www.sinaiconstruction.net/LA-foundation-retrofit-blog
Concrete Cracks Caused by Settlement: http://www.sinaiconstruction.net/LA-foundation-retrofit-blog
Concrete Cracks Caused by Shrinkage: http://www.sinaiconstruction.net/LA-foundation-retrofit-blog
Overall structure settlement (a house can settle for decades)
"Differential' settlement ( one portion of the house has settled at a different rate, common when additions are built on).
Soil conditions such as expansion/contraction and heaving which can damage a foundation.
Poorly constructed foundation (improper excavation, etc.)
Footings: may crack from pressure exerted by adjacent soil, water infiltration or improper construction. This is common in SF homes on hillsides. In addition, many SF homes were built using sand that had salt in it. This caused the concrete to deteriorate over time.
These are the more common causes, but not all. Best to have an engineer examine.
Many time cracks do not need repair, they just need monitoring to see if they are growing.
To repair a foundation the weight of the structure is removed from the foundation and the defective part is torn out. A new foundation is built and tied into the existing foundation using steel reinforcing bar and very strong epoxy glues.
If you have concerns hire a structural engineer to inspect the property.
Pressure on exerted on those walls from the outside from soil expansion (when it rains or snows, the ground gets soaked. If it doesn't drain properly, the soil will swell, putting more pressure on the outer wall of your home's foundation).
This is when small cracks develop on the outside, allowing water to seep in. As the cracks grow, more water enters and it weakens the cinder block, concrete or stone that makes up your foundation.
Soon, the inside walls will show cracks.
When you see these, yo0u'll start to see moisture, water, dampness and possibly mold. All of which are symptoms that the basement has a huge problem.
If this is the cause, an epoxy seal will do almost nothing, especially long term as the cracks grow and begin to separate.
Ask your contractor if they use a steel plate in addition to any sealants. This will help keep the walls from coming apart further. And, they have to address the problem of water in the walls and the pressure from the outside.
For more info on this, check out this link :
What did you learn about your cracked foundation?
How big is big? Is it offsetting or level? Is it new or old? Does water come through it?
There are many products that can be used as concrete sealers, but preparation is often key to a lasting finish.
Some cracking of the foundation is pretty normal in almost all homes. This is mainly from curing and initial settlement. Also since you live in a seismic area depending on the age and location of the home it could be from an event.
How the crack looks and if there are other indicators in the home that may be indication of a more severe issue. A good contractor or home inspector may be the best way to see if you need an structural engineer.
Also you can set up some markers on the foundation to see if there is active movement.
This repair may not even be necessary, or it may require major expense. You could start off with a contractor inspection and see if they recommend a structural engineer to look, or you could just hire and engineer. The engineer's reports are generally much more expensive so keep that in mind
There are all kinds of cracks. Some are hairline cracks and most are caused by settling.
I had an inspection done on a 2-unit building that I sold in Corona Heights. The inspector discovered a huge crack and recommended that a structural engineer look at it. We hired one for about $600. He looked at the crack--this was in the garage floor--and said that it probably happened soon after the concrete had been poured (60 years or so ago) and that since there was no "movement", the foundation was fine.
So you should get a structural engineer to look at it first and she or he can recommend the appropriate repairs that might need to be done.
I can recommend two structural engineers if you need a referral.
It could come from a number of problems. It usually means there is a water intrusion issue somewhere. You should consult with a licensed contractor that specializes in foundations or concrete work. Here is a really informative video http://www.youtube.com/watch?v=-FP6nKvYT5A. After you get past the first few minutes it information is valuable.
I hope this helps!