Once it's clear that the foundation has some problems and needs to be fixed, there are two things to think about. First is solving immediate problem and second is to solve the actual problem. Before we move forward, if you haven't read the 'Foundation Problems - Warning Sign' blog, please do so as that explains what to look for in foundation problems.
FIX THE IMMEDIATE PROBLEM
If the cracks are less than 1/16 inch wide, paint over them with a concrete waterproofing paint. Then check periodically to see if the paint has cracked. If so, that means the gap is opening up under pressure and the actual problem has not been resolved.
Injecting Epoxy ($1,500-$3,000)
If cracks are wider than ¼ inch wide or stair step cracks in blocks, one can inject epoxy/ epoxy putty and then fix the actual problem that caused it.
If the foundation is uneven and has bowed or severely cracked, it requires substantial reinforcement to prevent further damage. In this case, repair it by using wood or steel braces or wall anchors spaced 6 feet apart along the entire wall from the inside.
Wood and steel braces are installed against the wall and attached to the floor and overhead joists. This stops further movement but intrudes into the basement for about 6 inches. ($600 - $800 each)·
Wall anchors consists of metal plates (6-8 feet apart) on the inside and outside of the foundation wall. These plates are connected by horizontal steel rods. The connectors are then gradually tightened to stabilize and straighten the wall. ($500 - $700 each)
Epoxy with Carbon Fiber mesh
Another option to consider would be spreading epoxy in vertical strips and then pressing on carbon-fiber mesh to lock the wall in place. ($350 - $500 each)
Rebuild foundation ($15,000 to $40,000)
If the foundation walls are caved in more than 3 inches or has a horizontal crack, it probably is not possible to fix the problem from inside. In this case, one will have to excavate from exterior and rebuild the foundation wall.
FIX THE ACTUAL PROBLEM
We also need to address the actual problem that let to foundation issues. The most common cause is water accumulating in the soil near the foundation wall which leads to expansion of the soil putting pressure on foundation walls/footings. This expansion and contraction over time leads to cracks.
There are couple of things to look for to make sure water doesn’t get accumulated in the soil near foundation wall:
Gutters and downspout are working appropriately. They are not plugged.
Make sure the soil around the foundation is properly graded away from the foundation – ideally it should slope minimum of 6 inches for every 10 horizontal feet.
Perimeter drain system (e.g. French drain) is working appropriately (not clogged) and channeling sub-surface water away from the foundation.
Hose bib should tighten properly and not be dripping/leaky. Also check for any broken pipes in the near vicinity.
This case study flip property had all these issues - Gutters and downspout not installed properly; leaky hose bib, negative gradation along with no perimeter drain system.
Once the actual problem and immediate problem is taken care of, the job is not yet done. Keep monitoring the foundation wall periodically to make the cracks don’t widen or doesn’t show any other form of stress. If they do, the actual problem is not yet resolved.
Foundation repair can be tricky and is always highly encouraged to have a structural engineer take a look at it and provide his professional recommendation. Expect to pay about $500 for a structural inspection and about $2,000 to $3,000 if a full set of engineered solution is required.