Speaking from experience, major cracks in a foundation are a concern to a homeowner. Neglecting your home's foundation does not help the situation. But, there are remedies that will lessen your worry about your home's cracked foundation. Minor cracks in a foundation are concerning and should be properly assessed. But, major cracks are a sign of movement in the foundation and they should be inspected by a licensed contractor and fixed. Filling in the cracks and preventing them from spreading is what you need to do. Don't ignore the cracks. Instead, fix them to prevent further structural damage. If you have a concrete slab with cracks that are more than 1/4 inch wide, call a structural or civil engineer to review the damage, find the source, and provide a solution to the problem. For more severe damage, you may need to consult with soil engineer to find the reason for the shifting and cracking and fix the problem.
In harsh climate where there is severely cold winter weather, foundations will shift and move which leads to minor cracking. Even in milder climates, concrete moves an inch or two sometimes resulting in minor cracks. During hot weather, concrete expands and then shrinks when the weather turns cold. Cracks in foundations can be caused by water, shifting soil, or tree roots that spread into a foundation and deteriorate. Before a minor crack turns into a major one, repair them to prevent further damage.
Before you fix the cracks, prepare the surface. To fix cracks, choose a concrete patching product that has some elasticity. A vinyl concrete patching product is good for repairing cracks that are over 1/8 inch wide. If a vinyl concrete patch material cannot be found, use a mixture of one part Portland cement to three parts sand. Add enough concrete bonding agent to the mixture until it is similar to the consistency of slightly stiff mashed potatoes. Then, take a small portion of the stiff mixture and add more of the bonding agent and mix it until it becomes somewhat soupy. Use an old paintbrush to brush the soupy material into the crack. Use a metal trowel to pack in the stiff mixture. Once you have filled the crack, use the trowel to smooth out the surface. Latex caulk containing silicone or polyurethane caulk can be used to fill minor cracks. Use a caulking gun to push the caulk into the crack. Caulking products provide elasticity and are pliable allowing for expansion and contraction. Most caulking products are self-leveling and do not need to be smoothed over with a trowel. To finish the repair task, use water to lightly spray the patch twice a day for about a week. This will prevent cracking and to help it to cure. Allowing the repaired surface to cure is an important part of the process. Be patient and allow time for the curing process to complete. In addition, consider using a quality concrete sealant to repel water and prevent moisture. The sealant will protect the repaired surface.