Concrete slabs and foundations typically become damaged due to a poorly prepared undersurface and water penetration. If the soil or subsurface of the concrete slab is not properly compacted, the soil can move and cause cracks or breaks in the surface. Water penetrating under the concrete can also cause the slab or foundation to move. Repairs to some concrete faults can be accomplished by the homeowner. Larger problems may entail the services of a contractor with specialized equipment.
Small Cracks in Slabs
Cracks that do not cause the surface of the slab to move appreciably can be repaired by the homeowner. The crack is chiseled out wider at the bottom of the crack than at the top. The crack is kept wet for a 24-hour period. A slurry of concrete mix is wiped on the walls of the crack and a heavier paste-like mix is poured into the cavity. The repair is kept moist and covered with plastic for a five to seven day period. This allows the repair to slowly cure.
Large Cracks and Uneven Slabs
This type of damage to a slab is generally related to the undersurface of the slab settling or washing away. Typically, the removal of the slab is performed, a new bed of gravel is laid and a fresh slab is poured.
A technique of "slab jacking" is being used to repair uneven slabs. Hole are cut into the slab in areas that need to be raised. The cores are carefully removed to be used later. A wet mix of concrete is pumped under the slab through the holes. As the pressurized concrete fills the void, the slab is raised or jacked into place. The plugs that were removed are replaced into the holes with a concrete adhesive. Linear cracks in the slab are repaired as described above. The slabs can be walked on immediately, while heavier duty traffic must be withheld until all the concrete cures. The typical cure time for this type of repair is three to seven days.
Foundations that experience drastic settling or water washout can be fixed by installing metal ground jacks. Deep holes are drilled into the ground. These holes can range from 10 feet to 50 feet in depth. Metal pipes or jacks are then placed into the holes. Plates made of angle iron are permanently secured to the damaged foundation. Powerful hydraulic jacks raise the foundation to the correct level. The pipes are cut to length and welded into place on the angle iron. Proper drainage trenches must then be installed alongside the foundation walls to remove any settling water. This type of repair can be very costly, but may be cheaper than jacking the house up and replacing the entire foundation..