Concrete patios, like any other concrete slab, can sink from changes in its base. Whether the base shrinks or sinks from shifting soil, natural settling or erosion by running water, sections of your patio—and even the entire slab—can sink. This sinking can cause problems, especially on a patio. To remedy the problem of a sunken concrete patio, refer to the steps and options below.
Step 1 – Assess the Damage
Determine the extent of the damage. If the entire patio slab has sunk, you'll need to know the following information:
A. Is one side of the slab still at the original level?
B. Has the entire slab sunk?
C. Have only certain sections sunk?
D. Have some sections separated from other sections?
E. Will broken or cracked sections need to be replaced?
Step 2 – Consider Prospective Solutions
In evaluating the damage, determine your options for repairing individual patio sections using the options below.
Option 1 – Jack the Slab
Lift the section you wish to raise by pumping cement slurry beneath it. The slurry will also fill any gaps or cavities in the base and will keep future running water from eroding the soil and causing future sinking of your slab.
Option 2 – Fill with Sand
First, separate the slab sections. This will allow you to work with those that are smaller. With a pry bar, lift and remove the section you want to be raised. Fill the area with sand and use a tamper to pack the sand until the sand is hard and level. Leave enough space between the top of the sand and the top level of concrete so that when you replace the slab it will be at the correct level.
Option 3 – Create a Partial Veneer
This process will work best with smaller slab sections. Rough the surface of the sunken slab. Drill holes into the slab surface and then pour enough mortar onto the slab surface to bring the surface up to the desired level.
Option 4 – Fill with Gravel
At expansion joints, separate the slabs and lift out those that are sunken. Stabilize the base beneath the slab you removed. You can do this by filling the hole with gravel, rocks, or bricks, then fill with sand. When the level is where you want it, replace the slab
Option 5 – Veneer the Entire Slab
If the patio slab is solid and unbroken or nor cracked, you can create a veneer of concrete to bring the surface to level. Begin by flushing the slab surface with a garden hose. The surface will need to be thoroughly clean. Build a form around the slab that will receive the new concrete fill. Be sure the top of the form is at least 2 to 3 inches high. Fill the depressions with sand and then tamp and level the sand. Fill the entire slab with new concrete, then level and finish with a trowel.