How Do I Repair Sinking Flagstone?

Answered by Brett ~ November 14, 2011 ~ Comments

The front stoop of my home is covered in flagstone, presumably laid over concrete. The flagstone has sunk and now drains towards the house. What is the best way to fix this issue?

Mike S. ~ Greenville, SC

Brett Kulina

Mike, if the concrete patio in front of your home has settled and is causing water to drain towards your house, then you may eventually have unwanted water pooling in your home's crawlspace or basement. It is imperative that a home has positive drainage around its perimeter, which moves surface water away from the structure. In general, you can expect adequate drainage when the finished grade is sloping away from a home's foundation, falling at least a few inches within the first 6 feet.

My guess is that your concrete and flagstone patio has slumped because of underlying voids caused by improperly compacted fill material. Without ripping up the existing patio and installing additional fill, the best way to solve your problem is going to be to hire a concrete contractor to do some mud jacking for you. Mud jacking is when pressurized concrete grout is injected underneath an existing slab in order to raise the level of the slab's finished surface. This process takes specialized tools and training and is well beyond the abilities of most DIY'ers.

When trying to lift a concrete slab, a concrete contractor will core drill several holes in a the slab and then inject pressurized grout through the holes in order to fill the voids beneath the slab. If the slab lacks enough structural rebar, or the contractor injects too much pressurized grout, then there is a chance of cracking the slab, which could mean you would have to replace the slab regardless. Your best bet is to have a concrete contractor who works in the Greenville area inspect your home's patio and offer you some potential solutions and cost estimates.

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