What is under and around a slab decides how long it lasts. Nashville has clay that swells and shrinks, limestone close to the surface, steep lots and heavy rain. Here is how each one affects a concrete job.
Do I need to worry about drainage?
Yes. Drainage is the first thing to plan here. Clay soaks up water slowly, and rock under it stops water going down at all, so rain runs across the surface. Every slab should slope so water leaves it, about an eighth to a quarter inch per foot, and the water needs somewhere to go: the street, a swale or a drain. A slab that traps water against a house or lets it run along its own edge will be undermined.
My patio or driveway slopes toward the house. Can that be fixed?
Yes. A slab that slopes toward the house or garage can be fixed in three ways. A sunk slab can be lifted back to its proper slope. A channel drain can be cut in across the low edge and piped to daylight. Or the slab is replaced with the fall reversed. On a drive that runs downhill to a basement garage, common on hilly lots here, a trench drain in front of the door is the standard cure.
Can tree roots crack or lift concrete? Can I fix the concrete and keep the tree?
Tree roots can lift and crack concrete, and the big oaks, maples and hackberries on older Nashville streets do it often. Often you can keep the tree. Options include grinding the raised lip, pouring the new section thinner over a gravel bridge, curving the walk away from the trunk, or using pavers near the tree. Cutting large roots close to the trunk can make a tree unstable or kill it, so have an arborist look before any big root is cut. Metro also has tree rules for some sites and for street trees.
My neighbor's concrete sends runoff onto my property. What can I do?
Start by talking to the neighbor and showing them where the runoff goes in a storm. Often a downspout extension or a small curb solves it. If new paving next door redirected water onto your lot, you can report it to Metro Water Services Stormwater through hubNashville, since Metro regulates added impervious area. A property owner who changes the natural flow and causes damage may be liable under Tennessee law. That is a question for a lawyer, and this is general information only.
Does clay or soft soil change the job?
It does. On clay we dig out the topsoil and soft spots, put down compacted crushed stone and use steel in the slab, because the ground will move a little every year. We also keep water from collecting at the slab edge, since wet clay swells and dry clay shrinks. On fill dirt beside a new house, the base has to be compacted in layers or the slab will settle.
What if there is limestone rock or a sinkhole under my yard?
Shallow limestone is common in the Nashville basin. For a flat slab it is good support. It becomes a cost when a footing, a wall or a drain trench has to go through it, because it must be broken out with a hammer. Sinkholes are less common but real in this area. A round dip that grows, or a slab that drops suddenly with a hole beneath, should be looked at by a geotechnical engineer before any concrete is poured over it.
My gravel driveway turns to mud. Is concrete the answer?
A gravel driveway turns to mud when the stone has sunk into the clay and water has no way out. Concrete solves it for good, but only on a proper base. The mud and soft soil come out first, fabric and fresh compacted stone go in, and then the slab is poured. Pouring straight over the muddy gravel gives a slab that cracks. On a long drive, concrete on the steep or wet parts and gravel elsewhere is a fair way to save money.
My patio was poured over an old utility trench and settled. Why?
Because the trench was never compacted. When a water, sewer or gas line is laid, the soil put back in the trench is loose and keeps settling for years. A slab across it sags or cracks along the line of the trench. The repair is to lift the slab if it is whole, or cut out the strip over the trench, compact stone in its place and repour with steel tying the new piece to the old.
Should I raise a patio or slab in a flood-prone area?
Get advice from Metro before you add fill. In a mapped floodplain, raising ground or adding fill is restricted, because it pushes flood water onto other lots. The May 2010 flood showed how far the Cumberland, the Harpeth and Mill Creek can reach. Metro Water Services handles floodplain questions for Davidson County. Outside the floodplain, in a yard that just ponds, a slightly raised slab with the edges graded away works well.
The only real price is one written after we have measured your site. Call (615) 436-8921 or text us a photo of the area for a free on-site estimate.