Home › Services
Concrete patios that drain on a flat Lowcountry yard
A patio is the slab most people use barefoot, sit on for hours and look at from the kitchen window, so small flaws matter more here than on a driveway. In the Lowcountry the usual complaints are puddles that linger after a storm, green or black film in shady corners, a surface too hot to cross in July, and a slab that has tipped toward the back door. Nearly all of those are decided before the concrete arrives. This page covers how to plan the size, the fall and the finish, and what clues in an estimate reveal whether those choices were considered.
Start with where the rain will go
Most yards around Charleston are close to level, and many sit only a little above the surrounding streets and ditches. A patio adds a hard surface that sheds every drop that hits it, so the first design question is simple: when a summer thunderstorm dumps a heavy rain in half an hour, where does that sheet of water end up?
The slab should fall away from the house along its whole length, gently enough that furniture does not wobble and firmly enough that water does not sit. The edge that receives the runoff needs somewhere to send it, such as a lawn that slopes onward, a gravel strip, or a shallow swale. If the yard has no low point beyond the patio, a contractor may suggest regrading, a drain, or raising the slab slightly so it is not the lowest spot on the property.
Watch for patios that end at a fence line or a raised bed. Water that reaches a barrier and has nowhere to go will soak back toward the slab and the foundation. Look at the yard during and after a hard rain before you settle on the shape.
Where the patio meets the house
The joint between a patio and the house wall is the most sensitive line on the job. The slab should sit low enough below the door threshold that wind-driven rain does not blow across it and into the house, and it should be separated from the foundation with an isolation joint so the two can move independently.
Many Lowcountry homes have raised floors, crawlspaces or slab foundations close to grade. On a raised house the patio often sits at the bottom of a set of steps, and the question becomes how the steps and the patio tie together. On a home built slab-on-grade, the patio may end up very close to the height of the interior floor, and a contractor has less room to create fall. Ask how the new surface will relate to the door, weep holes in brick, and any vents or siding near the ground.
The base under a backyard slab
Patios carry light loads compared with driveways, which tempts some installers to skip base work. Sandy Lowcountry soil can make that seem reasonable, because sand looks firm. The trouble is that loose sand shifts when water flows through it, and backyards often hold old garden beds, buried debris, stumps and soft fill left over from construction.
A sound plan strips sod and organic topsoil, removes roots and soft pockets, and places a compacted layer of crushed stone before the forms are set. The stone creates an even bed and a path for water under the slab. If a hot tub, outdoor kitchen, masonry fire feature or heavy planter will sit on the patio, tell the contractor early, because those spots may call for a thicker section or reinforcement beneath them.
Shade, humidity and the green film problem
Big oaks, magnolias and pines give Lowcountry yards welcome shade, and they also keep patios damp. In warm, humid air, a slab that rarely dries out grows algae, mildew and moss, especially on the north side of a house or under a canopy. The surface turns slick and stained.
A patio can be planned to fight that. A slightly steeper fall helps it dry. A textured broom finish grips better when damp than a smooth trowel finish. A sealer reduces how much water the surface holds, although it will need reapplying. Keeping gutters clear and trimming low branches lets more sun and air reach the slab. None of that eliminates cleaning, but it can change the chore from weekly to occasional.
Heat and color on a sunny slab
A patio in full afternoon sun gets hot. Lighter surfaces reflect more sunlight and stay cooler underfoot, while dark tints absorb it. Plain gray concrete sits in between. If the patio will border a pool or be used barefoot, color is not only a matter of looks, and it is worth asking to see samples in sunlight rather than indoors.
Heat also affects the pour itself. On a hot morning, the contractor may schedule an early start, keep materials and the base cool and damp, and cover or mist the slab once it is finished so the surface does not dry ahead of the concrete below it. A patio that cures too fast can develop a weak, dusty top layer and a web of fine cracks.
Size, shape and joints
Measure the furniture you intend to use and add room to walk around it. A table with chairs pulled out needs a lot more space than the table alone, and grills want clearance from the house siding. Curved edges look softer but add forming time; square shapes are simpler to joint.
Joint spacing usually follows the familiar ratio of two to three feet for each inch of slab depth, arranged so each panel stays nearly square. Ask to see the joint plan. It is worth lining joints up with doors, posts or the edges of a future pergola so the pattern looks intentional, and making sure a joint leaves each inside corner of an L-shaped patio, where cracks most often begin.
Checklist for comparing patio estimates
If your neighborhood has an HOA, ask whether it reviews patios, and ask the county or town whether a permit applies before anything is formed. The rules are local and not the same everywhere.
- Dimensions, thickness, and any thicker or reinforced areas for heavy features.
- Sod removal, digging out soft spots, and the stone base depth and compaction.
- Direction and amount of fall, and where runoff will be directed.
- The detail at the house: height below the threshold and the isolation joint.
- Finish type, color if any, and whether a sealer is included.
- Joint layout drawn out or described.
- Curing method and how long to stay off the slab.
Concrete patios that drain on a flat Lowcountry yard — common questions
How much should a patio slope away from the house?
It needs enough fall to move water steadily off the surface without being noticeable when you set down a table. Contractors commonly build in a gentle, even slope toward the yard. The exact amount depends on the size of the patio, the finish and how the ground beyond it drains. On a very flat lot, ask the contractor to show which edge is lowest and where the water will travel from there.
Why does my patio turn green in the shade?
Shaded concrete in humid weather stays damp long enough for algae and mildew to grow on the surface. Trees, fences and the north side of a house all slow drying. Better slope, a textured finish, a penetrating sealer and more sun or airflow all help. Periodic cleaning with a product made for concrete is still normal in the Lowcountry. Avoid harsh chemicals that can damage nearby plants or the concrete itself.
Is a broom finish or a smooth finish better for a patio?
A light broom finish leaves fine ridges that give bare feet and shoes more grip, especially when the surface is wet or shaded. A smooth steel-trowel finish looks sleek but becomes slick in rain. For outdoor use, many homeowners pick a broom or textured finish. Decorative options such as stamping or exposed aggregate are also possible, with different upkeep needs that the contractor can explain.
Can a concrete patio go over my old pavers or slab?
Pouring a thin layer over an existing surface is sometimes suggested, but it rarely works well outdoors. A thin overlay tends to crack wherever the old surface moves, and it raises the finished height toward the door. If the pavers or old slab have settled, the ground below is part of the problem. In most cases removing the old material and rebuilding the base gives a longer-lasting patio.
Will a hot tub need a special slab?
A filled hot tub is far heavier than patio furniture and concentrates that load in one footprint. Tell the contractor the model and where it will sit. They may thicken that portion of the slab, add reinforcement or plan a separate pad with its own base. Also ask the maker for their support requirements and check with the county or town about any electrical or permit questions before the pour.
How soon can furniture go on a new patio?
People can usually walk on a new slab after a few days, but heavier items such as grills, planters and loaded tables are better kept off until the contractor says the concrete has gained enough strength. Dragging metal furniture can scratch a fresh surface, so lift pieces into place. If a sealer is going on later, ask whether furniture needs to come off again for that step.
Talk through your project
Start with the address, what you want poured or replaced, rough dimensions, and a few photos of the area and any existing concrete.
Related work
Concrete Driveways
New drives, widenings and tear-outs built on sandy, low-lying ground.
Stamped & Decorative Concrete
Pattern, color and exposed aggregate, with sealers chosen for sun and humidity.
Walkways & Steps
Front walks and steps up to raised entries, planned around tree roots.
Garage, Shed & RV Slabs
Garage, shed, boat and RV pads sized for the weight and the water table.
Concrete Repair & Replacement
Reading cracks and sinking to decide between lifting, patching and replacing.