Around New Orleans, concrete is only as good as the ground and the water

A delta city built on ground that is still moving

The land under the south shore was built by the Mississippi River, one flood at a time, out of silt, sand and clay. The coarsest material settled right beside the channel and formed the natural levees, the slightly higher ridges where the oldest parts of the city stand. Finer clays settled farther back, in the low basins that became cypress swamp and marsh between the river and Lake Pontchartrain. Those basins were drained to build much of the modern metro.

Drained swamp soil does not stay put. As water leaves soft clay and buried organic layers, they shrink and compress, and the surface slowly sinks. That gradual settling is one of the best-known facts about the region, and it is the single biggest reason concrete here tilts, cracks and pulls away from houses. The ground under a slab may be settling a little every year, and it rarely settles evenly.

What a slab can tolerate depends on how that movement reaches it. Concrete handles weight pressing down on it very well, but it has little ability to bend. When one corner loses support, or a strip along one edge sinks faster than the middle, every car or footstep over that spot flexes the slab until it cracks along the line where support changes. The goal of good preparation is not to stop settling, which is impossible, but to make it slow and even.

Houses that hold their height and yards that do not

Many homes in the area are supported on something firmer than the surface soil. Older houses in the city often stand on brick piers a few feet above the yard, and a great many newer homes rest on driven pilings. The building holds its height while the driveway, the walk and the patio, resting directly on the ground, drift slowly down around it.

The result shows up in predictable places. A lip grows at the garage threshold. A front stoop separates from the porch and leans outward. A gap opens under the edge of a patio next to the house, and rain running into that gap washes out more of the base. A new pour placed the same way as the old one will usually repeat the problem, so ask any contractor how the new concrete will meet the house and how that joint will behave as the soil keeps moving.

Rain, heat and storms: the climate a slab has to live in

New Orleans gets a great deal of rain, much of it in short, intense summer storms that can briefly overwhelm street drainage. On a flat lot, a slab with too little fall or a lawn built up higher than the concrete leaves water standing for hours. Standing water softens the soil at the edges, feeds algae and mildew on the surface and, over time, carries fine material out of the base.

Heat and humidity matter on the day of the pour. A hot, breezy afternoon can pull moisture from the surface of fresh concrete faster than the slab below it cures, which leaves a weaker skin that dusts or flakes. Humidity also affects decorative sealers, which can turn cloudy when trapped moisture is sealed in. Contractors here commonly start early in the day and take care with curing and sealing.

Hard freezes are uncommon, and road salt is rarely part of the picture, so the freeze-thaw damage that dominates concrete advice in colder regions matters much less here. Hurricanes and tropical storms are the bigger seasonal concern. Long stretches of saturated ground after a storm reduce support under slabs, and it is common to notice new cracks or dropped edges once the water recedes.

The steps that decide whether a new slab lasts

Put two freshly finished slabs side by side and they may look identical, yet a few hurricane seasons later one is flat and the other is broken. Most of the difference comes from work that is buried or finished before anyone judges the surface, so it is worth asking about before the job begins.

Excavation and base

Grass, roots and dark organic topsoil should be removed, along with any spongy material found beneath them. A granular base, commonly crushed stone, is then placed and compacted in layers. On soft clay a firm, compacted base spreads the load and gives trapped water a way out. It is fair to ask the digging depth up front, along with the plan for any soft pocket uncovered.

Thickness and reinforcement

Driveways, walks and patios are commonly about four inches thick, with thicker sections where a boat trailer, camper or work truck will sit. Wire mesh, rebar and fibers help hold cracked concrete together and level, and steel only works when it is supported inside the slab rather than lying on the stone.

Joints

Control joints give shrinkage cracks a straight place to form. On an ordinary four-inch slab they typically land somewhere around eight to twelve feet apart, and they need to be cut promptly. Isolation joints separate the slab from the house, steps and other slabs so each part can move on its own.

Fall and drainage

Each surface needs enough pitch to push rain away from the walls and onward to somewhere it can actually drain. On level lots that often means looking beyond the concrete to the lawn, the downspouts and the street.

Request an estimate visit

Send the property address and a line about the project: a new pour, a replacement, or concrete that has started to sink, crack or hold water. A reply will follow to arrange a visit.

The main types of home concrete projects

Home concrete sorts into a handful of job types, and plenty of projects mix two or three. Replacing a drive frequently means redoing the front walk as well; a new patio may call for steps down from a raised back porch. Pattern stamping, integral color and exposed stone are finishes that suit most of these, and each one carries its own upkeep. Repair sits apart, because the first question is whether the slab can be saved at all.

Details worth gathering before the estimate visit

Treat this as a short checklist, not homework. Even approximate answers help the first call skip straight to what matters.

• The address, and whether the neighborhood has an HOA or sits in a historic district.
• What you want built or repaired, with rough dimensions paced off on the ground.
• What will rest on it: cars, a pickup, a boat on a trailer, a camper, a hot tub or furniture.
• Whether old concrete, pavers, asphalt or shell has to come out first.
• Whether the house sits on piers, pilings or a slab, if you know.
• Where water collects after a heavy storm and where the downspouts empty.
• How a concrete truck or pump could reach the spot through gates, alleys or narrow side yards.

If the project touches the street, a sidewalk, a ditch or a flood zone, ask your parish or city office what approval applies, and check with your HOA or review board too. The requirements are theirs to state and differ across the region.

From first message to finished slab

After you reach out, the next step is an on-site look. Standing in the yard, the contractor can judge the soil, the grade, the route runoff takes off the lot, the reason an old slab gave out and the way equipment will get in. A job that sounds like a simple replacement may turn out to need drainage changes or a deeper base once someone stands on it.

Then the estimate arrives in writing. The helpful kind names the square footage, thickness, digging and base work, steel, joint plan, surface finish, tear-out and the drainage plan. Line those items up side by side when you compare offers, because two totals for one yard frequently price two very different pieces of work.

Once you say yes, the calendar bends to the weather. July pours often begin at sunrise, and a tropical system in the Gulf can push a date back. When the slab is down, the contractor will tell you when it is ready for feet and, later, for tires.

Where homeowners send requests from

Requests come mainly from three parishes: Orleans on the south shore, Jefferson wrapped around it on both banks of the river, and St. Tammany across the lake. Soil, lot size and drainage change a lot between them and even between neighboring blocks, so the visit counts for more than the ZIP code.

New Orleans concrete questions, answered plainly