Almost every cracked patio we get called out to in Dallas-Fort Worth cracked for the same reason, and it is not bad concrete. It is the ground underneath, which in most of this metroplex moves more in a single year than the slab can tolerate.
The ground here is the whole story
Drive east from Fort Worth and the dirt changes twice. West of the Trinity you are on Fort Worth Prairie — thin soil over limestone, where the problem is rock, not movement. Through Denton, Argyle and Aledo you cross the Eastern Cross Timbers, a sandy loam sitting on clay. And from roughly I-35 east across Dallas, Plano, Frisco, McKinney, Rockwall and Forney, you are on Blackland Prairie — deep, dark, smectite-rich clay.
That last one is the reason for most of the cracked flatwork in this metroplex. Blackland clay is expansive: the mineral structure takes on water and physically grows. A wet April swells it. By late August, after eight weeks of heat with no rain, it has given that water back and shrunk — which is why you see the gaps open up around your foundation every summer, wide enough to lose a tape measure in.
The vertical movement that produces is not subtle. Across one wet-to-dry cycle, untreated Blackland clay commonly moves on the order of two to four inches, and more where a large tree is pulling moisture out of one side of the yard. Now picture a rigid concrete slab sitting on top of ground doing that unevenly. Something has to give, and concrete is strong in compression and weak in tension. It gives by cracking.
How to read the crack you already have
Not every crack is a problem. Before you get quotes to tear anything out, it is worth spending five minutes working out which kind you have.
| What you see | What it usually means | Worth acting on? |
|---|---|---|
| A straight, clean line across the slab, often in a grid | A control joint — a deliberate weak line, either tooled in or saw-cut, so the inevitable shrinkage crack happens where you chose | No. This is the system working |
| Fine hairlines, under about 1/16 in, no height difference | Normal curing shrinkage in the first year | No, but seal them to keep water out |
| A crack running diagonally off an inside corner | Stress concentrating at the corner — often a slab poured around a post or a step-down without a re-entrant joint | Yes, monitor it |
| One side of the crack sits higher than the other | Differential movement. The subgrade under one half is doing something the other half is not | Yes. This is the one that matters |
| A crack that opens in summer and closes in spring | Classic expansive-clay cycling | Yes — fix the water before the concrete |
| Cracking plus water pooling within 3 ft of the house | Drainage is feeding the movement, and it is heading for your foundation next | Yes, urgently |
The quick test for the one that matters: run a straightedge or a level across the crack. If the two sides are flush and stay flush through a season, you have a cosmetic crack. If there is a lip you can feel with a fingertip, the subgrade is moving differentially, and resurfacing over the top of it will simply crack again in the same place within two summers.
Why slabs fail here, in plain terms
When we are called to look at a failed patio in Plano or Rowlett or Mansfield, it is nearly always one of five things, and usually two or three of them together.
- No joint plan. Concrete shrinks about 1/8 in for every 20 ft as it cures. That movement is going to relieve itself somewhere. Control joints are how you decide where — cut deep enough (a quarter of the slab thickness) and spaced at roughly 24 to 30 times the thickness, so a 4 in slab wants joints every 8 to 10 ft.
- Water sent the wrong way. A slab that slopes back toward the house, or downspouts dumping at the patio edge, keeps the clay under one edge permanently wet while the rest dries out. That is a movement machine.
- Subgrade never prepared. Pouring straight onto scraped clay with no moisture conditioning and no compaction means the slab inherits every bit of that clay’s behavior.
- No steel, or steel lying on the dirt. Rebar or mesh does not stop cracks; it holds the two sides together and flat after one forms. Sitting on the subgrade instead of up in the slab, it does nothing at all.
- Poured against the house with no separation. Tie a patio rigidly to a foundation that moves on its own schedule and one of them will lose.
What actually works on this ground
There is no product that makes expansive clay stop moving. Everything that works is about either keeping the moisture content under the slab stable, or building a slab that can ride the movement without tearing.
Solve the water first
This is the unglamorous half, and it is the half that decides whether the rest was worth paying for. Positive fall away from the house at a minimum of a quarter inch per foot. Downspouts extended and discharged well clear of the slab, not at its edge. Where a yard traps water — and plenty of flat North Texas lots do — a French drain or a channel drain to daylight. On a bad lot this can cost more than the concrete. It is still the right order to spend the money in.
Then build the slab for movement
- Thickened edges. A perimeter beam turned down 12 to 18 in stiffens the slab where the soil dries out first.
- Real steel, properly positioned. #3 bar on 18 in centers, chaired up into the middle third of the slab.
- Joints on a drawing. Placed before the pour, cut within 6 to 12 hours of finishing, aligned with columns, corners and any change in slab width.
- An expansion joint against the house. The patio and the foundation get to move independently.
- Moisture-conditioned, compacted subgrade. Clay brought to the right moisture and rolled, so it starts life near the middle of its range rather than at one extreme.
For larger slabs, or anywhere the soil report comes back with a high plasticity index, post-tension is worth pricing. Cables tensioned after the pour keep the whole slab in compression, so it behaves as one stiff plate instead of a set of panels. It is the same logic used under most new houses on this ground, and it is the reason those foundations outlast the flatwork beside them.
Repair or replace?
Honest answer: it depends almost entirely on whether the two sides are flush.
Flush, stable, cosmetic. Clean and seal the crack, then a proper overlay or coating will give you a surface that looks new and lasts, as long as the joints below are honored in the new surface. This is the cheapest good outcome and it is real — a well-prepped decorative coating over sound concrete is a genuinely durable finish, not a cover-up.
Lipped, or moving through the seasons. Resurfacing is money you will spend twice. The crack telegraphs through, usually within two summers, because nothing about the cause changed. Here the honest options are to tear out and repour with the drainage fixed and the slab detailed properly, or to do something else with the space entirely — a raised deck, or segmental paving, which is jointed every few inches by design and can be lifted and reset instead of demolished.
When to pour
Fall and winter beat summer here, for two reasons that both work in your favor. Soil moisture is more stable between October and March, so the slab is not being placed on ground at one extreme of its range. And concrete placed in cooler weather cures more slowly, which produces a denser, stronger result — the opposite of a July pour flashing off in a hot wind before it has finished hydrating.
If you are planning a patio for next spring, the design and permit work is worth starting now. Most DFW cities take two to six weeks on a permit for covered structures, and the good crews book out further in spring than they do in November.
The bottom line
A patio in North Texas is not really a concrete job. It is a drainage and soil job with a concrete finish on top. Contractors who price it as the second thing are cheaper on the day and more expensive over five years.
If you have a crack you are not sure about, take a photo with a straightedge laid across it and send it over. We will tell you which of the six rows in that table you are looking at, and whether it is something to act on — that answer is free, and it is often “leave it alone”.
Questions we get asked about this
Not usually, but it is a signal worth reading. A patio slab is thinner, unreinforced by comparison and unprotected from moisture swings, so it shows soil movement long before a post-tension house slab does. If the patio is cracking and water also pools near the house, deal with the drainage now — that is the shared cause.
Four inches is the common residential standard, and five inches with thickened edges is a meaningfully better bet on Blackland clay. But thickness is the least important variable here. A 5 in slab on unprepared clay with no joint plan will crack, while a well-detailed 4 in slab on conditioned subgrade with drainage solved will not.
If the crack is flush and stable, yes — a properly prepped overlay or coating is durable and looks new. If one side sits higher than the other, resurfacing will fail in the same place within a couple of summers, because the movement causing it has not changed.
Flatwork at grade typically does not, though many cities cap impervious cover across the lot. Anything with a roof, a footing or electrical almost always does. Rules differ city to city, so it is worth confirming before design rather than after — we handle the submittal on projects we build.
October through March. Soil moisture is more stable, so the slab is not placed on ground at one seasonal extreme, and cooler temperatures let the concrete cure slowly, which makes it stronger and less prone to shrinkage cracking than a mid-summer pour.
