Concrete Slab Sinking on One Side?
What Texas Clay Soil Is Doing

A concrete slab that sinks on just one side is almost always a soil moisture imbalance under that edge. Texas clay swells when it is wet and shrinks when it is dry, and a slab edge that sits over drier soil pulls away from the slab and drops. The fix is never the same for every yard, because the thing drying out that one side is never the same for every yard.

Here is the honest version from a crew that pours and repairs concrete in Seguin for a living. Most one-sided sinking you can catch early and slow down yourself. A smaller share of it is past that and needs real repair. Knowing which one you are looking at saves you from paying for the wrong fix — or from ignoring one that is about to get expensive.

Why Texas Clay Soil Does This

The ground under most of Guadalupe County is expansive clay. That means the soil acts like a sponge. When it is wet, it soaks up water and swells, pushing up against whatever sits on top of it. When it is dry, it gives that water back and shrinks, pulling away and leaving empty space.

A concrete slab is heavy, but it is not heavy enough to keep clay from moving under it. When the clay under one edge dries out and shrinks, that edge loses its support and settles. The middle of the slab, or the other side, may still sit on stable wet clay and stay put. That is how you get a slab that drops on one side and stays level on the other. The slab is not broken — the ground under part of it went away.

This is the same clay behavior that pulls soil away from your slab edge in a drought. If you have seen those gaps, the sinking slab is the next step in the same story — see our write-up on soil pulling away from a slab in Texas heat.

The Classic Trigger Patterns

One-sided sinking almost always has a cause on that side of the house. If the whole slab were settling evenly, you would look at the slab. When one side drops, you look at the yard around that side. Four things do this over and over in Central Texas:

• A downspout dumping at one corner. Rain comes off the roof and pours straight into one spot. It either keeps that corner soaked and swelling while the rest dries, or it washes soil out from under the edge. Either way, that corner drops.
• A big tree drinking from one side. A mature tree on one side of the slab pulls water out of the clay through its roots all summer. That side dries and shrinks; the far side, with no tree, stays wetter and holds up.
• A drainage path along one edge. Water runs across the yard and down one side of the slab every rain, carrying fines away and drying that edge out between storms. Over a few seasons that edge settles.
• Drought years. In a long dry stretch, the side of the slab that gets the least water — shaded, paved uphill, or just farther from any irrigation — shrinks the fastest. The slab follows.

Notice that none of those are about the concrete. They are about what the concrete is sitting on. That is the whole secret to one-sided sinking.

The Honest Decision Framework

Not every sinking slab needs a contractor this week. Some need drainage work and a watchful eye. Some need to be lifted. A few need to come out. Here is how Big T sorts them without selling you something you do not need.

Hairline settlement cracks with no trip hazard — fix drainage and monitor. If the cracks are fine, the slab edge has not lifted into a lip, and your doors still work, the slab is telling you it has started to move but has not gone far. Fix the water first. Extend the downspout, redirect the drainage path, and keep the perimeter moisture even. Then watch it for a season. A lot of these never get worse.

A sinking edge with a lip or a trip hazard, or doors that stick — time to talk lifting. When one side has dropped enough to make a lip, trip a foot, or drag a door, watering will not raise the concrete back. Now you are in the repair conversation. There are real options here — mudjacking and polyurethane foam are the two main ones — and the right one depends on your slab, your soil, and what the slab carries. We are not going to quote you a price we do not know over the phone, because the honest answer changes with the job.

Badly cracked or broken through — that section may need to come out. If the sinking edge is shattered into pieces, or the subgrade has washed out so far that lifting would just drop again, a repair that lifts the old slab is throwing good money at a bad base. Sometimes the right call is cutting out that section, fixing the base, and re-pouring. That is a bigger conversation, but it is the one that lasts.

The line between these is not something you can read off a spec sheet. It is something you see standing on the slab. Which is exactly why we come look before we quote anything.

Check It Yourself First

Before you call anybody, do three things yourself. They take ten minutes and they tell you, and us, a lot.

Measure the lip height. Where the sinking slab meets the next section — a walk, a drive, another pour — lay a straight board across the joint and measure the drop. A quarter inch is a watch item. An inch or more is a repair item. Write it down and date it, so you know next month whether it moved.

Look at where the water goes after a rain. Wait for the next good rain, then walk the slab edge while it is still wet. Where does the water pool, where does it run off, and does it dump at one corner? That water path is usually the same path that is drying out — or washing out — the soil under the sinking edge.

Check the doors on that side of the house. Open and close every door on the sinking side of the building. If one sticks, drags the floor, or will not latch, the slab under it has moved enough to twist the frame. Sticky doors are one of the earliest signs a slab edge is dropping, and they show up before the lip is big enough to trip over.

Do those three and you already know more than most folks do when they call. If the lip is small and the doors work, you are in the monitor-and-fix-drainage group. If the lip is real or the doors are sticking, you are in the come-look group.

Big T's Straight Talk

Here is the part some contractors will not tell you. A sinking slab edge is not always an emergency, and it is not always a repair. I have walked away from jobs telling folks to fix a downspout and come back in a year, because that was the honest call. I have also told folks the slab was past saving and the cheap thing to do was the thing that would actually hold up.

The ones I worry about are the ones who call after it is already a trip hazard and two doors are sticking. That is when a $400 drainage fix has become a real repair. So do the three checks above. If you are in the watch group, fix the water and keep an eye on it. If you are in the repair group, call us and we will come look at it, tell you straight, and give you the real options — mudjacking, foam, or a re-pour — without inventing a price over the phone.

We pour concrete in Seguin every week. We know what this clay does because we work on top of it. If your slab is sinking on one side and you want an honest read before you spend a dime, that is what we do.