Why Do Paver Patios in Savannah Start Sinking After 3 Years?

If you’ve noticed a corner of your patio dropping, or a few pavers tilting and rainwater pooling when it used to run off, you’re seeing the beginning of something that happens to a lot of patios in this area, and it usually shows up after three years. You aren’t imagining it, and you didn’t do anything wrong by walking on it.

My name is Randy Thompson, and I’m the founder of All-Out Hardscapes LLC. We build paver patios and outdoor living spaces all across Savannah and the Coastal Lowcountry, from Wilmington Island to the gated streets of Savannah Quarters. In the last ten or more years we’ve put in more than 150 patios. We’ve also pulled up lots of other people’s patios to find out why they failed. The reason is almost always the same and it hardly ever has anything to do with the pavers themselves.

Here’s the part most homeowners are never told: a paver patio doesn’t sink because the pavers are bad, it sinks because of what’s underneath it. Once you understand what’s going on just a few inches below, the three-year failure that often happens isn’t a mystery anymore, and neither is the solution.

It’s Almost Never the Pavers. It’s the Base.

When a patio starts to sink, the pavers are usually blamed. Because they’re the part you can see, they take the heat. But a quality concrete paver is a dense, manufactured block that is built to carry weight and deal with our climate for many years. It isn’t usually the thing that fails.

The work that nobody sees is what fails. A patio is only going to be as flat as the layers underneath it: the base, made of compacted stone that carries the load, and the bedding, a thin layer that the pavers sit directly on. If those two are done right then the surface will stay put. But if those are done incorrectly then gravity does the rest, usually in three to five years.

The most common method in this area builds those layers to trap water rather than move it, and that one decision is what puts a patio on the clock.

What’s Actually Happening Under a Sinking Patio?

Here is how most patios in this area are designed. The crew puts down about three inches of crush-and-run, which is a gravel mix of crushed stone and stone dust that will pack down hard and tight. Then they will put down two or three inches of concrete sand or plain sand on the top as the bedding layer, and set the pavers on top of that. This looks solid on the first day, but the problem is what happens the first few times it rains hard.

When the first real rain happens, the sand in the joints between the pavers begins to wash away, and once that joint sand is gone, water will seep down through the open joints into the bedding layer below. This is where the packed gravel causes a problem. Crush-and-run is meant to be tight, so water can’t drain down through it. So the water has nowhere to go, and it will just sit in that sand and run down the slope of the patio, taking the sand along with it as it goes.

If you’ve ever dumped a bucket of water out on the beach, you’ve seen this happen. The water cuts a small channel through the sand and goes downhill. That same thing is going on under thousands of patios right now, just a few inches below the surface. The bedding sand washes out into channels, and that causes gaps to open up under the pavers. In three to five years after that, the pavers drop and tilt into the gaps. The sand that was holding them level is just gone.

So when someone tells us their patio is sinking, we already know what we’re going to find when we lift a few pavers: washed-out sand and empty gaps where solid support used to be.

Why Does Savannah’s Soil Make This Worse?

Our ground doesn’t do you any favors here. Most of the Savannah area is on what soil scientists call the Savannah series: a sandy loam on top with a denser, clay-heavy layer below it that swells when it gets wet and shrinks back as it dries. This is described in the USDA soil survey for the series.¹

You might want to read that again because it matters. The top is sandy, and that means water goes through it and carries loose bedding sand along with it. The layer below is tight, so once water gets down there it is likely to sit instead of soaking away. You have a surface that lets water in and a subsoil that holds it. For a patio that is built on sand, that’s close to a worst case: the washout starts faster, and the trapped water has longer to do its damage.

Then you have the rain we get on the coast added to that, season after season, and the three-year issue doesn’t seem like bad luck anymore. It’s the soil and the climate together doing exactly what they always do to a base that wasn’t built to drain.

How a Patio Should Be Built So It Drains Instead of Sinks

The solution isn’t a better paver or a thicker slab of concrete. It’s the base that gets water away from the underside of your patio instead of holding it there, and that is the whole solution.

On all our patios we use what we call a four-two base. It is four inches of clean number 57 stone for the base, and two inches of clean number 789 stone for the bedding layer that the pavers sit on. Clean is the important word. This is open-graded stone, and that means it’s been washed so there is no fine dust that packs tight, so water will go straight through the gaps between the stones instead of getting trapped. There isn’t any sand bedding layer at all, so there isn’t any loose sand to wash out from under your pavers in the first place.

This is the part we always explain to homeowners, because it makes the whole thing make sense. Number 57 stone is the exact same rock that the septic workers put around the pipes in a leach field, and it is also what goes into a French drain. The reason is simply because it drains. Water sinks down through that clean gravel and moves along somewhere else instead of making a pool in one place. When we build your base out of it, we’re turning your entire patio into a giant drain field. The rain that used to wash a sand base out from underneath the pavers can now pass right through the stone and just keep moving. The pavers stay sitting on a surface that does not crumble away.

That’s the difference between a patio that is completely flat after ten years and one that is starting to erode from the first rainy season. Same pavers on top, but a completely different story underneath.

What Are the Early Signs Your Patio Is Settling?

If you already have a patio and you are wondering if yours is going to be in trouble, you don’t have to wait until a corner collapses to find out. The early signs are barely noticeable, and they tend to show up in just about the same order. Here is what to watch for:

• Standing water: Water that pools in spots after it rains instead of running off the way it used to. Standing water where there wasn’t any is usually the first sign.
• Washed-out joints: Joints between pavers that look low, empty, or washed out, especially after a heavy storm. When joint sand is missing, that is the leak that begins the whole process.
• Tilting or rocking pavers: Individual pavers that have started to tilt, rock under your foot, or are a little bit lower than the ones around them. The difference in height between two pavers is called lippage. It means the support underneath has gone uneven.
• A dip in the field: A dip or low spot forming out in the field of the patio, often near a downspout, a low corner, or wherever water normally drains across the surface.
• Spreading edges: Edges or borders that have started to shift outward, which allows the field of pavers to spread and drop.

One or two of these on a new patio means that you should keep your eye on it. Several of them together usually means the base is washing out underneath, and that will probably get worse, not better, with each rainy season.

When Some Settling Isn’t a Crisis

We will be honest with you. Not every sunken paver is a disaster, and we’d rather you know the difference instead of panicking over just a small dip.

A brand new patio will settle a small amount as everything moves into its final place, and that’s normal. A single paver that’s dropped near a downspout could just need to be reset and the joint filled again, not a whole new patio. And sometimes the cause really is simple, like a tree root, a critter that tunneled through, or a place where a garden hose ran for years. Those are local problems with local fixes.

What we’re talking about in this article is different. It’s the slow, spreading kind of failure that comes from underneath, with a base that’s trapping water instead of letting it drain. When that is the cause, patching the surface doesn’t fix anything, because the real problem is underneath. An honest installer will tell you which one you are dealing with and if your patio can be saved or really does need to be rebuilt on the correct base. We are builders, not a patch-and-pray operation, and our whole goal is to build yours once so we don’t have to come back later and fix it.