What's the Best Patio Base for Savannah's Wet, Sandy Soil?

If you live around here, you already know that the ground is different here, it does strange things. It’s sandy on top, but then it holds a lot of water after a hard rain. A patio that looked amazing one year could all of a sudden be sinking and tilting just a couple years later. Almost every time, the real problem is not the pavers, it’s the ground underneath them that you can’t see.

My name is Randy Thompson, and I started All-Out Hardscapes LLC. I actually had a career in aerospace, but I decided to build outdoor living full time instead. So, for more than 10 years now, my crew and I have put in more than 150 patios, walkways, and outdoor living areas around Savannah and the Lowcountry, from Wilmington Island to Savannah Quarters. We’re a certified Techo-Pro installer, and if there’s one thing all those projects taught me, it’s that the base is what really matters when it comes to installing a patio.

The good news is that it’s not really that complicated once somebody shows you what to look for. We’re going to tell you exactly what we build under a patio and why it lasts so long. Once you understand the layers, you can read any installer’s quote and know in about thirty seconds whether the base under your patio will last or whether it will sink.

The Best Base Here Is Stone, Not Sand

The base is the few inches of material between your dug-out yard and your pavers. It holds all the weight that lands on your patio, and it determines where rainwater runs. If you do it right, the surface will stay perfectly level for decades. But if you do it wrong, it doesn’t matter what pavers you use, it will fail and sink.

In this soil, the right base is always open-graded stone. Open-graded just means that the stone is all one size with no sand or dust mixed in, so the gaps between the rocks stay open and water runs straight through like a sieve. You don’t want to use the old sand-bed method, where the pavers are set on a layer of sand over packed gravel. That’s because sand holds water like a sponge, and around here there is so much water you can’t afford to have that issue.

That’s the whole answer. Everything we are about to tell you is just the why, so you can understand the reasoning behind what is right and wrong for a patio base. Right now, you’re not looking to put your trust in anybody, you are just making a checklist so you can tell a good base from a bad one on your own confidently.

What Is the 4-2 Base, Layer by Layer?

We call our base a 4-2, and once you hear it you will always remember it. Four inches of clean #57 stone on the bottom, two inches of clean #789 stone on top. Some people also call it a hybrid base, or a base for permeable pavers. Permeable just means water passes through it instead of running off the surface.

Here’s how we do it. We dig the area out, then put down the four inches of #57, which is a clean crushed stone about the size of a nickel. We screed it, which means we flatten it to the right height, then rake it and run a plate compactor over it. A plate compactor is a heavy machine with a vibrating steel plate that packs the stone down solid. We compact that whole layer in one pass instead of building it up bit by bit. The reason we do that is that over-compacting in layers crushes the bigger stones into smaller pieces and you lose the open structure that lets the water pass through so easily. Once the #57 is compacted correctly, you can drive a truck across it without leaving a single mark.

After that, we add the two inches of #789 on top. We flatten this layer out even more because this is the bedding layer the pavers actually rest on, so it needs to be very even. After it’s flattened out, we compact it again. Once we finish that part, the whole thing is like a concrete pad. The polymeric sand and the pavers go straight on top of it. That’s it.

Why #57 Stone Turns Your Patio Into a Giant Drain

Here’s the part most people never get told. That bottom layer of #57 is the exact same stone the county makes you pack around your septic lines and in a French drain. That’s because when they dig a septic field, they surround the pipe with #57 so that the water sinks down through the gravel, into the pipe, and gets carried off somewhere else. A French drain works the same way: water falls into the open stone and flows out, instead of sitting where you don’t want it.

Your patio is doing the same thing. With four inches of clean #57 underneath, every drop of rain that finds a joint sinks straight down into the stone and moves out through the ground and away from your patio. The whole thing essentially becomes a giant drain field, which is why our patios will never heave and float after a storm: there’s nowhere for the water to pool and push up.

This is important because of the type of ground under us. It’s mostly sand on the surface sitting over a denser, slower-draining soil. So once water works down a few inches through the sand, it hits that hard dirt layer and backs up. You can see that pattern in the USDA’s published description of the Savannah soil series.¹

On that kind of ground, drainage is the single most important thing for a good base, and a sand bed simply can’t drain the way it needs to. Sand fills the gaps that stone leaves open and holds water against the bottom of your pavers, right where it will cause the most damage.

Does the Shape of the Stone Really Matter?

It matters more than you probably think, and it’s a great question to ask any installer, because the answer will let you know if they actually know what they’re doing.

Our top layer is #789, which is a blend of number 7, number 8, and number 9 sized stone. But what’s important is that it’s chip stone, which means it has sharp, jagged edges. When you run a compactor over jagged stone, the edges bite into each other and lock together, almost like a set of teeth. It makes it set up really tight and it doesn’t move.

With rounded gravel, like the smooth stuff that sits in the bottom of a fish tank, the stone has nothing to grab. When you walk or step on it, it rolls and shifts under your weight, and you get little divots under your heels. If you build your bedding layer out of that, your pavers will telegraph every soft spot. So when someone asks why we are so particular about the specific stone we use, we explain that the shape of the rock is what holds your patio flat for a very long time.

What’s Wrong With the Sand Base Most Installers Use?

Nothing, but only if you live somewhere dry. Lots of places across the country set pavers on sand and it lasts for years. The problem here is because of our type of soil and amount of rain.

From what we’ve noticed, probably about 90% of other installers in this area still build on sand. The standard way to do it is three inches of crush-and-run, which is gravel mixed with stone dust and fine particles that pack down and become very hard. Then they top that with two to three inches of concrete sand or plain sand that the pavers rest on. It goes in fast and it looks perfect on day one.

But if you watch the water, the crush-and-run is full of fines, so it packs almost solid and slows water down instead of letting it pass through. The sand on top soaks water up and holds it against the underside of your pavers. Now every heavy Lowcountry rain adds more water into a layer that can’t drain out, it stays right under your patio. That water eventually softens the base, washes the sand around, and the pavers start to settle and tilt. In just a couple years you’re standing on a patio with low spots everywhere and lippage, which is the term for one paver sitting higher than the one beside it, so you can potentially trip on every edge. The pavers aren’t the thing that failed in this case, the base wasn’t done properly.

Does the Gravel Really Have to Be That Clean?

Yes, and unfortunately a lot of installers cut this corner. The whole reason the stone drains is that the gaps between the rocks stay open and clear of mud and dirt. The moment you let dirt, dust, or mud mix into that stone, it starts clogging those gaps, and you basically just have a sand base but with extra work.

So we stay on top of it. When we dig your yard out, we are pulling out dirt, and we work hard to keep that dirt out of our clean stone. The #57 and #789 show up clean from the supplier, and we keep them clean, even dusting off our boots and tools, until the pavers are put down. It sounds like a small thing, but it’s the difference between a base that drains for thirty years and one that silts up and quits and causes damage to your patio.

Isn’t the Polymeric Sand on Top Still Sand?

This can be a bit confusing, so let’s clear it up. After the pavers are set, we sweep polymeric sand into the joints between them. And yes, it has the word sand in the name. But it’s very different, it doesn’t behave like regular sand.

Polymeric sand is almost like grout. It is very fine, so a little of it can sift down into the top of the #57, but the moment it touches any moisture it starts to clump and bond to itself. It locks up suddenly and fills the joint, sticking to itself and to the sides of the pavers, the same way grout grabs onto subway tile. Once it cures, it stops sticking and simply holds. With a paver like the Blue 60, the whole stone actually pulls water through it, so even a little sand that works down into the gravel bonds in place the second it gets wet, it doesn’t fall down into the base layer.

It’s not permanent though. Polymeric sand is good for about three years. After that you just pressure-wash the old sand out and re-sand the joints, or top them up. It’s very routine maintenance, the system isn’t failing. The reason this method is great is that none of the patios get weeds pushing up through the joints, because there is no open dirt for a seed to take root in.

When a Full Stone Base Is More Than You Need

We’re not going to tell you every job on earth needs a 4-2. If you’re just setting a couple of stepping stones through a garden bed, or laying a small grill pad that you’ll probably redo in a few years, you don’t need to go to all that trouble. And to be fair, a careful installer setting pavers on sand can get a patio that lasts if it’s set on genuinely high, dry, fast-draining ground. The method is not the enemy. It’s just not the right move for where we live.

It also costs more up front to do it our way because there’s more stone, more digging, and more time on the compactor. But it’s better to have that conversation honestly than sell you a cheaper base that we know is going to sink in this soil. On our wet, sandy ground that sits on top of clay, the ground holds water after every storm, so an open-graded stone base is the only way we will do it. If you’d rather spend the money once than twice, that’s the version you want under your patio.

Getting Your Patio Base Right the First Time

The base is the one part of your patio you’ll never see again once it is finished, and it is the one part that decides whether you are still happy with it in ten years. Now you know what to look for. Open-graded stone instead of sand, four inches of #57 for drainage, two inches of jagged #789 to lock it flat, and clean gravel the whole way through. Take that checklist to whoever you hire, and have them walk you through their base, in inches, before anyone starts digging.