Gravel Base vs. Sand Base for Pavers: Which Lasts in Savannah's Wet Soil?

If you’re comparing patio bids in Savannah, you’ve noticed there’s a big price gap and you keep getting different opinions about what goes under the pavers. One crew swears that sand is the best, but another will tell you that gravel is the best. On the day the work gets finished, both patios look exactly the same. You’re not going to see the difference until three to five years later, after a lot of rain, when one patio is still flat and the other is riding up at the corners and has tilting pavers.

My name is Randy Thompson, and I actually left a career in aerospace so I could start my business, All-Out Hardscapes LLC. Over the last 10-plus years, our crews have built more than 150 patios, walkways, and outdoor living spaces across Savannah and the Coastal Lowcountry, from Wilmington Island to Savannah Quarters. The base is the part homeowners ask us about the least, and it’s the most important part of the whole thing. What you need to know is that in our particular type of soil, the base has to drain, or the patio will move, period.

We’re going to give you the real comparison, gravel base versus sand base. This information is written for our soil and our specific amount of rain and not for some dry climate where sand or gravel both work fine. By the end of reading this article, you’ll know which one we would put under our own homes, and exactly why.

So Which Base Actually Lasts in Wet Soil?

The open-graded gravel base lasts. In our ground, the real question isn’t just gravel versus sand. It’s whether the layer under your pavers lets water move or whether it just holds water in place. A gravel base drains the water away, but a sand base holds water, and water is what wrecks a patio.

That’s because our coastal-plain soil is sandy on the surface with a denser, slowly draining layer underneath, so rainwater doesn’t soak straight down and vanish like it does in a lot of places. It hangs out right near the surface, which is exactly how the USDA Official Soil Series Description characterizes the sandy, slowly permeable soils of this coastal plain.¹ When the bedding layer under your pavers is sand, that trapped water actually washes away the sand after a while. When the bedding is clean, open-graded stone, which is crushed rock with the fine dust all screened out so there are open gaps between the rocks, the water runs through the gaps and keeps going, the stones don’t move. Same amount of rain, but the results are totally different.

What’s the Difference Between a Sand Base and a Gravel Base?

Both methods start the same way, by digging out the area and compacting the dirt underneath. From there they are both done differently. Here’s how each different method is done.

A Sand Base (How Most Patios Around Here Are Built)

A sand base is the most common method. We would say that nine out of ten patios in this area are built with sand underneath. The crew lays down about three inches of crush-and-run, which is a gravel mix that still has the stone dust and fine particles in it, so it packs down really tight and dense. They compact that, then come back with two to three inches of concrete sand or basic sand as the bedding layer. They screed it so it’s smooth, and then set the pavers directly on the sand.

Installation is very fast, and it costs less, because sand is cheap and the method is quick. On day one it looks exactly the same as every other patio you see. The problem is that the dense crush-and-run with the sand on top doesn’t play well with water, which is what we are about to explain.

An Open-Graded Gravel Base (How We Build)

An open-graded gravel base installation doesn’t use sand at all. We use four inches of clean number 57 stone, which is crushed stone about the size of a quarter with the fine dust washed out so water just flows right through it. That 57 goes on the bottom. On top of that goes two inches of clean number 789 chip stone, a smaller, jagged crushed stone, as the bedding layer the pavers sit on. There’s no sand layer anywhere in the build. We just call it a four-two base, but some people call it a hybrid base, or a base for permeable pavers, which are pavers that let water drain between them.

It costs more up front, because clean stone costs more than sand and the work is a bit more involved. But that extra cost gives you a base that drains instead of one that traps water. Everything about how long your patio stays flat comes back to that.

Why Does Sand Wash Out From Under Pavers Here?

This is the part you’ll really never see, because it happens underground. The joints between your pavers are filled with sand too. After the first hard rain, that joint sand starts washing out of the gaps. Once there are gaps between the pavers, water runs straight through them into the sand layer underneath.

Here’s where it goes wrong. If you’ve ever poured a bucket of water out on the beach, you’ve seen how it cuts a little channel through the sand on its way down. That same thing happens under a sand-set patio. The water hits the bedding sand, and because the dense rock under it won’t let the water sink and drain away, the water has nowhere to go but sideways. It follows the slope of the patio and carves channels through the sand, washing the sand out with it. Once there is no sand under a paver, it has nothing holding it level anymore. That’s why, three to five years in, you see pavers coming up at angles and pointing in different directions. The pavers aren’t the issue, it’s what’s under them.

And our particular soil conditions make that problem worse. We get heavy rain and hard summer downpours, and like we said, our ground holds that water right up by the surface instead of letting it drain. You can’t use a method here that is dependent on water staying out of the bedding layer of your patio, we simply get too much rain for that to be effective.

Why Does a Clean-Stone Base Drain Instead of Trapping Water?

Think about why the crew that dug out your septic system packed number 57 stone around the pipe and the leach field. That’s for drainage. Water sinks down through the open gaps in the stone, into the pipe, and gets carried off somewhere else. The same stone is what goes in a French drain, which is a gravel-filled trench built to collect water and move it away, for the same reason. That’s exactly what a number 57 base does under your patio. It turns the whole patio into a giant drain field. Instead of trapping water, it gives the water a path straight down and out. Water that drains away can’t wash out a bedding layer, because it’s never sitting there pooling and running sideways to begin with.

The bedding stone on top matters just as much as the base under it. We use number 789 chip stone, that’s very specific and important. Chip stone is crushed, so every piece has jagged, sharp edges. When we run the plate compactor over it, those edges lock into each other like puzzle pieces and the whole layer knits together to make a very strong base. Rounded gravel, like the smooth stuff that people use in fish tanks, does the opposite. When you step on it your heel rolls the stones and leaves a divot. Jagged chip stone doesn’t roll. It grabs and holds, so the surface your pavers rest on stays put under foot traffic, furniture, and everything else you put on a patio.

Compaction is a very important step and there’s a right way and a wrong way to do it, which isn’t always obvious. We compact all four inches of the number 57 in just one single pass, not in multiple thin layers. Doing it in layers sounds like it would work better and be more careful, but it actually over-compacts the stone and crushes the bigger pieces down into smaller ones, which actually makes the base weaker. So we screed the stone, rake it level, and run the compactor just one time. After that, you could drive a truck across it without making any marks at all. Then the two inches of number 789 go on, we screed that as well, and then it gets compacted again. At that point the base is as solid as a concrete pad. Next we lay down the polymeric sand, which is joint sand mixed with a binder that hardens when it gets wet so it locks the joints in place instead of washing out. Then the pavers go right on top.

Sand Base vs. Gravel Base, Side by Side

Here’s a chart so you can easily compare everything at a glance. Read it as two methods that look identical the day the patio is finished and then split apart underground over the next few wet seasons. The numbers in the stone names, 57 and 789, are just standard size grades for crushed stone, nothing you need to memorize.

Do you see the pattern? The sand base only wins on price the day it’s installed. The gravel base comes out ahead every season after that.

When Is a Sand Base Actually Fine?

To be fair, sand isn’t the wrong choice for everywhere. On a high, dry lot with fast-draining soil and no major standing-water problems, a well built patio with a sand base can hold up for a long time. A lot of the country is built that way and it works well and lasts. The problem with sand is specific to our area. We have wet, slow-draining ground and tons of rain. A method that counts on water staying out of the bedding layer is a gamble in a place where the water doesn’t drain. That’s the whole reason we build patios the way we do here.

And not every uneven paver means the base was done wrong. A single low spot beside a downspout, or one paver that settled near an edge, can be a small drainage or edging fix, it doesn’t mean the entire base is failing. If a patio is only a year or two old and one corner dips, it’s worth a closer look before anyone assumes the worst. Our goal on a new build is simpler than chasing down problems on an old one: get the base right the first time, so you are not standing in your backyard in three years wondering why your patio moved.