Do Sandboxes Need a Bottom?

If you’ve shopped around for a sandbox, you’ve probably noticed that most pre-made sandboxes are built with a bottom or floor.

But if you’ve decided to build your sandbox yourself rather than purchasing one online or from a store, you may be wondering if it’s really necessary to add a bottom.

A sandbox doesn’t necessarily need a bottom, but having one is a good idea. Sandbox bottoms help reinforce the frame, making the sandbox itself more sturdy and secure. Not only that, a floor will help keep the sand cleaner and prevent weeds and bugs from coming up through the ground below.

Keep reading to find out what materials are best to use for sandbox bottoms and the other benefits they provide!

Sandbox Location

The first thing to consider when deciding whether or not to add a bottom to your sandbox is what kind of surface you’ll be putting it on. 

If you’re putting it on a concrete slab without a bottom, the sand will likely make its way underneath the frame, eventually pushing the frame up and allowing more sand to spill out – unless, of course, you intend to fix the frame to the concrete and seal the edges.

You’ll face a similar problem with a brick patio, only with more seams for the sand to escape through. And, of course, on wood decking, the gaps between the boards will leak just as much sand as you put in.

Putting the sandbox frame directly on dirt or grass out in the yard will allow you to sink the frame into the ground to some degree, which will help prevent sand from escaping around the bottom.

Many people even dig down a few inches and set the frame inside the hole, which helps reinforce the frame so it won’t come apart or bulge out over time.

But without a bottom of some kind, instead of sand getting out, other things can get in. Soil from below will get mixed in with the sand, insects may tunnel up from the ground, weeds and grass can sprout up through the dirt, etc.

As you can see, there are very few cases in which a bottomless sandbox frame will work well – which is probably why nearly all sandboxes on the retail market have a bottom or ground liner, whether they’re the smaller plastic variety or the more spacious wooden designs.

Benefits of Having a Sandbox Bottom

Putting a bottom or barrier under your sandbox is a good idea for several reasons. We touched on a few of them briefly in the previous section, but now let’s look at each one in turn.

1. Protects Against Weeds and Grass

Everyone knows that weeds are resilient and insidious, but not everyone realizes that they can thrive even in their dry sandbox – weeds that have begun to sprout in the soil can grow straight up through the light sand. In fact, they can take over an unprotected sandbox with astonishing speed. 

Similarly, when putting a sandbox on the lawn, it’s natural to assume that smothering the grass with a whole bunch of sand will kill the grass. But amazingly, grass can keep on growing even after having a few hundred pounds of sand dumped on it.

Naturally, this doesn’t apply if you put the sandbox on concrete or stone tiles – but if you’re putting it on dirt or grass, adding a bottom will help prevent your sandbox from becoming a garden of rogue plant life.

2. Protects Against Insects

Just as a bottom will protect your sandbox from unwanted vegetation, it will also protect it from unwanted pests that tunnel through the earth below.

Ants, in particular, will view a sandbox as a great place to set up shop. Of course, a bottom will only prevent bugs from coming up from the ground, not from anywhere else – but there are other ways to handle that.

3. Helps Keep the Sand Clean

As kids play and dig in a sandbox with no bottom, it’s only inevitable that the soil underneath will start to get mixed in with the sand – which means your kids will probably come out of the sandbox covered in dirt.

Organic matter like roots and grass may also make their way up from below. If you want your sandbox to have nothing in it but sand and toys, a bottom is crucial.

Also read: How to Sanitize Sandbox Sand

4. Keeps the Sand Contained

A bottom will also keep sand from escaping underneath the frame. The only other ways around this are to seal the bottom edges of the frame or build an in-ground sandbox.

5. Helps Reinforce the Frame

This really only applies if the bottom is made of wood or another sturdy material and is firmly attached to the frame, but it’s a huge benefit nonetheless. 

Over time, as the sandbox is exposed to the elements and the pressures of general use, the walls will likely start to bow out in the middle or come apart at the corners. If they’re securely fixed to a solid bottom, this is far less likely to happen. 

However, if you’re building an in-ground sandbox, the surrounding earth will reinforce and support the frame just fine, so a more flexible material should be used for the bottom.

What Should You Use for a Sandbox Bottom?

There are a few different materials you can use for the bottom of your sandbox, each with its advantages and drawbacks.

The most popular and effective materials are wood, landscape fabric, tarps, and plastic drop cloths. What to put under sandbox ultimately depends on your specific situation.

Wood

If you’re making an above-ground sandbox, wood is probably the way to go. On top of keeping out underground invaders and dirt, a sturdy wood bottom will give the sandbox a solid foundation and help keep the frame from bowing or coming apart.

The main drawbacks of wood are that it’s a little more expensive, more labor-intensive, and susceptible to warping and rot. It’s also not ideal for an in-ground sandbox because it will make the frame harder to level once it’s in the hole (plus, the reinforcement aspect will be unnecessary). 

You’ll also need to drill several small holes (about ⅛”) in a wooden bottom to allow water to drain out, but this isn’t exactly a drawback – just an important step!

As to the type of wood to use, there’s a fair amount of debate. Some use a single large sheet of plywood, some use several 2’x4’s, and others use tongue-and-groove floorboards.

Pressure-treated wood is more resistant to rot and warping, but some types may be unsafe for direct contact with children or pets, so make sure you do some research to make sure it’s safe. But as far as natural lumber goes, cedar tends to hold up the best in outdoor settings.

Landscape Fabric

Landscape fabric is a popular choice for sandbox bottoms because it’s fairly inexpensive, naturally has good drainage, and acts as an effective barrier against dirt, weeds, and pests.

The only potential drawbacks of landscape fabric are that it offers no frame support and may eventually get torn up by children’s digging toys, if they get down to the bottom.

Some kinds are tough enough not to rip, however, and you can always add more than one layer for good measure.

Plastic Drop Cloths & Tarps

A tarp or heavy-duty plastic drop cloth are perhaps the least expensive options for a sandbox bottom. They are very effective at keeping out unwanted pests and plants, and they’re also great for sand containment if stretched tightly around the bottom of the frame and securely fastened.

These also offer no frame support, but their biggest disadvantage is that it can be quite difficult to get them to drain properly.

Poking several holes will help, but unless the plastic or tarp is taut, smooth, and has a consistent slope down to the drainage holes, water will tend to collect in any pockets or ditches. 

Any standing water and long-term moisture in your sandbox can harbor bacteria and become a breeding ground for mosquitoes, so this is a pretty big drawback. Even if you try to keep your sandbox covered, all it takes is one pop-up storm to turn it into a swamp.

In Conclusion

All things considered, quality wood or landscape fabric are probably your safest bet when it comes to your sandbox bottom, depending on what kind of sandbox you’re building and where you’re building it.

And with all the advantages, putting any sort of bottom or barrier on your sandbox is well worth the effort!