When it’s time to build or install a fire pit, you’ll need to decide what type of rocks to put at the bottom. This choice is extremely important because every fire pit rock has the capability of exploding, some more than others. Luckily, there are several types of rocks that are safer than others.
The best types of rocks to use for fire pits that won’t explode as easily are granite, marble, slate, lava rocks, and fire glass. Lava rocks are popular because of their affordability and effectiveness. Fire glass is also popular due to its aesthetic appeal, lifespan, and heat displacement.
Rocks explode when the water that’s trapped inside them heats up until bursting, breaking them apart and possibly sending shards in every direction. This can be extremely dangerous, so it is important to choose ones that are non-porous or permeable so less water will be present. Keep in mind, however, that almost all rocks (especially the ones used for fire pits) have water in them, however very small in amount.
Luckily, there are several types of rocks that are safer to use in fire pits. Don’t be fooled, though, if every rock has water in it, then every rock can explode. Let’s look at the common types and how to keep them from exploding.
Types of Rocks to use in a Fire Pit with a small Chance of Exploding:
Lava Rocks
Many people swear by lava rocks for their natural beauty, safety, and effectiveness. They are capable of withstanding extremely high temperatures while also emanating a pleasant warmth and campfire feeling.
It’s no question why they can withstand more heat than other rocks. After all, they’re lava rocks, so they’re capable of handling molten lava temperatures, making them one of the safest rocks to use in fire pits (unless they’re wet!).
Many lava rocks are porous and therefore can explode easily if they get wet. Keep them dry at all times. If this is not possible, the rocks should be cured before allowing people near the fire pit.
Before using new lava rocks (even if they claim to be pre-cured), cure them by putting them into the fire pit and lighting it. Cover the fire with a metal grate and let it burn for up to 45 minutes. Stand 10 feet away. If there’s water trapped inside them, you’ll hear popping sounds. The goal is to let all of the water explode from the rocks until they are completely dry.
To keep lava rocks from getting wet after you’ve cured them, keep fire pits covered or lava rocks stored in a dry place when not in use. If they soaked, they’ll need to be cured again. If they just got slightly wet, let them dry out before starting a fire. For propane fire pits, keep the heat on low for half an hour to dry out the rocks before turning the heat up higher.
If you think you’ll have a hard time keeping lava rocks dry, consider fire glass as an alternative.
Fire Glass
Fire glass is an aesthetically pleasing albeit more expensive alternative to lava rocks that come in the form of many small glass crystals or smooth beads. They’re specially made for gas fire pits to withstand intense heat, hide the burner, and produce an array of sparkling colors as flames dance across them. Quite simply, they make fires more hypnotizing to look at.
Fire glass can explode. It’s less porous than lava rock and therefore harder to explode, but do not let fire glass get wet or it will crack. Make sure it’s dry before using and always choose fire glass that’s tempered.
Fire glass requires less fuel than other rocks because they distribute heat so well. This is because they come in smaller pieces and have many facets for heat to reflect off of. You can get similar heat distribution with lava rocks if you break them into smaller pieces, but that requires more work.
Do not use regular glass! Fire glass is the only type of glass that is safe to use near fire. Fire glass manufacturers tumble the crystals to get rid of sharp edges so they’re safe to handle. Regular glass may release toxic fumes, blacken, crack, or explode into shards that fly in every direction. Watch out for cheap fire glass, too, as they may contain pieces of plastic that will also release toxic fumes.
One problem you might come across with fire glass is discoloration from propane gas fires. This will dull the glass and make it less visually appealing. Fire glass will also make popping sounds if it comes in contact with water as pieces break apart. This is not uncommon in fire glass that is being used for the first time. Manufacturers recommend letting the glass burn for 15 minutes at a safe distance to allow any cracks to break apart completely.
Rocks to Use in a Fire Pit:
If you’re not using lava rocks or fire glass for your fire pit, choose non-porous rocks that are less likely to absorb water. The most popular non-porous rocks or composites used for fire pits are as follows.
- Marble
- Slate
- Granite
- Brick
- Concrete
Rocks to Avoid using in a Fire Pit:
Avoid using the types of rocks listed below in your fire pit because they are porous and therefore more likely to absorb water. Some of them, especially sandstone, have weaker bonds between layers that can also cause them to explode.
- Limestone
- Pumice
- Sandstone
- River rock
- Gravel
- Smooth rocks (indicates extensive water erosion)
Wrapping Up
Choosing the right rocks and maintaining them is essential for keeping your family safe around the fire pit. It’s true that all rocks can explode, but you dramatically reduce the chance of it happening by choosing non-porous and dry rocks like granite and marble.
If you can safely do so, dry damp rocks on low heat in the fire pit (covered with a metal grate!) until the sounds of popping and sizzling have stopped. Do not attempt this with very wet rocks as it will surely cause an explosion.
If you’re looking for smoldering heat that radiates around the fire pit without costing too much, lava rocks are right for you. They are porous and prone to exploding, but it’s easy to keep them dry.
For top-tier heat displacement and beauty in a variety of colors, fire glass is an excellent choice. They are less likely to explode than lava rocks but are more expensive.
No matter what rock you choose for your fire pit, always follow safety guidelines and use precaution so you and your family can enjoy the relaxing fire year after year. Stay warm!
