We had a yard party with our fire pit out on the grass about a year ago, and didn’t put anything underneath to protect against the heat. The grass has onlyjust grown back!
Permanent fire pits have heat proofing built in, but freestanding models need to sit on a fire ring, cement pavers, a heat shield, or a fire-retardant mat to protect the patio or grass. For wood or trex decking, you’ll need a thermal barrier such as DeckProtect™ to ensure you don’t cause damage.
Let’s dive down into this subject in more detail, looking at what should sit under your fire pit based on the kind of surface you intended to use it on.
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What Do You Sit a Fire Pit On?
There are many safe ways to have the fire pit of your dreams – in the spot of your dreams – without harming your patio, deck, or lawn. For free-standing fire pits, you can add a fire ring, some cement pavers, a heat shield, or a fire-retardant mat. For built in fire pits, add a layer of heat absorbing materials, like rock.
Wood burning fire pits burn hotter than gas ones. Many fire pits are made of steel, which is an excellent conductor. The temperature underneath the fire pit will be almost as hot as the fire itself.
A small wood fire burns at 600° F. A roaring fire burns at 1,400° F. The hottest fire is when the flames die down and the fire has burned to embers. Then, it’s around 2,000° F.
Fire safety is always an issue with fire pits. There are several things to consider when locating your fire pit.
First, check with your homeowner’s association about their fire pit rules.
If your fire pit is wood burning, it should have no overhanging roofs or trees. No gazebo fabric to accidentally blow close to flames. Safety experts say your fire pit should be 15 feet or more away from anything that could catch fire – a storage shed, wooden fence, trees, or your house.
Any overhanging tree branches should be at least 10 to 15 feet away. Property lines should be at least 10 feet away.
If your fire pit is a gas-burning one, then the space restrictions are fewer. Gas fire pits don’t burn as hot, they don’t throw off sparks, plus they can be turned off with a switch. Gas pit tables are especially safe. Experts recommend that gas fire pits be located 10 feet away from your house.
Gas fire pits are OK under a gazebo or a roof if the roof is over 6 feet away. Just be sure you have plenty of fresh air around a gas fire pit.
No wobbling fire pits. You fire pit site should be level. If you don’t have a good level area, get out a shovel and make one. Try to locate your fire pit in the lee of the prevailing winds.
Keep these cheap safety precautions nearby: a fire blanket, a bucket of sand, a bucket of water or the hose, a dry chemical fire extinguisher , and – your cell phone in case you need to call for help.
Do You Always Need To Use a Fire Ring?
You always need to use something to protect your lawn, your deck, a cement patio, or a cement paver patio. Fire rings are one of the great choices.
If you have a concrete patio or a concrete paver patio, depending on the materials in the concrete pavers or bricks, it will either expand or contract with extreme high temperatures. The expansion and contraction lead to cracks, splits, and crumbling.
Extreme heat can change the chemistry of mortar. Without heat protection, eventually the pavers or bricks will have to be replaced.
A steel fire ring, filled with heat absorbing rocks and sand, will prevent heat damage to the wall materials. Fill the fire ring with stones and sand.
The heavy gauge steel fire ring also provides structural support for a ring of pavers or bricks. It helps keep your fire pit looking great.
Choose a fire pit ring with a large steel gauge. The higher the gauge (like 20), the longer it will last. Generally, if the fire pit ring is one welded piece, the better it will stand up to the extreme temperatures. The more pieces, the weaker the fire ring.
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How Do You Use a Fire Pit On Grass Without Killing it?
Grass will suffer or die under a fire pit. It’s called heat stress, and we’ve all seen it at the peak of summer, in a 100° F heatwave. Now consider that grass with 1,400° F heat.
Concrete pavers or patio slabs are a good idea for setting your fire pit on. Concrete won’t catch fire, plus they are heavy and sturdy enough to provide stability. Make sure the fire pit isn’t wobbly – check the level and dig them in if necessary.
Fire-resistant pit mats are a great solution out on grass. These heat-retardant barriers are available in many sizes and shapes. And they just roll up. Think – giant silicone mat. They don’t make solid, sturdy surfaces, but they are very versatile. Throw them in the back of the car for camping.
Pit mats wash up with soap and water. Pit mat manufacturers say that you should have no less than 4 inches between the mat and the bottom of the fire pit.
Heat shields reflect heat back up into the fire pit and away from whatever the pit is resting on. They are made of high-gauge metal and make sturdy, flat surfaces for portable fire pit legs. Some models claim to reflect 95% of the heat back up. They can weigh up to 25 pounds, which makes them luggable around the yard, deck, or patio.
Whatever you choose to use beneath your fire pit, it’s a good idea to move it around now and then – grass needs sunshine. For an added precaution against heat stress, and embers, water the grass around the fire pit before using it.
Will a Fire Pit Damage Concrete On a Patio?
Yup. It may be slow, but a fire pit will damage concrete over time. To prevent concrete from being damaged under your fire pit, you can use a pit mat, a fire ring, or a heat shield.
The good news is concrete won’t catch fire, like a wooden deck might. Concrete is 100% non-flammable. The bad news is that high temperatures make some materials in concrete expand – unless they contract.
Wood-burning fire pit temperatures can rise to a very toasty 2,000° F. That much heat will cause the concrete to dehydrate and spall or flake. Here’s a scary video on spalling from a concrete expert. Some materials in concrete (like limestone) will break down, making the concrete crack and fail.
Other materials – like quartz sand – expand in the heat, also causing cracking. That much heat will change the chemistry of the cement in the concrete (called calcination) and may turn the color slightly pink.
Finally, if you have gone the extra patio-building step and used rebar, then the results are worse. When rebar gets over 500° F, it gets brittle and starts to deform. If the rebar starts to deform, it will crack the concrete.
If you fire pit is built in, you may need to seal up cracks. Eventually, the cement around the pit will have to be replaced.
Can You Put a Fire Pit On a Stone Paver Patio?
A fire pit will damage and discolor stone. Rocks are tough, but not invincible.
The good news is rocks don’t catch fire. But extreme temperatures will weaken them. Extreme heat causes chemical changes in some rocks. There are many stone structure studies that show that stones can change color, spall, and crack after a fire.
Light-colored stones can become heavily discolored with soot.
Will a Fire Pit Damage Wood or Trex Decking?
Yup. Trex decking starts to soften at 176° F and wood ignites at 450° F – so you need some sort of heat shield under your fire pit on both surfaces.
Trex does not recommend placing a wood burning fire pit on top of Trex decking. They recommend a product called DeckProtect™. DeckProtect™ is a type of thermal barrier. It is made of volcanic rock fiber tiles in a heavy gauge aluminum frame. Heavy duty rubber feet keep the tray elevated above the deck, which prevents the deck from molding under the tray.
Final Thoughts
If you’ve got a permanent fire pit, then heat proofing will no doubt be built into the base.
However, if you’ve invested in a freestanding and portable model then you’ll need to stand your fire pit on a fire ring, cement pavers, a heat shield, or a fire-retardant mat – so it doesn’t damage your patio, pavers or grass.
For wood or trex decking, you’ll need a thermal barrier such as DeckProtect™ to – erm – protect your deck. 🙂
