What to Put in the Bottom of a Fire Pit

Start With the Kind of Pit You Have

The question sounds like it has one answer, but a dug ring in the lawn, a steel bowl on legs, a block-built patio pit and a propane fire table have almost nothing in common underneath. Each has a different job for its bottom layer: drain rainwater, protect metal, let air in, or hold a gas burner's media. Find your pit in the list, then read its section; the wrong layer in the wrong pit causes more trouble than no layer at all.

• In-ground or ring pit on soil: a gravel base that drains, with the fire on top.
• Plain steel bowl without air holes: optional thin sand bed, emptied and dried often.
• Double-walled smokeless steel pit: nothing added; keep the bottom clear of ash.
• Masonry or block patio pit: a drained base under the fire area, as the builder designed it.
• Gas or propane fire pit: only the media the maker specifies, lava rock or glass, at the depth the manual gives.

In-Ground Pits: Gravel for Drainage

The Smokey Bear campfire guidance describes making a pit by digging down about a foot and ringing it with a metal fire ring or a circle of rocks. In a backyard that becomes a shallow dish in the ground, and after a hard rain a dish fills with water. A layer of gravel at the bottom gives that water somewhere to go, so the next fire is not lit on mud and wet ash.

Put the fire on top of the gravel, inside a steel ring if you have one. The ring keeps coals from rolling out and marks the edge for children; the gravel keeps the base from turning into a puddle.

Sand in a Steel Bowl: A Shield, Not a Drain

A thin layer of sand in a plain steel bowl takes the direct heat of the coals off the metal and makes the ash easier to scoop. The catch is water. Sand holds rain, and wet sand sitting against bare steel is how the bottom of a cheap bowl rusts through. If you use sand, use a bowl with a drain hole, keep it covered between fires, and empty and dry the sand now and then rather than leaving it to soak.

Sand is also not a way to put the fire out. The Smokey Bear guidance warns against relying on dirt or sand alone, because coals keep burning under the cover. Water and stirring put a fire out; the sand only sits underneath.

Smokeless and Double-Walled Pits: Leave the Bottom Clear

Double-walled smokeless pits work by drawing air in low and sending it up between the walls to burn off smoke near the rim. Breeo, one maker of these pits, explains that ash build-up can block the airflow in the bottom of the pit and make the fire less smokeless, and recommends cleaning out the pit after at least every three to four uses. Adding sand or gravel to that kind of pit does the same thing as ash: it covers the air holes.

So for these pits the right answer is nothing at all, plus a habit of emptying cold ash regularly. Read your own maker's instructions, since designs differ.

Bare Steel, Weathering Steel and Rust

Some pits are meant to be left bare. The same maker describes weathering, or corten, steel as engineered to develop an iron oxide patina that protects the pit from the elements. A pit like that does not need a sand bed to protect it, and the orange surface on a weathering steel pit is the finish doing its job, not damage.

Ordinary painted steel is different. Once the paint burns off the inside of the bowl, the bare metal rusts wherever water sits, and keeping it dry matters more than anything you put in the bottom. The full routine is in how to keep fire pit from rusting.

Lava Rock and Fire Glass Belong to Gas Pits

Lava rock and fire glass are media for gas and propane burners. They spread the flame and hide the burner, and the maker of each unit specifies which media to use, how much and how deep. Piling on extra, or swapping lava rock for glass, is a change to the appliance, not decoration. In a wood fire pit they add nothing but a layer to dig ash out of.

If your gas fire pit will not light or the flame looks wrong after you changed the media, that is a question for the manual first, and then for a technician.

Ash Is the Layer Nobody Plans For

Whatever the pit, the real bottom layer after a few fires is ash, and it holds water like a sponge. The NFPA asks that ashes be cool before they go into a metal container, and the U.S. Fire Administration's fireplace safety card adds a lid and a spot outside at least 10 feet from the home. Scoop the cold ash out after a few fires, store it properly and the pit drains, breathes and lasts longer.

Built-In Fire Pits

A block or stone fire pit built into a patio needs a base that drains and a fire area that can take the heat, and both are decided when it is built. If yours holds water after rain, has cracked blocks in the fire ring or loose cap stones, our outdoor fireplace service looks at it. The guide on where to put a fire pit in your backyard covers placement before you build.

Built-in pits are part of what our experienced crew inspects and repairs. Our family-owned company is local to Spring Hill and Proudly American; book a free inspection and the written estimate comes with it. If the fix is as simple as clearing a drain hole, you will hear that from a Proudly American crew before anything else.

Sources

• Smokey Bear wildfire prevention program: campfire safety: Dig down about 1 foot; metal fire ring or circle of rocks; do not extinguish a fire with just dirt or sand
• Breeo fire pit maker FAQ: Ash build-up blocks airflow in the bottom of the pit; clean out after at least every 3-4 uses; let ashes cool; corten patina and stainless steel
• NFPA heating safety tip sheet: Cool ashes into a metal container
• U.S. Fire Administration: fireplace and wood stove safety card: Metal container with a lid, outside at least 10 feet from the home
• U.S. Fire Administration: outdoor fire safety tips: Fire pits at least 10 feet from the home or anything that can burn