Enjoying a quiet evening with a bonfire in your backyard is one of life’s simple pleasures. But when it comes to safety and durability, can you build a fire pit on a concrete patio, or is that a bad idea?
Well, while it’s safe to build a fire pit on your patio, the concrete might suffer. High temperatures can lead to spalling and cracking, which might threaten the integrity of the patio. That said, you can protect the concrete by laying firebrick, cinder blocks, or an ember mat underneath.
So with that in mind, here’s what to consider when building a fire pit in your backyard.
What Happens to the Concrete Under a Fire Pit?
Building a fire pit on a concrete patio is a safe and practical option if you want that cozy backyard vibe.
You might be thinking that concrete can just handle the heat, unlike live grass that dies or dead grass that catches on fire. However, concrete can suffer physical and chemical changes based on its components and the amount of heat stress you subject it to.
Cracking/Spalling
Concrete is either silica/quartz-based or limestone-based. If your concrete patio is made of quartz-based concrete, you might want to avoid putting a fire pit over it altogether.
Quartz particles expand when subjected to huge amounts of heat. The expansion causes micro-cracks that end up flaking chunks of concrete in a phenomenon called spalling.
Limestone, on the other hand, breaks down when heated. This has a negative effect on the concrete structure that you notice in the long run, but the concrete doesn’t crack as readily.
Just be careful that even limestone concrete can also crack and spall when subjected to a fire pit.
Concrete always retains a moisture percentage because it never stops curing. The direct heat from the fire evaporates water from its deep layers, causing it to be brittle and flake off.
Calcination
In limestone-based concrete mixes, a chemical reaction called calcination can happen when you build a huge fire. At temperatures greater than 1,400° F, limestone disintegrates into lime and carbon dioxide.
The result of this chemical reaction appears as a white layer on top of the concrete that doesn’t wash or scrub off easily. While it doesn’t threaten its structural integrity right away, it looks unsightly, to say the least.
Discoloration
Due to the intense heat from the fire pit, concrete patios might get discolored and patchy. Whether the ashes darken some spots or the area under the fire pit gets a pinkish hue, you’re still getting variation you didn’t ask for.
That’s why you should always protect your concrete patio before you build a fire pit. Thankfully, it’s not at all a difficult process!
How to Protect a Concrete Patio From a Fire Pit
If you want the pros of a backyard fire pit without the cons of a damaged concrete patio, here’s what to do:
Build a Cooler Fire
Small fires are less hot than larger fires. So, to protect the concrete from the negative effects of a fire pit, try to downsize the fire you’re building and use less fuel.
On that note, the fuel you use affects how hot it becomes as it burns. Wood is the least hot fire fuel, reaching from 600 to 1,200° F, while coal, gas, and propane fires can easily cross 1,500° F.
Use a Protective Layer
If you intend to use a metal fire pit that you can move wherever you want, then this tip should help you make the most of it. While elevated above the ground, the heat radiating from the fire pit can still singe the concrete unless you use a barrier.
Ember Mats
These fire-proof pieces of cloth protect the area right underneath them from falling embers and can withstand high temperatures. Just keep in mind you should place the fire pit at least 10 inches above the ember mat to prevent any heat transfer to the concrete.
Pavers
You can use a layer of pavers as a protective measure against concrete damage. Concrete pavers, cinder blocks, or fire bricks are all excellent choices to avoid the negative effects of direct heat on your patio.
The best part is that you can replace the pavers once they get discolored or cracked and use new ones. That way, you’re ensuring both high aesthetics and functionality.
Use a Metal Fire Pit
If you’ve decided that you don’t want a permanent fire pit on your concrete patio, then a movable metal fire pit is your friend. You just have to follow the correct process when you’re using it.
Place a layer of pavers followed by an ember mat, then you can place the metal fire pit on top. The following day, move the fire pit to a new spot before you light it to avoid direct heat on just one spot.
Final Thoughts
Can you build a fire pit on a concrete patio?
Yes, you can, but with a few caveats. You need to protect the concrete by placing pavers followed by an ember mat. Moving the fire pit around also helps prevent heat stress in one spot. Lastly, a smaller, cooler fire is less likely to damage your concrete patio than a larger one.
Ben has a bachelor’s degree in construction engineering. When not constructing or remodeling X-Ray Rooms, Cardiovascular Labs, and Pharmacies, you can find him at home with wife and two daughters. Outside of family, He loves grilling and barbequing on his Big Green Egg and Blackstone Griddle, as well as working on projects around the house.
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