Fire pits are a great heat source for everything from barbecues to make-shift home camping. You’re probably considering adding a portable fire pit to your backyard. Because you’ve got a concrete patio, you’d like to know what effect the fire pit will have on it.
Portable fire pits damage concrete with time. The materials within concrete lose water, expand, and crack when exposed to heat from a fire. Rebars supporting concrete patios also become deformed when heated. Luckily, it’s possible to evade the damage that concrete sustains from portable fire pits.
I’ll illustrate the factors that contribute to portable fire pits spelling trouble for concrete surfaces. Afterward, we’ll explore some preventative measures you can take to keep your concrete looking as good as new while you enjoy your portable fire pit.
Concrete Can’t Take the Heat
Concrete is an excellent base material for a portable propane fire pit. Since concrete is non-combustible, you would struggle to find a more suitable location for a fire pit.
Concrete isn’t immune to heat damage, though. Portable fire pits typically burn between 450 °F (232 °C) and 2,000 °F (1,093 °C). These values are significantly higher than concrete’s threshold of significant degradation (150-200 °F, or 65-93 °C).
One common assumption is that concrete will be fine under portable fire pits because they aren’t directly on the ground. This school of thought is false.
Usually, portable fire pits have an elevation of 12-14 inches (30-35 cm) from the ground. At its hottest, the searing fire from the fire pit will still wreak havoc on the concrete underneath it from this distance.
Here are some ways that heat makes concrete deteriorate:
Dehydration Causes Cracking
Concrete consists of portland cement (10-15%), air and water (15-20%), and aggregates like crushed stone, gravel, or sand. When the cement and water interact, they’ll toughen and secure the aggregates to form the rock-like solid we call concrete.
Heat has an undeniable effect on water–enough heat makes the water vanish. Dehydration occurs when the scorching fire pit’s heat interacts with a concrete surface. After the water leaves, pockets of space remain within the concrete, a vacuum that lays the ground for cracking.
Damage Depends on Aggregates
The type of damage sustained largely depends on what aggregate created the concrete.
If limestone was the aggregate, then the concrete cracks and warps. However, the more common aggregate for concrete manufacturing is quartz. Comparatively, quartz boasts a higher tolerance to heat. Along with its hardness, this explains its desirability over limestone.
With that in mind, I would be remiss if I didn’t point out that concrete infused with quartz expands rapidly and spontaneously. As such, the cracking that occurs to this kind of concrete will be more dramatic and extensive.
Consequently, you’ll want to place your portable fire pit on a limestone-based concrete surface. Of course, this measure will only delay the inevitable heat damage.
In addition to the limestone cracking, calcination will further disfigure the concrete with white streaks.
Calcination is a perfect example of a double-edged sword. The chalky layer on the concrete is ugly; no one wants to see blemishes on their concrete, after all. However, it also offers extra insulation for your future barbecues. (Considering how tricky it is to get rid of, you’re lucky it has at least one benefit.)
With this information, you can choose what type of concrete you wish to have on your patio. Information about the aggregate incorporated should be available on the ready-mix bag.
Rebars Exacerbate Destruction
Steel rebars reinforce some concrete yards. While this is a phenomenal idea structurally, rebars are prone to damage from portable fire pits.
Rebars become brittle when exposed to temperatures as low as 500 °F (260 °C). Anything above 1,300 °F (704 °C) would weaken the steel rebar by a whopping 20%.
Additionally, blistering heat quickens the reaction between the steel and the concrete’s aggregates, which results in the metal’s degradation and subsequent cracking.
Safeguarding Your Concrete Space
Mitigating the harm that heat from a portable fire pit causes is beyond achievable. Here are some steps you can take to safely enjoy your portable fire pit while steering clear of damage to your concrete:
Periodically Change the Portable Fire Pit’s Location
A good first move you can make is to take advantage of the fire pit’s portability.
Using it in different sections within your yard will effectively spread the heat’s concentration around a wide area. This intervention doesn’t entirely save the concrete from deterioration, but it’s significantly better than setting the fire pit in one place indefinitely.
You should ensure that the fire pit has cooled down before touching it. And, even as you transfer it from place to place, make sure that these places are concrete-based. Surfaces like grass and wood are flammable, presenting a safety hazard. Further, they would suffer more ruin than concrete.
Cover the Concrete Surface
Many people have valid reservations about changing the location of their portable fire pits. Maybe moving it would ruin the look you’re going for in your backyard. Or perhaps placing the fire pit anywhere else would be more dangerous due to restrictions in your environment.
If this sounds like you, let me introduce you to pavers, ember mats, and fire pad protectors.
Pavers are concrete bricks that protect the surfaces under them from heat damage. Concrete’s non-flammability shines through here as well. Here’s an article we wrote about whether you can put a fire pit on top of pavers.
With time, pavers will get dehydrated and crack. They are concrete blocks, after all. However, your concrete yard under them will be as safe as a tortoise in its shell. Replacing pavers is super cheap, which elevates their usability as shields for your patio.
For the aesthetically minded fire pit owners, pavers present an opportunity to decorate your space further. You can arrange them unassumingly, enabling them to accentuate your backyard while protecting the concrete.
Fire bricks are additionally applicable as concrete surface liners. As a result of being made of clay, fire bricks boast a higher tolerance to heat than their concrete counterparts.
Ember mats act as barriers between fire pits and the surfaces beneath them.
Their functionality is multipronged–they’ll keep any dropping embers, charcoal, or grease from messing up your concrete.
Thanks to their fiberglass and silicone exterior, ember mats are a breeze to clean, an aspect that will appeal to those who hate sweeping up pavers.
They are more costly to replace, though. And you’ll need to replace them relatively frequently as they aren’t nearly as rugged as pavers or fire bricks.
Fire Pad Protectors
These aluminum devices take patio preservation to the next level. They’re supposed to be placed about 6 in (15 cm) under the heat source. Then, the magic happens.
According to Newtex, their iteration of this protector reflects about 95% of the heat back to the fire pit, transforming it into a foolproof fire barrier.
To optimize their reflective properties, you’ll need to get any falling embers off such fire pad protectors frequently.
Crank Down the Heat
If you’re opposed to any of the above measures, you can always use smaller fires on your portable fire pit. A reduced fire will still do most things you need it to do, all while extending your patio’s lifespan.
Unfortunately, you will still have to reckon with gravity. Grease, charcoal, and embers are bound to fall on your concrete surface.
The high temperature emitted from a portable fire pit gradually damages concrete. Factors like the kind of aggregate and the presence of rebars determine just how bad the destruction will be. Fortunately, you can take several preventative measures to retain your concrete’s flawless look.