The BrickWood Fire Brick Guide
Fire Brick: The Complete Guide to Refractory Brick for Pizza Ovens, Fire Pits and Forges
What fire brick is, how it differs from regular brick, which grade and size you need, how many to buy, which mortar to use, and how to make it last. Written in plain English for first-time buyers.
Fire brick is a heavy, heat-proof brick made from a special clay called fireclay and baked in a kiln, so it can be heated and cooled over and over without cracking. BrickWood's full-size fire brick measures 9 x 4½ x 2½ inches, weighs about 7.65 pounds, and is a medium duty brick rated to 2,700°F. That's far hotter than any pizza oven, fire pit or fireplace will ever get, which is why fire brick is the go-to material for lining pizza ovens, fire pits, fireplaces, forges, smokers and kilns.
We've helped thousands of backyard builders since 2013, and we ship fire brick by freight to job sites all over the country, with FREE shipping anywhere in the U.S. Most of the people who call us have never bought fire brick before, so this guide skips the jargon. When we do have to use a technical word, we explain it right there.
Building a pizza oven? Before you buy a single brick, download the FREE step-by-step pizza oven plans. Every BrickWood plan comes with a complete materials list, so you'll know exactly how many fire bricks your oven needs.
Fire Brick: Quick Answers
- What it is: a brick made from fireclay and fired in a kiln so it survives repeated high heat. It's also called firebrick, refractory brick or fireclay brick.
- Standard size: 9 x 4½ x 2½ inches, called a "full size" or "straight." Thinner 1¼-inch fire brick splits are also available.
- Grade: medium duty fire brick (rated to 2,700°F) is the right choice for pizza ovens, fire pits, fireplaces and most hobby forges.
- Hard vs. soft: use hard (dense) fire brick anywhere fire, food or tools touch it. Soft (insulating) brick is for insulation only.
- Weight: about 7.65 lb per brick, so our 160-brick minimum order weighs about 1,225 lb.
- Ordering from BrickWood: sold by the brick with a 160-brick minimum (enough for a Mattone Barile oven and base) and FREE shipping in the U.S.
- Regular brick: don't use regular red clay brick, concrete pavers or concrete block where they touch fire. They crack, flake and can pop apart.
- Mortar: outdoors, use only non-water-soluble high-heat mortar, either BrickWood Refractory Mortar or our homemade recipe of 3 parts sand, 1 part lime, 1 part fireclay and 1 part Portland cement.
- Insulation: fire brick stores heat; it doesn't insulate. A pizza oven also needs ceramic fiber blanket insulation.
Part 1 • The Basics
What Is Fire Brick?
Fire brick is a brick built to live in fire. It looks a lot like an ordinary brick, but it's made from different ingredients and baked at much higher temperatures, so it can take the heat of a wood fire, cool down overnight, and do it all again the next day, for years.
You'll see it called by several names, and they all mean the same thing to a backyard builder:
- Fire brick or firebrick (one word or two, both are correct)
- Refractory brick ("refractory" simply means heat-resistant)
- Fireclay brick (named after the clay it's made from)
- Kiln brick or oven brick (named after where it's used)
What is fire brick made of?
The main ingredient is fireclay, a natural clay that's rich in two heat-loving minerals: alumina (aluminum oxide) and silica (the same mineral that makes up most sand). Ordinary brick clay contains more iron and other minerals that melt or weaken at lower temperatures. Fireclay has fewer of them, so it stays strong when things get hot.
Manufacturers grind the fireclay, mix in grog (clay that's already been fired and crushed, which keeps the brick from shrinking and cracking), press it into shape, dry it, and fire it in a kiln for about two days. The heat fuses the clay particles together into a hard, stone-like block. In general, the more alumina a brick contains, the hotter it can handle. That's the basis of the grading system we cover further down.
What is fire brick used for?
Anywhere a fire needs a tough, heat-proof lining. For homeowners, that usually means:
- Wood-fired pizza ovens: the cooking floor and the walls and ceiling of the oven
- Fire pits: a liner that protects the outer block or stone from cracking
- Outdoor and indoor fireplaces: the firebox lining
- Blacksmith forges: the forge floor and the area around the fire
- Smokers, barbecue pits and outdoor kitchens: fireboxes and heat-proof hearths
- Kilns, wood stoves and boilers: linings and replacement liner bricks
Fire brick words in plain English
You'll run into these terms when you shop. Here's what they actually mean.
| Term | What it means |
|---|---|
| Refractory | Heat-resistant. Refractory materials keep their strength at temperatures that would ruin ordinary building materials. |
| Fireclay | The heat-resistant clay fire brick is made from. Bagged fire clay is also an ingredient in homemade high-heat mortar. |
| Alumina | A heat-resistant mineral in fireclay. More alumina usually means a higher temperature rating. |
| Duty grade | The fire brick rating system: low, medium, high and super duty. It tells you how much heat a brick is built for. |
| Hard (dense) fire brick | Heavy, solid fire brick that stores heat and stands up to fire, tools and food. This is what pizza ovens, fire pits and forge floors use. |
| Soft (insulating) fire brick | Lightweight brick full of tiny air pockets, also called IFB. It blocks heat instead of storing it. Used in kilns and as backup insulation. |
| Thermal mass | A material's ability to soak up heat and slowly give it back. Fire brick has a lot of it, which is why a brick oven stays hot for hours. |
| Thermal shock | The stress a material feels when it heats up or cools down quickly. Fire brick is made to survive it; regular brick isn't. |
| Spalling | When the face of a brick cracks and flakes off. It's the classic way regular brick fails in a fire. |
| Straight | A standard rectangular brick. A full-size straight is 9 x 4½ x 2½ inches. |
| Split | A thinner fire brick, usually 1¼ inches thick, used for liners. See our fire brick splits. |
| Refractory mortar | Heat-resistant "glue" that bonds fire bricks together. Regular mortar isn't made for oven heat. |
| Non-water-soluble | Won't dissolve or wash out when it gets wet. Outdoor ovens and fire pits need non-water-soluble mortar. |
| Castable refractory | Heat-resistant cement you mix with water and pour or pack into a form, like concrete for high heat. See our castable refractory cement. |
| Ceramic fiber blanket | A fluffy, high-temperature insulation blanket wrapped around a pizza oven or used to line a forge. See our ceramic fiber blanket. |
| Curing | Drying out a new oven or fire pit with a series of small fires before you build a big one. |
Fire Brick vs. Regular Brick: Why Regular Brick Fails in a Fire
This is the question we hear most: "Can I just use regular brick?" For anything that touches the fire, the answer is no.
A regular red clay brick may survive a fire or two, and some can handle around 1,200°F. The problem isn't one fire. It's hundreds of them. Every time you light a fire, the face of the brick heats up fast while the inside stays cooler. The hot side expands, the cool side doesn't, and that tug-of-war puts stress on the brick. When the fire goes out, the whole thing happens again in reverse. That's thermal shock.
Fire brick is made to handle that cycle over and over. Regular brick isn't. Over time it cracks, the face flakes off (that's spalling), and it gets weaker and crumbly. In a pizza oven, those flakes can end up on your food.
Why concrete pavers, block and river rocks are even worse
Concrete pavers, cinder block, retaining wall block and stones from a river or creek can hold moisture deep inside. When a fire heats that water, it turns to steam. If the steam can't escape fast enough, the material can crack loudly or pop apart and throw sharp pieces. Never use them where they face the fire.
"Fired clay" is not the same as "fireclay"
Every regular brick is fired in a kiln too, so a label that says "kiln-fired clay brick" doesn't make it a fire brick. What matters is what the brick is made of and what it's rated for. A real fire brick has a duty grade and a temperature rating.
Where regular brick and block are fine
- The base or stand your pizza oven sits on
- The decorative outside of an oven, fireplace or fire pit, as long as fire brick faces the flames
- The outer wall of a fire pit, behind a fire brick liner
Hard vs. Soft Fire Brick: Dense vs. Insulating
There are two very different kinds of fire brick, and buying the wrong one is one of the most common mistakes we see.
Hard fire brick (also called dense fire brick or hard brick) is heavy and solid. It soaks up heat, stores it, and gives it back slowly. It also has a tough surface that holds up to metal pizza peels, ash rakes, cast iron pans, hot coals and steel being dragged across a forge. BrickWood fire brick is hard, dense, medium duty fire brick.
Soft fire brick (also called insulating fire brick, or IFB) is made with sawdust or other fillers mixed into the clay. The filler burns away in the kiln and leaves the brick full of tiny air pockets, a bit like a sponge. Air doesn't carry heat well, so soft brick is a great insulator, but it stores very little heat and its surface is soft enough to scratch with a fingernail.
| Hard (dense) fire brick | Soft (insulating) fire brick | |
|---|---|---|
| Weight (full size) | About 7 to 8 lb (BrickWood: about 7.65 lb) | About 2 to 3.5 lb |
| Job | Stores heat and takes abuse | Keeps heat from escaping |
| Surface | Hard and tough | Soft and easy to gouge |
| Cutting | Wet saw with a diamond blade | An ordinary hand saw works |
| Pizza oven floor and walls | Yes | No |
| Fire pit liner | Yes | No |
| Forge | Floor and fire area | Some small propane forges |
| Kilns | Floors, fireboxes, flame areas | Electric kiln walls, backup insulation |
The quick test: pick it up. A dense fire brick feels like a regular brick or heavier. An insulating brick feels surprisingly light for its size, and you can scratch it with a key.
Both kinds are real fire brick. Soft brick isn't "fake." It's just built for a different job. For anything you cook on or build a fire against, you want hard, dense fire brick.
Fire Brick Grades Explained: Low, Medium, High and Super Duty
Dense fire brick is sold in duty grades. The grade tells you roughly how much heat the brick is built for, and it mostly comes down to how much alumina is in the clay. In the U.S., these grades come from an industry standard called ASTM C27, so a "medium duty" brick from one maker is built for the same job as a "medium duty" brick from another.
| Grade | Rated to about | Alumina | Typical uses |
|---|---|---|---|
| Low duty | 1,750°F | 24 to 26% | Fireplace chimneys and mild heat. Not recommended for pizza oven floors. |
| Medium duty | 2,700°F | 34 to 38% | Pizza ovens, fire pits, fireplaces, smokers, most hobby forges. The best all-around choice for homeowners. |
| High duty | 2,850°F | 36 to 40% | Boilers, industrial kilns and higher-heat equipment |
| Super duty | 2,900°F | 40 to 44% | High-fire kilns and demanding industrial use |
| High-fired super duty | 3,000 to 3,150°F | 40 to 44% | Fired longer for extra density; continuous industrial furnaces |
| High alumina | 3,000°F and up | 50 to 90%+ | Steel mills, chemical plants, reactors. Overkill for any backyard project. |
Which grade do you need?
For a pizza oven, fire pit, outdoor fireplace or smoker, medium duty dense fire brick is the sweet spot:
- Plenty of heat margin. It's rated to 2,700°F. The hottest part of a pizza oven floor, right under the flames, runs about 1,200 to 1,400°F.
- The right balance. It stores heat well, stands up to tools and thermal shock, and handles years of firing.
- Better value. High and super duty brick cost more and won't make better pizza. You'd be paying for heat your oven will never reach.
Higher grades earn their price in places that run much hotter for much longer, like high-fire pottery kilns and industrial furnaces. We cover those in other uses below.
How hot can fire brick get?
The temperature on a fire brick is its maximum service temperature: the most heat it's designed to handle in normal use. It's a ceiling, not a target. Here's how that compares with real projects:
- Pizza oven: the cooking floor runs about 650 to 800°F for Neapolitan-style pizza, and the floor under the flames can reach 1,200 to 1,400°F.
- Fire pit and fireplace: a hot wood fire runs roughly 1,000 to 1,500°F, with hotter spots in a deep bed of coals.
- Blacksmith forge: forging steel takes roughly 1,700 to 2,300°F, and the hot spot of a forge can run higher when you're welding.
- Pottery kiln: stoneware firings reach roughly 2,200 to 2,350°F and hold there for hours.
Medium duty fire brick covers pizza ovens, fire pits and fireplaces with room to spare. Forges and kilns get closer to the line, so we cover them in their own sections. One more thing: smoke, ash and chemicals like forge flux can lower how much heat a brick handles in real life, which is another reason to keep a healthy margin.
Part 2 • Planning Your Order
Fire Brick Sizes and Shapes
The standard U.S. fire brick is the full-size straight: 9 x 4½ x 2½ inches. It's the size almost every pizza oven, fire pit and kiln plan is drawn around, and it's the size BrickWood sells. It's big enough to store a lot of heat, small enough to handle with one hand, and it lines up with the standard sizes of other masonry.
| Shape | Common size (inches) | What it's for |
|---|---|---|
| Full-size straight | 9 x 4½ x 2½ | The standard brick for pizza ovens, fire pits, fireplaces and forges. BrickWood full-size fire brick |
| 3-inch straight | 9 x 4½ x 3 | Industrial furnaces; fewer joints in big walls |
| Split | 9 x 4½ x 1¼ (also 1, 1½ and 2 thick) | Thin liners for fireplaces, wood stoves and tight fire pits. BrickWood fire brick splits |
| Soap | 9 x 2¼ x 2½ | Half-width brick for narrow spots |
| Other straights | 8½ x 4½ x 2¼, 9 x 4 x 2½, 12 x 4½ x 3, 13½ x 4½ x 3 | Regional sizes and specialty equipment |
| Square-edge tile | 12 x 12 up to 24 x 12, 1½ to 3 thick | Large flat floors and hearths |
| Arch, wedge, key and skew | Tapered versions of a straight | Building curves, domes and the corners where an arch meets a wall |
Why thickness matters
A thinner brick stores less heat. A 1¼-inch split holds about half the heat of a 2½-inch full-size brick, so it heats up faster but also cools down faster. That's great for a wood stove liner, but a pizza oven needs enough mass to bake pizza after pizza, so oven floors and walls use full-size brick. If your plans call for 2½-inch brick, don't swap in splits or 3-inch brick. It changes the size and shape of everything you build on top.
Measure before you build
Sizes can vary a little from one manufacturer to another, and "standard" doesn't mean the same thing at every store. Measure a few bricks before you start, and don't mix brands on a cooking floor. A difference of even ⅛ inch leaves a lip that catches your pizza peel.
How Much Does a Fire Brick Weigh?
A BrickWood full-size fire brick weighs about 7.65 pounds. Most dense full-size fire brick lands somewhere between 7 and 8 pounds. For comparison:
- Fire brick split (9 x 4½ x 1¼): about half as much, roughly 3.9 lb
- Insulating (soft) fire brick, full size: about 2 to 3.5 lb
- Our 160-brick minimum order: about 1,225 lb, or a little over half a ton
- A full pallet of 456 fire bricks: about 3,500 lb, or roughly 1¾ tons
That weight matters in three places:
- Delivery. An order of 160 or more fire bricks travels palletized by freight truck, not by parcel service. Shipping from BrickWood is FREE anywhere in the U.S. Plan where it can be set down and how you'll move the bricks from there.
- Hauling it yourself. 160 bricks is already more than half a ton, and a full pallet is beyond what most half-ton pickups can safely carry. Check your truck's payload rating before you load it.
- Your base. A pizza oven's base has to carry the fire brick plus the insulation, finish and chimney. Build it to the plans. Our guide on how to build a pizza oven base walks through it.
How Many Fire Bricks Do You Need?
For a BrickWood pizza oven, use the materials list in your plans. It's figured for your exact oven, including the floor, walls and chimney opening. As a guide, a Mattone Barile oven and base takes 160 full-size fire bricks, which is exactly why our minimum order is 160. The larger Mattone Barile Grande kit includes 190. Building a 28-inch Mattone Cupola? It needs fewer fire bricks, so contact us and we'll ship the exact number your oven needs. Building a Cortile Barile? Its cooking floor takes only a small number of fire bricks, so most builders pick them up locally when they buy their other supplies. Use our masonry supply store finder. Get the FREE plans to see the full list for each oven.
For your own design, here's the simple math:
- Laid flat (the big 9 x 4½ face up), one brick covers about 40½ square inches. That's about 3.6 bricks per square foot.
- Laid on edge (the 9 x 2½ face up), one brick covers 22½ square inches. That's about 6.4 bricks per square foot.
Two quick examples
- A 36 x 36-inch oven or hearth floor is 9 square feet. Laid flat, that's 9 x 3.6 = about 32 bricks.
- A fire pit liner with a 36 x 36-inch opening, built 5 courses tall (about 12½ inches) with bricks laid flat, takes about 18 bricks per course, or about 90 bricks for the walls. Add about 32 more if you want a fire brick floor.
Then add a little extra. Plan on roughly 10% more for cuts and the occasional broken brick, unless your materials list already includes extras. We also recommend setting aside 10 spare fire bricks after your build. Store them somewhere dry, and you'll have perfect matches if you ever need to replace one.
Fire Brick Splits (9 x 4½ x 1¼ Inches)
A fire brick split is a full-size fire brick made half as thick: 9 x 4½ x 1¼ inches instead of 9 x 4½ x 2½. It's made from the same fireclay, in the same medium duty grade, with the same 2,700°F rating. The real difference is thickness. A split weighs about 3.9 pounds, roughly half as much as a full-size brick, and it stores about half as much heat.
BrickWood sells splits right here on this page, at the same price per brick as our full-size fire brick, with a 325-split minimum order. To order, choose Split under Size at the top of the page.
What fire brick splits are used for
- Wood stoves and fireplace inserts. Most stoves are lined with 1¼-inch splits. When you replace them, match the size your stove maker calls for.
- Fireplace fireboxes where full-size brick would take up too much room.
- Thin fire pit liners where there's only about an inch of space inside the outer wall.
- Forge floors. A split makes a cheap, replaceable floor that you can swap out when flux glazes it.
Don't build a pizza oven with splits
- A pizza oven floor and arch need the heat storage of full 2½-inch brick to bake pizza after pizza. Splits heat up fast, but they cool down fast too.
- BrickWood plans are drawn around full-size fire brick. Swapping in splits changes the size of everything you build on top.
Why do fire brick splits cost the same as full-size fire brick?
It's the question we hear most about splits: if a split is half the clay, why isn't it half the price? The short answer is the mold, not the clay.
Every fire brick is pressed in a heavy steel mold, and a mold for a single brick size costs a manufacturer $50,000 or more. That cost has to be paid back by the bricks that come out of it.
- Full-size fire brick is the most common fire brick there is. Factories press it by the millions, so the cost of the mold is spread across so many bricks that it adds almost nothing to each one.
- Splits are a specialty size. They need their own mold, which costs just as much, but only a small fraction as many splits are made and sold. The manufacturer still has to earn back that $50,000, and with far fewer bricks to spread it across, each split carries a much bigger share of the cost.
Here's a simple example with round numbers. If a $50,000 mold presses a million full-size bricks, it adds about a nickel to each brick. If a $50,000 split mold presses only 50,000 splits, it adds about a dollar to each split. The clay you save by making the brick thinner gets used up paying for the mold.
On top of that, a split goes through the same pressing, drying, kiln firing and handling as a full-size brick, so those costs don't get cut in half either. That's why splits cost about the same per brick as full-size fire brick nearly everywhere you shop, and why ours are priced the same as our full-size brick.
Part 3 • Fire Brick by Project
Fire Brick for Pizza Ovens
A wood-fired pizza oven is the most demanding job most homeowners will ever give a brick, and it's where fire brick really shines. Here's what the brick is doing while you cook:
- It stores heat. While the fire burns, the floor and walls soak up heat. That stored heat is what bakes pizza after pizza without the oven cooling off.
- It cooks the crust from below. The hot floor passes heat straight into the bottom of the dough. That's how you get a crisp, leopard-spotted crust in about 90 seconds.
- It cooks the top from above. The hot ceiling radiates heat down onto the toppings, while hot air rolls across the top.
- It takes a beating. The floor sees 750°F cooking temperatures, flames reaching 1,200 to 1,400°F, steam from wet dough, metal peels, cast iron and coals being pushed around, every time you cook.
Only properly made dense fire brick handles all of that at once.
How fire brick goes together in a BrickWood oven
Our BrickWood pizza oven kits make laying fire brick simple, even if you've never done masonry. On the Mattone Barile and Mattone Barile Grande, you lay full-size fire brick over a foam form that shapes the arch for you, so you get a perfect barrel-shaped oven without building a wooden arch frame or guessing at the curve. The Cortile Barile pairs a castable refractory shell with a full-size fire brick cooking floor. Not sure which oven fits your yard? Compare them in our pizza oven kit comparison.
Fire brick needs insulation
Fire brick stores heat, but it doesn't stop heat from escaping. Without insulation, the heat you worked to build up leaks straight out through the walls and into the base. That's why a wood-fired oven needs two kinds of insulation:
- Around the oven: ceramic fiber blanket wrapped over the fire brick. It's our number one recommended add-on, and it's required when you build a wood-fired oven.
- Under the floor: an insulating layer between the fire brick floor and the concrete, such as the layer called for in your plans. Some builders mix vermiculite or perlite with cement to make an insulating slab.
Learn more about how it works and how to install it on our ceramic fiber blanket insulation page.
Tips for a great fire brick cooking floor
- Use your flattest, best-looking bricks for the floor, and save chipped ones for cuts.
- Set the floor dead flat and check it with a straightedge. A lip of even ⅛ inch will catch your peel.
- Keep mortar and cutting slurry off the cooking surface.
- Follow your plans for how the floor is laid. Don't improvise the floor thickness or swap in thinner brick.
Fire Brick for Fire Pits and Outdoor Fireplaces
Most backyard fire pits are built from concrete wall block, pavers or stone. Those look great, but as we covered above, they aren't made to face a fire. Over a season or two, the inside face can crack, crumble or pop. Lining the inside of the pit with fire brick puts a heat-proof layer between the flames and the outer wall, so your fire pit lasts for years instead of a couple of summers.
How to line a fire pit with fire brick
- Start with drainage. Set the pit on a few inches of compacted gravel so rainwater can drain away instead of soaking the bricks.
- Build the liner inside the outer wall. Lay full-size fire brick flat for a thick 4½-inch liner, or stand them on edge for a thinner 2½-inch one. Where space is tight, fire brick splits make a 1¼-inch liner.
- Use high-heat mortar on the fire brick, not regular mortar. Outdoors it must be non-water-soluble. Our homemade recipe or BrickWood Refractory Mortar both work.
- Leave a weep gap or two in the bottom course so water can drain out of the pit.
- Add a floor if you like. Fire brick laid flat over the gravel makes a clean, easy-to-shovel floor.
- Cure it gently. Let the mortar set for a few days, then start with a few small fires before you build a big one.
Outdoor fireplaces
The same idea applies to an outdoor fireplace. The outer structure can be block, stone or brick veneer, but the firebox, the part that holds the fire, should be lined with dense fire brick and laid with high-heat, non-water-soluble mortar. Many builders use full-size brick for the back and floor of the firebox where the fire hits hardest. Always check your local fire codes for clearances to your house, fences and trees.
- Back wall and floor: full-size fire brick, because that's where the fire sits and the logs land.
- Side walls: full-size brick or splits, depending on how much room your design allows.
- Behind the fire brick: regular block or brick is fine, since the fire brick takes the heat.
- Before the first big fire: let the mortar set for several days, then cure it with a few small fires.
Fire Brick for Forges
Blacksmiths and knife makers use fire brick in almost every kind of forge. A forge runs much hotter than a pizza oven (roughly 1,700 to 2,300°F to work steel), so it's worth knowing where each type of brick belongs.
Coal and charcoal forges
In a coal or charcoal forge, the fire sits in a fire pot or on a forge table, and dense fire brick lines the area around the fire. Hard brick is the right choice here: it handles direct coals, the bump and scrape of tongs and steel, and the clinker you knock out of the fire. Full-size bricks laid flat make a sturdy, replaceable forge bed.
Propane (gas) forges
Most propane forges have a steel shell lined with ceramic fiber blanket for insulation, coated with a refractory coating to seal the blanket fibers and protect them from the flame. The weak spot is the floor. Steel slides across it, scale falls on it, and flux (the borax used for forge welding) drips onto it. A dense fire brick or split on the floor gives you a tough, cheap surface that's easy to replace.
You'll also see small "two-brick forges" built from soft insulating fire brick and a propane torch. They heat up fast for small work, but soft brick wears quickly and flux eats right through it.
Forge tips
- Flux eats fire brick. Borax melts into the brick like glass and slowly dissolves it. Use a sacrificial fire brick or split on the floor, and swap it out when it gets glazed and pitted.
- Medium duty handles most hobby forging. If you forge-weld at full heat every day, consider a higher-grade brick for the hottest spot.
- Need a custom shape? Castable refractory cement can be packed into a mold to make a fire pot, burner block, or a lining for a forge body.
- Wear a respirator when cutting brick or handling ceramic fiber blanket, and coat the blanket so loose fibers aren't blown around.
- Ventilate. Propane and coal forges make carbon monoxide. Forge outdoors or in a well-ventilated shop.
Fire Brick for Fireplaces, Wood Stoves, Kilns and Smokers
Not building a pizza oven, fire pit or forge? Fire brick has plenty of other jobs. Here's what to know for each.
Indoor fireplaces
The firebox of a masonry fireplace is lined with fire brick, and most U.S. building codes require it. Full-size brick and splits are both common. Indoors, a premixed air-setting refractory mortar such as Alsey Smithfield Airset or our Super Duty Refractory Mortar makes thin, neat joints. Always follow your local building code for an indoor fireplace.
Wood stoves and fireplace inserts
Many wood stoves are lined with replaceable fire brick, most often 1¼-inch splits. When you replace them, match the size and thickness your stove maker calls for. Don't swap in thicker brick because it seems sturdier; it can crowd the firebox and change how the stove burns.
Pottery kilns
Kilns use both kinds of fire brick. Electric kilns are built mostly from soft insulating brick, which heats up fast and saves energy. Gas and wood-fired kilns use hard brick for floors, fireboxes and any surface the flame hits, with insulating brick behind it. Most pottery kilns are built with high duty or super duty brick, because they hold stoneware temperatures for hours. Medium duty brick can work for lower-temperature kilns, fireboxes and kiln bases.
Smokers, barbecue pits and outdoor kitchens
Fire brick makes a long-lasting lining for the firebox of a brick smoker or barbecue pit. Some pitmasters also set a few loose fire bricks inside a steel smoker to store heat and smooth out temperature swings. In an outdoor kitchen, a fire brick hearth gives you a heat-proof landing spot for hot pans, Dutch ovens and pizza peels.
Boilers, furnaces and industry
Fire brick lines boilers, incinerators, glass furnaces, cement kilns and steel mills. Those jobs often call for specialty high-alumina or other industrial refractories chosen by an engineer. If you're buying for industrial equipment, get the exact grade from the equipment maker.
Is Fire Brick Safe to Cook On?
Yes. New, clean, dense fire brick has been used as a cooking surface in pizza ovens and bread ovens around the world for generations. It's made from natural clay minerals (mostly alumina and silica) that are fired until they fuse into a stable, stone-like block. There are no coatings or additives meant to burn off, and fire brick used within its temperature rating doesn't give off harmful fumes.
To keep your cooking surface safe, stick to a few simple rules:
Do
- Use new fire brick made for ovens and high heat
- Keep the cooking floor clean, bare brick
- Cure a new oven with small fires before cooking
- Let the fire burn off food spills
Don't
- Cook on used industrial brick pulled from a furnace, boiler or kiln. You don't know what chemicals or metals it absorbed.
- Paint, seal, stain or glaze fire brick that touches food
- Use bricks you can't identify, or "fire brick" with no grade or temperature rating
- Clean the cooking floor with soap or chemical cleaners
Part 4 • Building With Fire Brick
Fire Brick Mortar: What to Use, Plus Our Homemade High-Heat Mortar Recipe
Fire brick is only half the job. The mortar between the bricks has to handle the same heat, and for anything built outdoors, it has to survive rain and snow too. Regular bagged mortar from the hardware store isn't made for the heat of a pizza oven or fire pit.
The one rule for outdoor mortar: non-water-soluble
Some high-heat mortars, especially the wet, premixed kinds sold in tubs, are water-soluble. They set up hard as they air-dry, but if they get soaked, they can soften and wash out of the joints. That's fine inside a house. It's a problem on an outdoor pizza oven, fire pit or fireplace. For anything outdoors, use only non-water-soluble mortar. You have two good choices.
Choice 1: BrickWood Refractory Mortar (easiest)
BrickWood Refractory Mortar is a 50-lb dry mix that's non-water-soluble once it cures. Just add water and mix. It costs a little more than mixing your own, but there's nothing to measure and every batch comes out the same.
Choice 2 • The BrickWood homemade high-temp mortar recipe
Homemade High-Heat Mortar: The Recipe Pizza Oven Builders Use Around the World
This is the classic do-it-yourself high-temperature mortar that oven builders all over the world have used for generations, and it's the recipe we recommend for every BrickWood oven. We've recommended it to BrickWood builders for years, and we have never had a single customer tell us it failed. It's simple, it's inexpensive, and it's perfect for pizza ovens, fire pits and outdoor fireplaces.
3 partsFine silica sandThe body and strength of the mortar
1 partHydrated limeMakes it creamy, sticky and a little flexible
1 partFire clayAdds heat resistance
1 partPortland cementMakes it hard and weatherproof
Why this recipe is perfect for pizza ovens
Each of the four ingredients has a job, and together they cover everything an outdoor oven needs:
- Portland cement sets the mortar rock-hard and makes it non-water-soluble, so rain and snow can't wash it out of the joints.
- Fire clay is the same heat-loving clay fire brick is made from. It helps the mortar stand up to oven heat and to the heating and cooling of every fire.
- Hydrated lime makes the mix smooth and sticky so it grabs the brick, and it keeps the cured mortar slightly flexible as the oven expands and contracts.
- Fine silica sand gives the mortar its body and strength, and the fine grains let you make the thin, tight joints a fire brick oven needs.
That combination gives you a mortar that's strong, heat-tough, weatherproof and easy to work with, at a fraction of the cost of premixed refractory mortar.
Ingredient tips
- Sand: use fine silica sand only. Pool filter sand is fine. Don't use play sand, mason sand or concrete sand; coarse sand makes a weak, gritty mortar.
- Lime: use white, powdered hydrated masonry lime (Type S). Don't use agricultural or garden lime.
- Portland cement: use plain Portland cement, not a premixed mortar or concrete mix that already contains sand or lime.
- Fire clay: use powdered fire clay, sold in bags at masonry supply stores and here at BrickWood.
How to mix it
- Measure by volume with the same bucket or scoop for every ingredient: 3 scoops sand, 1 lime, 1 fire clay, 1 Portland cement.
- Mix the dry ingredients together thoroughly until the color is even.
- Add clean water a little at a time and mix until it's thick and creamy, like peanut butter. It should hold its shape on a trowel.
- Mix only what you can use in about an hour.
- Never re-mix mortar that has started to set, and never reuse mortar that has fallen on the ground. Always mix a fresh batch.
Where to buy the ingredients: we sell all four, silica sand, hydrated lime, fire clay and Portland cement, and ship them to your door. You can also find them locally. Portland cement and fine sand are usually at big-box hardware stores, while fire clay and hydrated lime are easiest to find at landscape and masonry supply stores.
Indoor-only mortars
Wet, premixed air-setting mortars like Alsey Smithfield Airset and our Super Duty Refractory Mortar are excellent for indoor fireplaces, wood stoves and kilns, where they stay dry. Because they're water-soluble, they're not for outdoor pizza ovens or fire pits. If a bag or tub doesn't clearly say "non-water-soluble," contact the manufacturer directly to confirm before you use it outdoors. Don't rely on a store clerk.
Mortar vs. castable refractory
Mortar glues bricks together in thin joints. Castable refractory cement is different: it's mixed and packed into a form to make solid shapes, like an oven shell, a forge lining or a custom fire pit insert. Don't use castable as mortar, or mortar as castable.
How to Cut Fire Brick
Dense fire brick is much harder than regular brick, so it takes the right tool. The good news: most pizza oven and fire pit builds only need a handful of cuts, and BrickWood plans show you exactly where they go.
The best tool: a wet tile saw with a diamond blade
A wet tile saw (or wet masonry saw) with a diamond masonry blade gives clean, straight cuts and keeps dust down. You can rent one from most tool rental shops if you don't own one.
- Plan and mark your cuts with a pencil or marker before you turn on the saw.
- Soak the bricks briefly before cutting. Wet brick makes less dust, and a damp brick won't suck the water out of your mortar when you lay it.
- Feed the brick slowly and let the blade do the work. Support both sides so the last bit doesn't snap off.
- Allow for the blade. A blade removes about ⅛ inch, so measure each piece from the correct side of your line.
- Rinse the slurry off the brick and keep it off your cooking floor.
Other options: an angle grinder with a diamond blade works for a few cuts but makes a lot of dust. A brick chisel and hammer can make rough breaks for hidden spots, but not clean, visible edges. Soft insulating brick is different. It cuts easily with an old hand saw.
Cutting safety: protect your lungs
- Cutting fire brick makes fine silica dust, which is harmful to breathe. Always wear a properly fitted N95 or better respirator, plus safety glasses and hearing protection.
- Cut outdoors, and use water to keep dust down. If there's a breeze or you run a fan, keep it at your back so dust blows away from you.
- Keep kids, pets and food prep away from the cutting area.
- Clean up with water or a shop vacuum with a fine filter, never by sweeping dry dust or blowing it with compressed air.
Where to Buy Fire Brick (and What to Ask Before You Do)
Buying fire brick from BrickWood Ovens
BrickWood full-size fire brick is dense, medium duty fire brick rated to 2,700°F and made in the United States. It's the same brick our full oven kits are built around, so if you're building a BrickWood oven, you know it fits the plans.
- Sold by the brick, 160 minimum. 160 full-size fire bricks is enough for a Mattone Barile oven and base. Need more for a hearth, fire pit or spares? Order any quantity above 160.
- FREE shipping anywhere in the U.S. by commercial freight, to a job site, a business or a freight terminal for pickup
- Freight forwarding to Alaska, Hawaii and the Caribbean
- Building a 28-inch Mattone Cupola? It needs fewer than 160 fire bricks. Contact us and we'll ship the exact number your oven needs.
- Building a Cortile Barile? Its cooking floor takes only a small number of fire bricks, so pick them up locally when you buy your other supplies. Our masonry supply store finder can help.
- Still choosing an oven? See all BrickWood pizza oven kits.
Please note: refractory brick is non-refundable and non-returnable.
Buying fire brick locally
- Refractory supply stores sell to kiln, boiler and furnace contractors, and they know their grades. Find a refractory supply store near you.
- Landscape and masonry supply stores often carry fire brick, fire clay and hydrated lime. Find a masonry supply store near you.
- Big-box home improvement stores like Home Depot and Lowe's carry fire brick at some locations. Stock varies a lot from store to store, so call first and ask for the Pro Desk, where staff usually know masonry. If your store is out, ask whether another nearby store has a pallet and can transfer it.
Watch out at big-box stores
- Make sure it's actually fire brick. A new employee may point you to regular clay brick or pavers. If it's red and labeled "clay brick," it's not what you want.
- Check the thickness. Many stores mainly stock 1¼-inch splits made for wood stoves. A pizza oven floor needs full 2½-inch brick.
- Look for a grade and temperature rating. If the label doesn't list one and nobody can tell you, keep shopping.
Questions to ask any fire brick seller
- Is this dense (hard) fire brick, not insulating brick?
- What are the exact dimensions? I need 9 x 4½ x 2½ inches.
- What duty grade is it, and what's the temperature rating?
- Is it new and uncoated?
- How much does one brick weigh, and how many come on a pallet?
- How will it be delivered, and do I need a liftgate or residential delivery?
- What's the return policy if bricks arrive broken?
- Save the label and receipt so you can buy matching bricks later.
Does fire brick color matter?
No. About 98% of the fire brick made in the U.S. is tan or buff, which is just the natural color of the clay. You'll also see red (sometimes sold as "salmon"), ivory or dark brick. Color has nothing to do with temperature rating, strength or quality, and every fire brick turns dark from smoke and soot after a few fires anyway. Judge a brick by its grade and rating, not its color.
Can you reuse old fire brick?
For a fire pit or the outside of a structure, clean old fire brick from a known source can be fine. For a cooking surface, buy new. Used brick from a furnace, boiler or industrial kiln may have absorbed chemicals or metals, and brick usually comes out of a furnace because the lining was failing. Old brick also tends to be chipped, worn and a slightly different size, which makes a bumpy cooking floor.
Part 5 • Making It Last
Curing, Weather, Cracks and Cleaning: How to Make Fire Brick Last
When it's installed and used correctly, dense fire brick lasts for decades in pizza ovens, fireplaces, fire pits and kilns. These habits make the biggest difference.
Cure it before you fire it hot
Fire brick comes out of the factory kiln bone-dry, but it doesn't stay that way. It soaks up water from rain, wet cutting and fresh mortar while you build. If you build a roaring fire right away, that trapped water turns to steam and can crack bricks and joints. The fix is curing: a series of small fires over several days that slowly dries everything out. Follow the curing schedule in your BrickWood instructions, and see our step-by-step guide on how to cure a pizza oven.
Keep it dry
Fire brick is not waterproof. Even dense brick soaks up water like a stone does. Protect a pizza oven with its finished outer shell and chimney cap, cover a fire pit when it's not in use, and if your oven ever gets soaked, dry it out with small fires again before cooking hot. In cold climates, keep the oven covered and dry through winter, and warm it with small fires after a freeze.
Never hit hot brick with water
Don't put out a fire with a hose or splash water on a hot oven floor. The sudden temperature change is exactly the thermal shock that cracks brick. Let the fire burn down and the oven cool on its own.
Are cracks normal?
Small hairline cracks are normal in any high-heat masonry. They come from the bricks expanding and shrinking with every fire, and they usually don't affect performance or safety. A brick only needs replacing if it breaks all the way through or pieces start coming loose. In many oven designs, even a whole cooking floor can be replaced through the oven opening without taking the oven apart, which is one more reason to keep those 10 spare bricks.
How to clean fire brick
- Let the fire do the work. Cheese, sauce and grease that land on a hot oven floor burn away to ash.
- Brush out the ash with an oven brush once the floor has cooled enough to work around.
- Expect it to darken. Fire brick turns dark from smoke and seasoning. That's normal, and many owners love the look. A hot fire will often burn the inside of the dome clean again.
- Skip the chemicals. Don't use soap, cleaners, paint or sealers on fire brick, especially on a cooking surface.
How Fire Brick Is Made
Making fire brick is a lot like making regular brick, but with purer clay, more pressure and far more heat:
- Mix. Fireclay, grog (crushed, already-fired clay) and sometimes other heat-resistant minerals are ground and blended to an exact recipe, then mixed with a little water.
- Press. The damp mix is pressed into molds under very high pressure, often around 8,000 psi, to form the 9 x 4½ x 2½-inch shape. Pressing packs the particles tightly, which makes a denser, stronger brick.
- Dry. The bricks air-dry for about 2 to 3 days so the water leaves slowly. Rushing this step cracks them.
- Fire. The bricks ride kiln cars through a long tunnel kiln for about 48 hours at well over 2,000°F. The clay particles fuse together without melting, a process called sintering, which turns the soft clay into a hard, stone-like ceramic.
- Cool and inspect. The bricks cool slowly, then get checked for size, density and strength.
- Ship. Finished bricks are stacked and wrapped on pallets, 456 to a pallet for BrickWood fire brick.
A short history of fire brick
People have been lining fires with special clay for thousands of years. Ancient potters, glassmakers and metalworkers learned by trial and error that some clays held up to heat far better than others. Manufactured fire brick as we know it took off during the Industrial Revolution, when iron and steel furnaces needed linings that could take nonstop heat. In 1822, William Weston Young founded the Dinas Fire Brick Company in Wales to make a heat-resistant silica brick, one of the best-known early milestones. Over the next two centuries, refractory makers developed the grades, shapes and testing standards used today. The same basic material that lines a steel furnace now lines your backyard pizza oven.
Fire Brick Mistakes to Avoid
Avoid these and you'll avoid most fire brick problems
- Using regular brick, pavers or concrete block where they face the fire.
- Buying soft insulating brick for a cooking floor or fire pit.
- Using 1¼-inch splits where your plans call for full 2½-inch brick.
- Mixing brands or sizes on a cooking floor and ending up with lips that catch the peel.
- Using water-soluble or regular mortar outdoors. Use non-water-soluble high-heat mortar.
- Using the wrong sand or lime in homemade mortar. Fine silica sand and hydrated lime only.
- Skipping insulation and expecting fire brick alone to hold the heat.
- Lighting a big fire in a new oven before curing it.
- Cutting brick without a respirator.
- Cooking on reclaimed industrial brick or painted, sealed brick.
- Forgetting delivery logistics. 160 fire bricks weigh about 1,225 lb.
- Not keeping spares. Set aside 10 matching bricks for future repairs.
Fire Brick FAQ
What is the difference between fire brick and regular brick?
Fire brick is made from fireclay, a heat-resistant clay rich in alumina and silica, and it's fired to survive being heated and cooled over and over. Regular clay brick is made for walls and patios. In a fire it cracks and flakes apart (spalls) over time, and it can shed pieces into food in a pizza oven.
Can I use regular brick in a pizza oven or fire pit?
Not where it touches the fire. Regular brick, concrete pavers and concrete block crack and flake under repeated heating, and pavers and block can pop apart from trapped moisture. They're fine for the base or the outside of the structure, as long as fire brick faces the flames.
What grade of fire brick do I need for a pizza oven?
Medium duty dense fire brick, rated to about 2,700°F. A pizza oven floor reaches about 1,200 to 1,400°F under the flames, so medium duty gives plenty of margin. Higher grades cost more and won't make better pizza.
How hot can fire brick get?
It depends on the grade. Low duty fire brick is rated to about 1,750°F, medium duty to about 2,700°F, high duty to about 2,850°F, super duty to about 2,900°F, and high-fired super duty to 3,000 to 3,150°F. BrickWood fire brick is medium duty, rated to 2,700°F.
What size is a standard fire brick?
The standard U.S. full-size fire brick, called a straight, is 9 x 4½ x 2½ inches. Thinner 1¼-inch versions are called splits and are mostly used as liners for wood stoves and fireplaces.
How much does a fire brick weigh?
A BrickWood full-size fire brick weighs about 7.65 pounds. Most dense full-size fire brick weighs 7 to 8 pounds, a split weighs about half that, and a soft insulating fire brick weighs only about 2 to 3.5 pounds. Our 160-brick minimum order weighs about 1,225 pounds.
What is the minimum order for BrickWood fire brick?
BrickWood fire brick is sold by the brick with a 160-brick minimum, which is enough for a Mattone Barile oven and base. You can order any quantity above 160, and shipping is free anywhere in the U.S. If you're building a 28-inch Mattone Cupola, which needs fewer fire bricks, contact us and we'll ship the exact number your oven needs. If you're building a Cortile Barile, its cooking floor takes only a small number of fire bricks, so most builders pick them up at a local masonry supply store. Fire brick splits are sold the same way, with a 325-split minimum.
How many fire bricks do I need?
For a BrickWood oven, use the materials list in the free plans. For other projects, figure about 3.6 bricks per square foot laid flat or 6.4 per square foot on edge, add about 10% for cuts, and keep 10 spares for future repairs.
Is fire brick safe to cook on?
Yes. New, clean, dense fire brick is used as a cooking surface in pizza and bread ovens around the world. It's made from natural fired clay minerals with no coatings meant to burn off. Don't cook on reclaimed industrial brick or on brick that has been painted, sealed or glazed.
What mortar should I use with fire brick?
Outdoors, use only non-water-soluble high-heat mortar: BrickWood Refractory Mortar (dry mix) or the homemade recipe of 3 parts fine silica sand, 1 part hydrated lime, 1 part fire clay and 1 part Portland cement. Wet, premixed air-setting mortars are water-soluble and are best kept to indoor fireplaces, stoves and kilns.
Is the homemade 3-1-1-1 mortar recipe good enough for a pizza oven?
Yes. It's the classic high-heat mortar oven builders around the world have used for generations, and it's the recipe BrickWood recommends. The Portland cement makes it hard and weatherproof, the fire clay adds heat resistance, the lime makes it workable and slightly flexible, and the fine sand gives it strength. We have never had a customer tell us it failed.
What's the difference between hard and soft fire brick?
Hard (dense) fire brick is heavy, stores heat and has a tough surface, so it's used for pizza oven floors and walls, fire pits and forge floors. Soft (insulating) fire brick is lightweight and full of air pockets, so it blocks heat instead of storing it. It's used for electric kilns and backup insulation, not cooking surfaces.
Can I use fire brick in a forge?
Yes. Dense fire brick is a great floor and fire-area lining for coal, charcoal and propane forges. Forge-welding flux (borax) slowly eats fire brick, so use a sacrificial brick or split on the forge floor and replace it when it gets glazed and pitted.
Do I need fire brick in a fire pit?
If your fire pit is built from concrete block, pavers or stone, a fire brick liner is the best way to keep the outer wall from cracking. Lay the liner with non-water-soluble high-heat mortar, and leave a weep gap so rainwater can drain.
Are fireplace bricks the same as fire bricks?
Yes. "Fireplace bricks" almost always means fire brick, the heat-proof brick that lines a fireplace firebox. Use dense fire brick, full size or splits, wherever the fire touches. Regular clay brick is fine for the face and surround.
What are heat bricks for a wood stove or wood heater?
Heat bricks, also called stove bricks, are fire brick splits that line the firebox of a wood stove or heater. Most are 9 x 4½ x 1¼ inches. They protect the steel and hold heat, so match the size your stove maker calls for.
Are furnace bricks and fireproof bricks the same as fire brick?
Yes, both are other names for fire brick (refractory brick). Industrial furnaces often need high duty or high-alumina brick, so check the rating your equipment calls for.
Is the fire brick at Home Depot the same?
Some home improvement stores carry real fire brick, but stock varies by location and many stores mainly carry thin 1¼-inch splits made for wood stoves. Call the Pro Desk first, confirm it's dense fire brick and not regular clay brick, and check the size and temperature rating.
Does fire brick need to be sealed or painted?
No. Never paint or seal fire brick, especially on a cooking surface. Coatings can trap moisture, interfere with how the brick heats, and give off fumes. Fire brick naturally darkens from smoke, and that's normal.
Is fire brick waterproof?
No. Fire brick absorbs water like stone does. Protect your oven or fire pit from rain, and if it gets soaked, dry it out with small fires before you build a big one.
Do fire bricks crack over time?
Small hairline cracks are normal in high-heat masonry and usually don't affect performance. Replace a brick only if it breaks all the way through or pieces come loose. Dense fire brick that's installed, cured and used properly can last for decades.
Can you ship fire brick to Alaska, Hawaii or the Caribbean?
Yes. BrickWood ships fire brick nationwide by commercial freight and can coordinate freight forwarding to Alaska, Hawaii and the Caribbean, with job site, business or freight terminal delivery.
Shop BrickWood Refractory Materials
Everything you need to build with fire brick, shipped to your door. Browse the full refractory materials collection, or jump straight to a product below.
Pizza Oven KitsDIY brick oven kits with FREE plansShop now →
Fire Brick Splits9 x 4½ x 1¼ in, for liners and tight spaces. 325 minimum.Shop now →
Refractory Mortar50 lb dry mix, non-water-soluble, for outdoor buildsShop now →
Fire ClayHomemade high-heat mortar ingredientShop now →
Hydrated LimeHomemade high-heat mortar ingredientShop now →
Silica SandHomemade high-heat mortar ingredientShop now →
Portland CementHomemade high-heat mortar ingredientShop now →
Castable Refractory Cement55 lb dry mix for casting shapes and liningsShop now →
Ceramic Fiber Blanket, 6 lb1 in x 24 in x 25 ft, pizza oven insulationShop now →
Ceramic Fiber Blanket, 8 lb1 in x 24 in x 25 ft, denser blanket for ovens and forgesShop now →
Vermiculite / Perlite4 cubic feet, for insulating concreteShop now →
All Refractory MaterialsMortars, castables, insulation and moreShop now →Build It Once. Build It With Real Fire Brick.
The difference between a pizza oven, fire pit or forge that lasts a season and one that lasts decades comes down to a few choices: dense fire brick where the fire is, non-water-soluble high-heat mortar to hold it together, insulation to keep the heat in, and a gentle cure before the first big fire.
Medium duty. Full size. Made in the USA. Rated to 2,700°F. FREE shipping.
Building a pizza oven? Explore BrickWood pizza oven kits, keep your installation instructions handy, and bring your questions to the BrickWood builder forum.
Keep Reading
This guide is general information. Always follow the plans and instructions for your project, the directions on every product you use, and your local building codes, fire codes and burn rules. Wear eye, ear and respiratory protection when cutting masonry.
