Hi, you can probably tell by the question, but I've just started looking into this type of thing. I was harvesting clay to make my own bricks for a fire pit (potentially a forge), but I found out that normal bricks wouldn't work very well in a high temperature forge. I saw a few videos about people making simple forges, some of which used clay, but they all seemed to disagree on how effective clay is, and what you can add to it to improve its qualities. 

I've been looking into high temperature bricks and mortar, but I don't want to have wasted all the time I spent filtering out impurities from my clay. Is there any way I can use it in a high temperature forge?

Welcome to the show. If you would fill out your header to give us an idea where you are in this great big world. Just general location nothing specific. You may be living right around the corner from me or many others who could give real time advice. Also many things, such as price of tooling, is location dependent. What i may call a cheap anvil others may call way overpriced for example. 

Next go towards the bottom of the main page to the introduce yourself thread and, well, introduce yourself. Let us know a bit about you. Your interests, hobbies, etc. 

To answer your question. Yes clay can be useful for lining your forge. Mix it with a little sand and it will work out much better than clay alone. Someone should come along and give you the ratio of clay to sand. I can not remember at the moment. Plain old clay will crack. Most forges are iron or steel, the clay is used to create a barrier between the heat and the metal. This barrier will keep the metal from oxidizing, rusting, away. 

High temp bricks, or fire bricks, the hard ones can be used to also line the forge or table but do not use in a gasser. You want the soft ones for that.  And if you are talking about the mortar you find at the local hardware store for stoves it will not hold up to the heat from the forge, that stuff is made for stoves that do not get as high temp as a forge. 

A trick many use for clay is cat litter, not the clumping stuff, or floor dry. Both are ground up bentonite clay and when mixed with water become malleable again.  

Welcome aboard, glad to have you. 

What kind of forge do you wish to build? 

If you want a solid fuel forge, coal or charcoal, you don't need more than garden soil let alone brick.

If you wish to build a propane forge then home made fire brick only turn into grog. It requires pretty high tech manufacturing processes to make a light firebrick that will survive the rapid thermal cycling of a propane forge. A 3,000f hard firebrick is intended for reasonably gradual heat up a propane burner tends to have the spot the flame hits turning red before the area around it. Being hard and brittle differential heating tends to cause them to break up. The hot spots expands faster than the rest and there isn't ANY room to flex in hard brick.

Don't sweat it, I STILL have a 15gal grease barrel holding 2 sacks of hire clay in the shop, it's been there since before we moved here. I tried making my own fire brick, light insulating and other wise before one of the guys at the local furnace supply told me about 9lb. Kaowool insulating refractory blanket. Turned me onto all the trimmings in their dumpster.

I use some of the case of hard firebrick when I'm using my rivet forge but on edge around the air grate to shape and control the fire. Not as the floor or "firepot." 

Frosty The Lucky.

Welcome from the Ozark mountains

If you are wanting to build a permanent brick solid fuel forge (coal/charcoal) and make your own bricks, they should be made as adobe bricks. Clay, Sand and Straw. However you will still need a steel or cast iron forge table and fire pot.

BP0553 Building a Brick Forge - 100 Series - I Forge Iron

I suggest starting out with a JABOD (Just A Box of Dirt) to see if you really want to use a solid fuel. They are portable and easy to move around. Might look through this for ideas.

https://www.iforgeiron.com/forum/267-jabod-just-a-box-of-dirt/

 

I can’t control the wind. All I can do is adjust my sails. ~Semper Paratus~

 

Funny enough, I made my JABOD and thought I would go an extra step and line it with clay. I dug up some plain old dirt that was a little damp already and tamped that in. The clay came from the pig waller. That might be disturbing to some lol. I mixed in a bit of wood ash and went to work. Let it dry for a day and a half. It's hot here so I thought that might do the trick. It cracked. I think I may have used too much water or not enough whatever else it needed. Anyway, even though it cracked in some places, it's held up well through a few fires except in the firepot. I haven't bothered to reline it though as I don't think it needs it. Just reshaping with damp dirt 

And THAT is the basic idea of a JABOD forge. Size, shape, depth, whatever you need or want at the time and when you're finished and it's cool forget it. If you're traveling take the box but leave the dirt home, it's everywhere. 

The only real trick is getting it packed hard enough you don't stir it up putting the stock in and out and tending the fire. You don't want dirt mixed with the coals.

The above is a perfect example of "dirt". The definition being, dirt is misplaced soil. The stuff in your yard with grass growing out of it or the garden, flower pot on the window ledge, etc. contain "Soil". Spill it on the carpet, grind it into your knees etc, and it's "Dirt."

Believe it or not it is one of the first things in the ASHTO soils manuals. You'd have to work in a soils lab to understand how confusing it can be for non-labrats. Bill, "DANG I dropped the sample pan, I gotta go brush the dirt off me before I recover the soil from the countertop and floor." The lab foreman, "Get it all, don't contaminate the sample with dirt!"

The materials lab was kept meticulously clean, spills were cleaned up immediately or as soon as it was safe. It's surprising how easy it is to render a gradation worthless with half a gram of dust off a cabinet top. That specifically was a demonstration for all labrats in training.

On a final note, a JABOD should be JABOS. The soil mix packed in your JABOD is SUPPOSED to be there and by definition it's not misplaced. It's Soil, not dirt.

Frosty The Lucky.

 

JABOS... doesn't quite have the same ring, but you are absolutely right. Soil, not dirt. You have such a way of making me see things so much differently 

Ah, it doesn't really matter, that was just the old labrat coming out. I usually just go along with the common terms rather than explain. It's the real world, not a laboratory after all.

Dad probably primed me for terminology as a youngster. He was a rock hound and was all about the proper name and description of various rocks. Calling them rocks and rock hounds was an in joke among the collectors. Most clubs are now "gem and mineral societies", not enough pretension in rock club. 

I seemed to be on a roll yesterday, I think I wrote a couple pages about dog behavior and training. I hope I didn't get too carried away. <sigh> 

Frosty The Lucky.

I've made several just a box of dirt (JABOD) or similar forges, including the one in my avatar photo, which sort of a jabod/rotor forge hybrid, and I also like to harvest and play with clay. You can, and I have used harvested clay, but that's a lot of work, and just like pottery work, you have to temper it with at least 10 or 15 percent sand or it wants to crack. Unlike pottery, it doesn't need to be a particularly fine sand. However, I would strongly consider using plain ordinary dirt in a JABOD as suggested above, unless your soil is inappropriate for some reason. It's about the easiest build you can do and works well with most types of solid fuel.

Clay is better suited for lining a regular forge with a tuyere, and even then, as above, temper it with some sand, and remember that it tends to trap water. It works lovely with coal for a "duck's nest" style forge built over a rotor (not a drum). Forging with charcoal, I've had better luck with a trench and a side blast. I do like using removable clay walls at the top of the trench when I want to pile fuel up higher.

There's another style I've seen that I like too but haven't used myself - they build a clay hearth with a wall to one side of the fuel, and then blow air from the side, through a tuyere set in the wall. With charcoal, you'll still need a way to pile the fuel up though.

Are you describing a fire back forge? Does the blast aimed through the back, parallel or at it?

Frosty The Lucky.

The one I'm describing with the hearth? Possibly. The wall looks like a fireback, except they're usually made of clay, or at least coated in it. The tuyere is perpin..perpendi...at right angles to the wall. Yeesh, I shouldn't drink and post four-bit words.

I have no idea what it's called and currently am looking through videos of overseas forges to find an example - I haven't seen them much in the US although I know I have a book buried somewhere with a very good description of it and I've seen people forge on them.

The typical version is a clay hearth about four inches thick sometimes with a slight dip in which charcoal is piled. To one side, there is a clay wall, typically about a foot to a foot and a half in height and about three inches thick, often describing a parabola, or at least arced at the top, and the tuyere pokes through the wall at a 90-degree angle acting as a side blast, and sometimes providing support to the fuel. The wall protects the bellows/tuyere and may act as partial support for the fuel.

Think of the clay taco you see in some of the Viking or Anglo-Saxon forges if the taco was bigger and one of the walls was laid down sideways.... Sometimes, they leave off the hearth and the bottom is just on dirt. I'm certain I saw a video a couple of years back where a couple of guys were forging knives using one and also using a half-buried howitzer shell with the explosives removed for an anvil.

Okay, I'm well into my second scotch and water so we're at least close to the same page.

Is this close to what you're describing. Picture a piece of paper folded at a 90 degree angle, one side pointed upwards, call it the fire back. In about the center of the bottom, call it hearth, at the fire back is the depression, not too deep, an inch or so. Just above the intersection centered on the depression is the tuyere pipe, aimed slightly downwards. You pile fuel against the fireback and rake it into the fire at the tuyere. 

Different sizes and details, especially the table / hearth but it's very like a side blast trench forge in operation and effectiveness but a lot roomier.

I remember the howitzer anvil, it was the projectile I believe, a 155 maybe? I remember those videos.

Frosty The Lucky.

Perpendicular. 

Scotch and water, sounds good. I think any kind of whiskey and water is kind of an old timey drink. I used to drink bourbon and water and would get weird looks when i would order one. If i am wanting a taste of whiskey now i get a Bushmills over crushed ice. My son in law got me a Tyrconnell 10 year old single malt that was finished in a madeira cask a few years back that i have about enough for 2 drinks left of... 

The word "whiskey" comes from the Gaelic "uisce beatha" meaning "water of life". 

That forge you are describing sounds like the ones that i see at Colonial period reenactments. Usually in the back of a wagon with a bellows above it. I tried looking for a pic of them but to no avail. 

Irish Whiskey, IRISH!?!!?  Blasphemer! May your own shillelagh drub you soundly!

Truth is the main difference between Scotch and Irish is how the malted barley is dried and I find peat smoke suits my palate better though I've enjoyed some Irish whiskey's. 

Here's a real giggle for you, currently my favorite single malt Scotch is Parks Highland and it's the cheapest single malt highland Scotch around. 

The Gaelic pronunciation of "uisce beatha" is amazingly close to Whiskey which is a phonetic spelling in English.

I'm not much of a drinker, in fact  haven't even had a buzz in years but I do love my a Scotch and water toddy of an evening. 

Frosty The Lucky.

I am not much of a drinker, anymore. When i was in the Army though... 

Like i said my SIL bought me that bottle 6 years ago i think. Now if i drink i may have a beer when i come home from work or out on my porch in the evenings on weekends. I do like to make a wine or mead as well and enjoy that sometimes. Had a 1 year old blueberry pomegranate mead the other day that was quite tasty.   

 

I used to put one on when I was younger but after a while I realized it made me sicker than was fun. Now I've lost my taste for beer, I used to really enjoy a dark beer, porters never got drank by any of my friends but they just don't taste good anymore. At one time we used to brew our own and some of those were dynamite strong, 1/2 of a 16oz bottle was enough to give 2 people a nice buzz. 

A neighbor up the creek from our cabin wanted to put up a batch but didn't have enough sugar and the store in town was out so we used honey. They had a couple largish jugs so we put it all in. The hydrometer said it'd be pretty strong but still in the beer range. A can of malt too of course.

We used the bok to start a batch of sourdough which was pretty darned nice. Didn't work so well when we used sourdough to make beer though. Oh it made beer but the flavor was odd. 

We did make a barrel of mead with some of the honey and that turned out pretty well, tasty and a mule kick. Popular stuff while the honey lasted. Why did we folks living miles from the nearest town have a pallet of 5gal cans of honey? They sold for $0.50 a can if you bought the pallet at an auction. I don't remember how many total cans there were but they were stacked 2 deep on a pallet. The folk at the auction bought 2 pallets. EVERYBODY in the little community was cooking with honey for a long time, bread, in your biscuits and pancakes, on your biscuits and pancakes. A neighbor made me a sourdough, honey birthday cake with honey frosting. It was like a kid given free range in a candy store, after a while anything else was a treat.

Good times though.

Frosty The Lucky.

On 8/2/2025 at 11:02 AM, BillyBones said:

Welcome to the show. If you would fill out your header to give us an idea where you are in this great big world. Just general location nothing specific. You may be living right around the corner from me or many others who could give real time advice. Also many things, such as price of tooling, is location dependent. What i may call a cheap anvil others may call way overpriced for example. 

Next go towards the bottom of the main page to the introduce yourself thread and, well, introduce yourself. Let us know a bit about you. Your interests, hobbies, etc. 

To answer your question. Yes clay can be useful for lining your forge. Mix it with a little sand and it will work out much better than clay alone. Someone should come along and give you the ratio of clay to sand. I can not remember at the moment. Plain old clay will crack. Most forges are iron or steel, the clay is used to create a barrier between the heat and the metal. This barrier will keep the metal from oxidizing, rusting, away. 

High temp bricks, or fire bricks, the hard ones can be used to also line the forge or table but do not use in a gasser. You want the soft ones for that.  And if you are talking about the mortar you find at the local hardware store for stoves it will not hold up to the heat from the forge, that stuff is made for stoves that do not get as high temp as a forge. 

A trick many use for clay is cat litter, not the clumping stuff, or floor dry. Both are ground up bentonite clay and when mixed with water become malleable again.  

Sorry about the late reply! I got sick for a few days and ended up forgetting about the post.

I couldn't find the introduction thread, so I'll think of something to write of my profile.

I'm currently making a fire pit, and after some advice, I'm planning to make a smaller pit in the center, connect it to two pipes (one on each side), cover it with either clay or refractory brick, and use it as a solid fuel forge, or maybe just to melt things down for later. Of course, I'll be making something to cover up the inner pit when it's not in use.

Its all good. As you can see we have been talking amongst ourselves. You will find that thread drift can be strange at times. 

 

Don't sweat it Diz, this isn't a chat, some of us only check in occasionally. It's not like we'll dock your pay. 

I had to delete a way too long post describing making charcoal, happily I realized before submitting it! I get pretty wordy. I'll see what IFI threads I can find to give you a head start reading applicable threads here.

https://www.iforgeiron.com/topic/43490-hookway-charcoal-retort/#comment-447981

These should get you started.

Frosty The Lucky.

 

5 hours ago, Frosty said:

Don't sweat it Diz, this isn't a chat, some of us only check in occasionally. It's not like we'll dock your pay. 

I had to delete a way too long post describing making charcoal, happily I realized before submitting it! I get pretty wordy. I'll see what IFI threads I can find to give you a head start reading applicable threads here.

https://www.iforgeiron.com/topic/43490-hookway-charcoal-retort/#comment-447981

These should get you started.

Frosty The Lucky.

 

Oh, not to worry! I've got a pretty good handle on how to make charcoal.

That does remind me though, would charcoal dust work well as an insulator? Maybe aquarium sand? I've heard that's helpful too.

Do you think grinding sand to a powder before mixing it in would help or hinder the clay?

An insulator? You're not thinking of making fire brick are you? A clay forge bed doesn't benefit from insulation. Aluvial sand works better than crushed. What the sand does in a clayed forge pan is to keep it from being HARD like a brick, it allows the liner to shift a little with thermal cycling so it's less likely to heat check. (crack)

A Jabod (Just A Box Of Dirt) forge is easy and inexpensive to make and the garden soil works well. Clay is okay but you really have to add sand or it WILL break up pretty quickly, starting with the first fire.  

I don't recall the ratios but figure 2or3 pts sand to 1 pt clay. and ONLY enough moisture to let you ram it hard, take a wooden mallet to it till it bounces, then scrape it to shape and burnish the fire trench with moist burlap. Smooth is gooder, your fire tools and project stock won't gouge it as easily.

Do NOT make mud or it WILL shrink check (crack) as it dries.  If you can take a small pellet and roll it into a rope between your palms is is WAY TOO WET. If you can squeeze a handfull HARD and it makes a hard lump without leaving your palm moist and breaks cleanly without crumbling it is moist enough.

If you're going camping take your JABOD but leave the dirt home, there's dirt everywhere, mix too dry with some too moist till it passes the squeeze break test and fill your JABOD box. cut your trench to expose the tuyere iron and your forge is ready to go to work.

About this time of year Wally World or similar Big Box should have mattress / raft, etc. inflaters on sail. Look for the ones that are longish cylinders with a handle on one end and a foot rest on the other. These are modern box bellows. Connect the hose from the inflator to the tuyere pipe on your JABOD and you have a side blast trench forge smiths from a couple millennia ago would recognize.

If you're right handed you'd stand at the forge right foot on the bellows and working it with your right hand while you tend the fire with your left. Your tongs, fire rake and poker at your left hand and your forging hammer on the anvil to your left. When the steel is to heat you let go of the bellows, take the work with the tongs in your left hand, turn left and go to work.

If you were to use a ground forge you'd do much or all your work sitting down, maybe with your feet in a hole if you were going to be there long enough. Your bellows could be almost any sack you find or make and a piece of tubing or pipe to the tuyere. 

Charcoal needs a GENTLE blast or it'll burn to ash in a couple minutes while blowing burning embers all over you and scattering gleeties to the trees.

It's about bedtime for me, more later.

Frosty The Lucky.

15 hours ago, Frosty said:

An insulator? You're not thinking of making fire brick are you? A clay forge bed doesn't benefit from insulation. Aluvial sand works better than crushed. What the sand does in a clayed forge pan is to keep it from being HARD like a brick, it allows the liner to shift a little with thermal cycling so it's less likely to heat check. (crack)

A Jabod (Just A Box Of Dirt) forge is easy and inexpensive to make and the garden soil works well. Clay is okay but you really have to add sand or it WILL break up pretty quickly, starting with the first fire.  

I don't recall the ratios but figure 2or3 pts sand to 1 pt clay. and ONLY enough moisture to let you ram it hard, take a wooden mallet to it till it bounces, then scrape it to shape and burnish the fire trench with moist burlap. Smooth is gooder, your fire tools and project stock won't gouge it as easily.

Do NOT make mud or it WILL shrink check (crack) as it dries.  If you can take a small pellet and roll it into a rope between your palms is is WAY TOO WET. If you can squeeze a handfull HARD and it makes a hard lump without leaving your palm moist and breaks cleanly without crumbling it is moist enough.

If you're going camping take your JABOD but leave the dirt home, there's dirt everywhere, mix too dry with some too moist till it passes the squeeze break test and fill your JABOD box. cut your trench to expose the tuyere iron and your forge is ready to go to work.

About this time of year Wally World or similar Big Box should have mattress / raft, etc. inflaters on sail. Look for the ones that are longish cylinders with a handle on one end and a foot rest on the other. These are modern box bellows. Connect the hose from the inflator to the tuyere pipe on your JABOD and you have a side blast trench forge smiths from a couple millennia ago would recognize.

If you're right handed you'd stand at the forge right foot on the bellows and working it with your right hand while you tend the fire with your left. Your tongs, fire rake and poker at your left hand and your forging hammer on the anvil to your left. When the steel is to heat you let go of the bellows, take the work with the tongs in your left hand, turn left and go to work.

If you were to use a ground forge you'd do much or all your work sitting down, maybe with your feet in a hole if you were going to be there long enough. Your bellows could be almost any sack you find or make and a piece of tubing or pipe to the tuyere. 

Charcoal needs a GENTLE blast or it'll burn to ash in a couple minutes while blowing burning embers all over you and scattering gleeties to the trees.

It's about bedtime for me, more later.

Frosty The Lucky.

The main project is a fire pit, not the forge itself. That'll just be a bonus. I'm thinking of putting clay into the bottom of the pit, so it's easier to collect the ash. I could probably use it for firing clay too. That's why I'm looking for ways to insulate the clay.

How do you plan on firing the clay in the bottom of the pit? If you don't, it will dry and scrape up when you clean the ash. AND it WILL absorb moisture from the ground let alone rain and WILL turn to mud. Then it freezes and heaves and . . . <sigh>.

Have you considered making a compacted bed, laying firebrick and filling the spaces with a fire clay sand mix? Rather than filling with dry mix you could buy a tube or two of premixed fireplace mortar instead.

The problem with mortar on a fire pit floor is thermal expansion cycles, the brick WILL expand and contract much faster than the ground below them so I'd expect heat checking, hopefully the cracks would follow the mortar and remain in a joint but I wouldn't put money on it.

The advantage of using a dry mix is it allows the brick to shift without breaking during thermal cycles. You WILL want to leave an inch or so of space around the brick floor so they don't run out of room to expand and buckle the floor.

If you like the idea and decide to do it, let me know. I spent 20 years working for Alaska DOT materials headquarters, foundations as a driller on the bridges and foundations crew, designing foundations that move in predictable ways so bridges, highways, Rail road crossings, etc. stay where they're supposed to. OR foundations that will literally tear apart or rip big gobs of the ground out if something tries to move them. Steel displacement piles are typically 36" - 48" in diameter x 3/4" thick DOM steel driven into the soil to refusal. Refusal is an engineering number that says the pile can't be loaded heavy enough to push farther into the ground without collapsing the pile. A displacement pile literally pushes the soil out of it's way as it's driven and once the impact vibration of the pile driver stops, the soil that has been displaced presses back against the pile with crazy pressure, further stopping a pile from moving. This is called "Skin Friction" and is the only thing that prevents Alaska's seasonal freeze thaw cycle from jacking piles up from target depth. This is a B A D thing.

Sorry, I don't mean to give you a lesson on bridge foundations but I wanted you to know I know of which I speak. 

Frosty The Lucky.

7 hours ago, Frosty said:

How do you plan on firing the clay in the bottom of the pit? If you don't, it will dry and scrape up when you clean the ash. AND it WILL absorb moisture from the ground let alone rain and WILL turn to mud. Then it freezes and heaves and . . . <sigh>.

Have you considered making a compacted bed, laying firebrick and filling the spaces with a fire clay sand mix? Rather than filling with dry mix you could buy a tube or two of premixed fireplace mortar instead.

The problem with mortar on a fire pit floor is thermal expansion cycles, the brick WILL expand and contract much faster than the ground below them so I'd expect heat checking, hopefully the cracks would follow the mortar and remain in a joint but I wouldn't put money on it.

The advantage of using a dry mix is it allows the brick to shift without breaking during thermal cycles. You WILL want to leave an inch or so of space around the brick floor so they don't run out of room to expand and buckle the floor.

If you like the idea and decide to do it, let me know. I spent 20 years working for Alaska DOT materials headquarters, foundations as a driller on the bridges and foundations crew, designing foundations that move in predictable ways so bridges, highways, Rail road crossings, etc. stay where they're supposed to. OR foundations that will literally tear apart or rip big gobs of the ground out if something tries to move them. Steel displacement piles are typically 36" - 48" in diameter x 3/4" thick DOM steel driven into the soil to refusal. Refusal is an engineering number that says the pile can't be loaded heavy enough to push farther into the ground without collapsing the pile. A displacement pile literally pushes the soil out of it's way as it's driven and once the impact vibration of the pile driver stops, the soil that has been displaced presses back against the pile with crazy pressure, further stopping a pile from moving. This is called "Skin Friction" and is the only thing that prevents Alaska's seasonal freeze thaw cycle from jacking piles up from target depth. This is a B A D thing.

Sorry, I don't mean to give you a lesson on bridge foundations but I wanted you to know I know of which I speak. 

Frosty The Lucky.

Ha, the bridge stuff was pretty interesting actually.

What exactly /is/ fireclay? I've seen it mentioned a bunch, but no consensus on what it is. 

I'm planning to add a clay layer to the outer circle, make cuts in the clay to help it expand, make a fire in the inner, cover up the pit, and use the air tubes to slowly increase the heat. 

One that's done, I'll either do the opposite and layer the lower pit with clay and make a fire in the outer, or just make a plate to cover up the center and leave it as dirt. Might be easier.

It's a type of clay, not a specific clay. Wiki has a pretty good explanation and links.

https://en.wikipedia.org/wiki/Fire_clay

I hope your firepit plans work out for you. 

Frosty The Lucky.