To Clay, Or Not To Clay

[GustavDebels949]

I got my coal forge from a neighbor farm that was long sense non operational. I've use it a hand full of times the way it sits, burning only coal. The forge does have the word "CLAY" cast into it, but I have never thought much of it.  

My questions are....

 

-Should I have the forge lined with refractory clay of some type?

-Am I safe to burn coke in this forge without clay?

-Where can I get refractory clay/ how can I make it?

 

Thank you!

[VaughnT]

It is strongly recommended that you clay a cast iron forge like that.  Cast iron is a rather brittle metal and stress on it can cause a crack quicker than you can spit.  If you wet your coal while the forge is running (to contain/shape the fire) you can cause a crack.  If the forge had been bumped around a lot, the stress in the metal can cause a crack.

 

Best bet, give the gal a coat of clay so that the heat of the fire can be absorbed and distributed over a thicker area.  They wouldn't have put "clay" on there if they didn't think it was in your best interest.

 

You can buy refractory/stove cement at the home stores, or you can make your own using kitty litter, sand and ash.  

[Frosty]

While fire clay or other refractory is good, it's not really necessary, plain old clay from the river bank is fine. Just dampen the clay so it forms a lump when squeezed hard without leaving a damp or dirty hand. If it breaks clean it's good, if it crumbles it needs a little more water. Once it's about right, ram it in with a mallet and smooth, then score it with a thin something, butter knife popsicle stick, etc., It's going to shrink check no matter what and the scoring puts the cracks where you want them. You can burnish it with burlap though isn't necessary but helps keep clinker, etc. from sticking. If you get the clay too wet it will shrink check as it dries like a pond bottom you just want enough moisture to compact.

 

Anyway, if the forge pan says clay or clay before using. CLAY IT.

 

Frosty The Lucky.

[Farmall]

 So, if it doesn't say "Clay", then there is no need?  I have read all the posts about claying a forge that I could find on Iforgeiron, and it seems that, if it is cast iron, the consensus is to clay.    I have always wondered about this as the many opinions voiced herein don't provide much of clue.  I know people that have used CI forges for years with no issues, and those that have used them once or twice and they cracked.  With all that said, can we say with absolute clarity, that, as long as the forge is Cast Iron, that there should be a lining put in it (whether or not it says "clay")?

[VaughnT]

Farmall, absolutely yes.  If the pan is cast iron, it needs to be clayed even if it has a separate fire pot like the one above does.  

 

Cast iron doesn't respond well to differential heating so it could crack any time you wet the coal.  You can't go wrong by adding clay, but if you don't...... it's just a matter of time before a crack develops.

[Farmall]

That's what I thought.....just wanted to be sure because I have read too many posts that go on both sides of the fence.  Just because "I have used it for years and no cracks yet" doesn't mean the Cast iron isn't being stressed.  Thank you Stuart and Vaughn for the clarity that the discussion needed.

[GustavDebels949]

Thank you again for your help, here is the next round of questions on the topic...

-Will this clay work for what I'm doing? http://www.menards.com/main/heating-cooling/hvac-cleaners/high-heat-furnace-cement-furnace-and-stove-cement-heavy-body/p-1450165-c-8528.htm
-Where do I apply the clay? All over the pan? Around the firepot? In the firepot?
-How thick do I apply it?

[Nobody Special]

That would work. Fire clay generally goes something like 7 or 8 bucks for a 50 lb bag at a building supply company. Might find it at a masonry place. I dunno. I use homemade refractory in mine, using the recipe from backyardmetalcasting.com (since i started into this from doing casting, portland cement, sand, perlite, and fireclay). Worried that the portland would slag, but I've only had to patch it once, two years ago, when it cracked a chunk off near the pot.

 

Mine's about 2 to 3 inches deep (brake disk in an old lawnmower, so variable height). I like mine throughought the pan so that it's an even space and easy to move the coal around. Not sure about over the pot. I wouldn't have thought so, but the dire tales around cast iron are making me paranoid....if it's a cast iron pot and not steel.  Somebody will surely correct me. :)

[Frosty]

The main question of whether to or not to clay comes down to my basic philosophy. "It's better to have it and not need it than need it and not have it." Deb likes to say, "Can't hurt, might help."

 

The worst bad consequence of using clay is providing a place water can stand against the pan and speed corrosion. Just cover it when not in use and residual heat will dry it nicely, a steel cover like the end of a 55gl. drum is perfect, it not only keeps weather off it it provides a fire proof cover so a residual spark can't get away from you.

 

Gustav: No, that's furnace cement it's intended to cement (think glue) furnace elements together, think mortar on bricks. What you want is plain old clay that isn't going to glue itself to the pan. Over the years the clay will deteriorate, it'll get gouged by steel, tools, etc. AND it WILL heat check so eventually you're going to want to replace it. Cement isn't going to just pop out for you, it'll be a hard fight, sticking permanently is what it does.

 

A bag of fire clay available at most ANY cement company should run in the $25/ 50lb bag and will line a typical forge pan many times. soone has that covered for decades. Mix in some sand, 1pt sand to 3pts fire clay is good. the sand will make it a little more porous so entrained  moisture won't cause spalling (clay bits popping and flying around as it heats.) it'll also help limit heat checking.

 

Make the liner an inch or more, just eyeball it and ram it till the mallet bounces. Make it smooth so tools and steels won't gouge easy, it'll not only look good it'll make it tougher. Remember to slope it down into a dish around the air grate unless your forge has a fire pot. It isn't going to work very well if the air can't get to the fire, right? <wink> this is how I clayed my old pan forge, as a "duck's nest", the dish around the air grate, this makes a nice small fire if you want or you can mound the entire pan and build a HUGE fire. what I use to contain the burn are fire bricks stacked as I need around the air grate. That acts as the fire pot and I really like being able to customize the fire pot.

 

The easiest way to mix clay is in a sealable container, a plastic bucket with a lid is perfect on all counts. You aren't going to need a lot so don't make a lot, you can even go so far as to fill the pan with dry clay to a little deeper than you want, figure 1/2 again as much, it will compact. Put the clay in the bucket and measure out 1/2 as much sand, sharp silica mason sand is perfect. Wet the sand first then do a fast mix in the bucket, put the lid on and roll it around for a while, end over end is good to. Check after a while and see how well it's mixed. don't expect the clay to have absorbed the water evenly, clay needs time to let this happen so seal the bucket and leave it set till the next day or a week, there is NO too long to let clay and sand temper.

 

When it's moist enough you can squeeze a lump in your fist that doesn't leave a wet spot or crumble, you're good to go. If it's too wet add a LITTLE more sand/clay mix and roll it around and let it set. If it's crumble add a LITTLE water, roll and rest it. don't worry about getting the sand/clay tempered perfectly, close is good enough, this isn't green sand casting so just right isn't critical. What you need here is clay that rams up hard without crumbling and isn't sticky wet or it'll shrink check badly. that's all.

 

Fire clay is NOT necessary, all the forge needs is something that will ram up hard and shield it from direct localized heat. Smiths have been using wooden boxes lined with dirt for centuries. the soil is a heat shield, that's all. You may have the perfect soil in your back yard or the old river side or . . . Selecting a natural clay is where the squeeze a lump in your fist comes in. It should form a hard lump and if you're really lucky and the moisture is about right, it'll break cleanly and not crumble or leave a wet muddy smearl

 

I know, this has been a long windy post and a lot isn't really necessary but clay it carefully and it'll last a long time, just ram it up with damp dirt and it'll work just fine for a short time.

 

Frosty The Lucky.

[tomhw]

Clay the pan, if you must.  I prefer Grout mixed with a minimum of water.  Keep clay and cement out of the fire pot, it becomes clinker.  Cast Iron forge parts are consumable.  Replace them as needed.

[GustavDebels949]

So I picked up a bag of plain "fire clay" from the local masonry supply yard. On the bag it has a formula for fire clay mortar, would this mortar be more favorable than Frosty's 3 to 1 clay and sand mixture?
The formula is...
2 parts Portland cement,
6-9 parts mortar sand,
1 part fire clay

[Frosty]

Mortar is for holding bricks together rather than forming a shield against heat. It's your call, let us know how it works.

 

Frosty The Lucky.

[GustavDebels949]

Well Frosty, it's your call actually. I'd be willing to bet that you've been doing this for twice as long as I've been alive, or longer! I am plenty capable of making my own judgements, but I'm going to leave this one to somebody who knows what their doing, and has done this before.

So on that note, you suggest your mix of clay and sand?

I mixed up a coffee cup full of your suggestion right when I got the clay. It came out exactly as you said it should. When it hardened up it seemed kind of chalky and easy to break, is that normal?

[Frosty]

Don't sell yourself short, asking advice and or otherwise collecting information doesn't put the decision making in someone else's lap. You're making and adapting your tools

 

The mix dried chalky and crumbly because it's just dry clay, unless you fire it it'll always be friable and water soluble. It's only purpose in the forge pan is as a heat shield. If you poke and scrape it, it'll gouge and scrape leaving loose dust and grit. Just take it easy on the forge table and it'll last a while.

 

The problem with using mortars is they will glue themselves to the forge pan so when they wear out and you need to replace it you'll be spending a lot of time getting it out. the mortar mixture recommended on the fire clay bag is for laying brick fire places, BBQs, fire pits, etc. not forges. That mix will withstand wood fire temps with minimal chance of the portland cement spalling but running the temp higher and I don't think so. The forge WILL get hotter around the air grate and the heart of the fire.

 

Just so you know, I'm a propane forge guy, I've used charcoal and coal, even have a couple few solid fuel forges around but I'm primarily a propane guy. I did spend a number of years working in the State materials lab where you can ask darned near anything having to do with construction materials and if somebody doesn't know the answer there's a book on the shelf. Believe it or not, I did indeed look up how to mix a refractory from fire clay. It's been WAY long ago I did it but the recipe isn't a formula there's wiggle room so the recipe I posted is close enough to work. Probably NOT in a ceramic kiln but maybe, I'd have to bug one of the guys where I used to work to look it up for me for hard numbers.

 

If you want good hard numbers hit the library and check out a kiln making book or have them do an inter library loan and get you a copy. Humans have been making kilns for thousands of years and they typically take much higher heat than a forge.

 

Frosty The Lucky.

[mike-hr]

I'll throw in.. I have a cast iron Champion forge I take to demo's and hammer-ins. I put refractory cement in it for a couple years, it seemed to peel up and lift off all the time. I leave it raw now, I just don't use wet coal..

[old rascal]

Don't sell yourself short, asking advice and or otherwise collecting information doesn't put the decision making in someone else's lap. You're making and adapting your tools

 

The mix dried chalky and crumbly because it's just dry clay, unless you fire it it'll always be friable and water soluble. It's only purpose in the forge pan is as a heat shield. If you poke and scrape it, it'll gouge and scrape leaving loose dust and grit. Just take it easy on the forge table and it'll last a while.

 

The problem with using mortars is they will glue themselves to the forge pan so when they wear out and you need to replace it you'll be spending a lot of time getting it out. the mortar mixture recommended on the fire clay bag is for laying brick fire places, BBQs, fire pits, etc. not forges. That mix will withstand wood fire temps with minimal chance of the portland cement spalling but running the temp higher and I don't think so. The forge WILL get hotter around the air grate and the heart of the fire.

 

Just so you know, I'm a propane forge guy, I've used charcoal and coal, even have a couple few solid fuel forges around but I'm primarily a propane guy. I did spend a number of years working in the State materials lab where you can ask darned near anything having to do with construction materials and if somebody doesn't know the answer there's a book on the shelf. Believe it or not, I did indeed look up how to mix a refractory from fire clay. It's been WAY long ago I did it but the recipe isn't a formula there's wiggle room so the recipe I posted is close enough to work. Probably NOT in a ceramic kiln but maybe, I'd have to bug one of the guys where I used to work to look it up for me for hard numbers.

 

If you want good hard numbers hit the library and check out a kiln making book or have them do an inter library loan and get you a copy. Humans have been making kilns for thousands of years and they typically take much higher heat than a forge.

 

Frosty The Lucky.

I finally found some fire clay. In my area (Northern Illinois) it's nonexistent except from a masonry supplier and very pricey.and a two or three week wait. I want to hit metal. I thought and figured out who uses it. Potters use clay and after a few phone calls was directed to a pottery supply house where I purchased a bag. He also gave me a recipe to mix it that they use to line kilns. I'll give it to you and would appreciate thoughts on it before I mix.

 

! part clay

1 part portland cement

1/2 part sand

2 parts coarse sawdust

2 parts vermiculite

 

I asked about the sawdust and he said it was to keep it a looser mix. As this will not be applied vertically i wonder if it's needed or maybe more vermiculite.

I wish I'd found this site years ago and I'd be way ahead of where I'm at.

[Charles R. Stevens]

Your making a pot, not an insulated kiln. Besides the Portland cement deter images under heat (it turns back to cement) if you insist on a admixture use water glass. Clay and sand, or clay and grog (ground up fired clay) any wear from 70/30% clay to sand to 30/70% clay to sand will work. I'd go with the fat mixture.
If your looking for a home brew refractory try http://ezinearticles.com/?Depression-Refractory-Mix-For-The-Backyard-Foundry.&id=85797. But in truth clay and a bit of sand just narly moist. Say dryer than moms cookie do, rammed in with a wooden mallet.
I'm getting as bad as Frosty, I should have just just posted, "what Frosty said" and been done with it.