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My consolidated notes for new forge builders

Lou L

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After countless hours combing the gas forge section of the forum I came to realize that much of the information required to build a basic forge was difficult to access.  It was spread out across a number of threads and much of it was “old information” as new ideas could be found in other places. For that reason, I decided to document my own journey and share my notes that I took as I found information.  This is what I gleaned from much reading.  I know that JHCC wanted these notes so I thought I’d share them with my own experiences. Here goes:


Materials for Gas Forge

Mikey’s summary of the whole thing:


Ceramic wool:

This is easy.  It is available online and from current members here.  I found a warehouse for Harbison Walker International a half hour from me and was able to get a large amount at a good price.  Go with 1” material at 8# density. It is best to use two layers rather than one 2” layer.

Measure the circumference of your forge substracting ½ “ from the diameter (half the thickness of your wool) and cut ever so slightly large.  This will create a fit that is tight enough to keep the wool rigid in place. Before adding the second layer I rigidized the first layer and burned off the water with my burner.  The color of the dye faded to white as the wool heated up. When it was basically gone I stopped the burner. It took about five minutes, maybe a bit more. The second layer is added using the same math measuring from the new, smaller diameter created by the wool.



I bought fumed silica on Amazon and made my own using Jasen’s recipe.

"...used a cup of fumed silica in a pint of water. Idk if it's proper amount but it worked very well on my forge."
Add a drop of food coloring so you can see the rigidizer and ensure coverage.

Per Frosty:  It’s is critical that you butter the wool by spritzing it with water prior to applying the rigidizer.  Do this for both layers. The rigidizer should run between layers and bond them together somewhat after the second firing.



This has been identified as a critical step in all processes of forge lining.  It is Frosty’s mantra.

“The ONLY thing I have to add to Mike's above post is about buttering. If you don't wet the surface before spraying the rigidizer it will dry on contacting the dry material. Capillary action can ONLY happen if it's wet enough to flow.”

“Interestingly enough the colloidal silica rigidizer is denser than water so as it flows through capillarity it will push the water ahead of it by displacement. It doesn't do this forever but it does allow the rigidizer to penetrate farther.”

“Buttering a hard surface is even more important as the rigidizer, mortar, etc. will NOT penetrate a hard surface it flash dries on the surface unless it's way too wet a mix. You want the rigidizer to penetrate the surface so it bonds properly.”

“Buttering is an IMPORTANT part of the process of getting stuff like a hard refractory flame face to bond solidly to a refractory blanket insulating liner. Getting the blanket to bond to the shell. and getting the kiln wash to bond to the flame face.”

“Heck, anybody out there throw pottery? What do you do when you stick the handle on a coffee mug? You wet the joint surface right? It's not quite as important on freshly thrown pottery as it is on masonry but it ensures a good bond none the less”


Link to Frosty’s forge lining directions:


Kast-O-Lite 30 curing instructions:
    Mixing instructions.  1 pound of kastolite gets 2.75 ounces of water.

This comes from Frosty’s NARB thread.  I found that measurement to be about right on my first try.  I found some detailed information from Harbison Walker that suggested 3oz would work.  I started with 2.75 by adding it very slowly and mixing a lot. I mixed it for five minutes or more and finally added a bit more water to get close to 3oz.  If you go over it will make the refractory too thin and weak when hardened. Be patient and it will suddenly switch from being too dry to being wet.

Cure it in 100% humidity.  I did this by putting a damp rag on it and putting it in a garbage bag for a day or two.  It should then be heated starting at 200 degrees for a couple hours to get remaining water out and then gradually increase the heat.  The final cure is done with incremental application of the burner. Some have used the burner to cook off the water carefully and skipped the oven.


The only thing I didn’t add to them was Frosty’s account for measuring quantities in the pouring of a ribbon burner.  Here it is:

”Current ribbon burner form gets 3 lbs of kastolite and 8.25 ounces of water”

Frosty found that measuring pure volume was not enough and he ended up having to mix another batch.  Figure out your volume and add a bit more to account for settling.  His measurement should get you darn close or right on though.

JHCC observes elsewhere: "I’d found in another thread the useful detail that since one cubic foot of mixed Kastolite weighs 90 lbs, that’s 19.2 cubic inches per lb. My [own] mold measures 7-3/4” x 3” x 2”, which is 46-1/2 cubic inches. That gave me a starting point of 2 lbs, 6-3/4 oz of dry Kastolite plus between 6-2/3 oz and 7-1/4 oz of water. It’s been very dry, so I ended up using very slightly more water (about 8 oz total) to get what felt like the right consistency."

Matrikote- How To Apply
It isn't intended as a refractory liner, it's a kiln wash. A product designed to be the final barrier between the fire and what's in it and the liner. Thick is counter productive, think of it as paint or like an undercoat, it's there to protect and radiate heat back into the forge more efficiently. MIx it to a consistency between thick latex paint and country gravy. Spritz the liner with water then paint it on.”     -Frosty

 This is a step overlooked by everyone I have seen on YouTube and most other sites except here.  It reduced the time to heat up stock by 20-30% according to anecdotal evidence from members on this forum.

Themal ceramic K26 brick.
Per Mikey “The 1" thick version of these bricks make the perfect transition layer to place between a high alumina kiln shelf and a pillowing layer of ceramic fiber insulation, to protect it from being overheated by the shelf temperatures.”


 Mikey uses K26 brick to create better forge floors. He also offers a more complex method using high alumina kiln shelf and refractory.  It is beyond me:

“Those wanting the most efficient floor possible will use small amounts of high alumina refractories in layers, starting with 3000 or 3200, then 2800, 2600, and finally 2300 refractory over ceramic fabric or board insulation. This scheme also allows the floor to be shaped, rather than flat.”


Wayne suggests using scrap ceramic wool and shaping it to create a “half oval (per Mikey) and then layering last-o-lite and kiln wash to avoid a flat floor and allow flame to flow.  This seems superior to a flat kiln shelf.

I found that this is too much for the average person (I’m below average and it’s way too much for me). I am settling on the strength of the kast-o-lite applied to a rounded floor.  I also picked up a gallon of moldable refractory from Harbison Walker that is rated for 2300 degrees and hardens like kast-o-lite. It can be applied like joint compound and I may use it for the forge walls instead of casting the whole interior.  I did make a shell out of metal flashing that will serve as my inside mold for casting the walls of the forge. The large opening for the ribbon burner makes casting the interior problematic. The mold is complex. This is why I may use the moldable refractory.


However, the K26 bricks appear to be the best thing on the market for covering the forge openings.  They are relatively cheap and seem useful to have around.


Alternatives to buying matrikote or plistix for lining the forge:

There is an active group experimenting with all sorts of cryptic, alchemical concoctions.  These are not for average (or below average) folk. Frosty does offer up one that seems doable:

Buttering surfaces during forge construction: by Frosty
“I mixed 2pts. Zircopax to 1pt. Cast-O-Lite 30. I added enough water to make a consistency about like latex paint and painted it on with a brush. Making it that thin means you have to mix it almost constantly or the zircopax settles out.

I believe this is his version of a final layer for lining his forges.  I do not have Zircopax and the additional cost of the bag of Zircopax is more than the small amount of Matrikote that I need.  I would like to hear from Frosty on this...I may have it wrong.


Propane regulator:

It must be adjustable minimally from 0-20 psi.  A shielded hose is ideal if you will not be using copper tube to the burner.  It is possible to use a long schedule 40 nipple on the end of your burner and orient it away from the forge opening to get the hose away from the heat.


Burner components:

There is so much information on the forums and it is specific to the type of burner you are making.  I made a ribbon burner and found all the parts I needed online at supplyhouse.


      I’m certain this is incomplete and welcome questions, comments, and challenges.   I’m just hoping to consolidate the most basic information for people trying to get started.



For the first of the many inevitable addenda:

I forgot to mention release agent when casting kast-o-lite.  It will stick to anything!  Readers who don’t diligently examine all the threads may follow the older advice for using spray Pledge or another waxy furniture polish.  Don’t do it!  

Use either cooking spray or crisco.  I used crisco because I felt I had more control applying it without making a mess...plus I had an old tub of it that wasn’t good for much else.  

Apply release agent to everything that will be contacting the wet refractory but should not be permanently attached to it.


Gas Forge Refractories and Supplies

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Thank you very much for this information.  Nailing down the rigidizer is giving me a fit.  There are a great variety of fumed silica products on the various markets.  Ensuring the product is hydrophilic proving difficult.  I realize that links to commercial sites are a no-no.  But, if someone would message me the name of a proven product I would greatly appreciate it.  Thanks. 

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I haven’t lined my forge yet, but on Lou’s recommendation, I got a quart of System Three white silica filler from Amazon. It’s under nine bucks. I’m told West Systems makes a similar product. 

Oh, and mentioning brands and suppliers by name is okay. It’s just direct links to commercial sites (outside of the Knifemaking Suppliers page) that are verboten.

I haven’t lined my forge yet, but on Lou’s recommendation, I got a quart of System Three white silica filler from Amazon. It’s under nine bucks. I’m told West Systems makes a similar product. 

Oh, and mentioning brands and suppliers by name is okay. It’s just direct links to commercial sites (outside of the Knifemaking Suppliers page) that are verboten.

And welcome to IFI! If you haven’t yet, please READ THIS FIRST!!!

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JHCC, thanks for the info.  Actually, I have been on IFI for about 5 years.  I just don't post.  Have been strictly coal.  Wanted to expand into propane.   I knew I didn't know anything about it.  After many hours of research, I'm starting to feel like I know even less than when I started.  =)


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JHCC, do you have a picture of what your mix looked like?  When I rigidized mine the color was very faint on the wool, still seems to have firmed it up.  Yours was a MUCH darker blue than I ended up with, wasn't sure if you added more colorant, or just used a whole lot more rigidizer than I did.


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I used a fair amount of food coloring and dabbed the  mix on with a long-handled paintbrush. (I just used the spray bottle to mist the wool with plain water before applying the rigidizer.) So, probably both. After firing, the color all burned away, with the exception of one spot on the bottom rim of the front opening; I'll be taking care of that later today.

(By the way, I used green food coloring and found myself humming Kermit the Frog's "It's Not Easy Being Green" as I dabbed the stuff on.)

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An update with more detail:

This post is just an example.  It is my response to the challenges I had before me.  Namely, I had to figure out how to cast the interior of the forge with kast-o-lite 30 and deal with the large rectangular opening for the ribbon burner.  In the end I chose to cast using a form made out of thin metal sheathing and a wood block shaped to fit the curvature of the metal cylinder.  Both were lightly coated with Crisco as a release agent.


I first cast the bottom of the forge and the back wall.  I did this by making a round band of the sheathing slightly wider in diameter than the rear hole in the forge and stood the forge up on its end with the sheathing acting as both a support and a form for the castable.  This allowed me to have the castable protrude past the outside wall of the forge in order to protect it from dragon’s breath.  The back is not pictured but you will see how I did the same with the front of the forge as well.

Once this casting dried (inside a plastic bag with a wet rag inside to keep 100% humidity), I moved on to the next step of casting the rest of the forge.  Tip: do the casting inside the bag so you can pull the garbage bag up around the forge easily and seal it once you are done.

Next, I stood the forge on end, inserted the wood block and the cylinder, and pressed the castable into the space between the rigidized wool and the metal form.  I used a stick to compact it in.  It took two pounds of castable to do the back wall and hole and six pounds to do the rest.  You will notice how I used a ring form (metal sheathing) to shape a projection out of the front hole of the forge.  I have no idea how well this will hold up in use but I like the idea of managing dragon’s breath and adding a modicum of volume to the forge.



Here is a better view of the front.  You can see the difference in the casting between the part that was formed and the area that was just free cast.




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The next problem was dealing with the hole for the ribbon burner.  If you are using regular burners I think it is easier to deal with.  This, I learned, is one small drawback from using a ribbon burner with this type of forge.  I could have tried casting the port for the burner when I did the interior but getting to all the areas and making the forms work was annoying.  Therefore, I chose to experiment with Inswool Moldable since I had picked up a gallon of it when I got the other materials.  Here is the hole after I cast the interior:


The situation, as I saw it, was that I wanted the burner to sit back a little ways from the interior of the forge and I wanted a tight fit to eliminate heat escape from the burner hole.  I decided to create shelves with the castable that would support the burner in the desired position and also create a gasket between the inside of the forge and the burner port.

This is the Inswool Moldable.  It is rated to 2300 degrees and creates a hard flame face.  It requires minimal treatment in terms of drying/cooking before it is ready to use.


It has the consistency of a light clay.  It is not as dense as clay...I guess it is more plastic.  I simply put on a rubber glove and formed it by hand.  It was quite easy and, if it works out with long use, promises to be a very useful material for making forges.

My cast shelf for the burner:


I wrapped my burner in plastic wrap and used it to shape the Moldable.  I ensured that the ports in the ribbon burner were not obstructed, of course.

The only other bit of work I did was to create a small ridge in the interior of the forge to act as a barrier from the swirling plasma in the forge.  I found in my test firing (while cooking the rigidizer on the wool) that the burner did not like being right in the line of fire.  I figured that the shelves setting the burner further back was the most important fix for the problem but decided that diverting the vortex away from the burner face wouldn’t hurt.  This is what I came up with:


The picture isn’t perfect, but you will see the small ramp/bulge at the bottom of the burner port.  This is a contiguous part of shelf casting, it is not simply attached to the wall of the forge.  The mass of Moldable looks large in the picture but most of what you see is just a light surface smear from my messy hands.  The raised lump is only about 3/4” wide and high.

It is entirely possible, and possibly better if this Moldable proves weak, to do this with kast-o-lite.  However, I really found my method to be very flexible 

I hope this helps someone.


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Great job Lou! This is a heck of a job of work, thank you! 

The only thing I'd like to add is regarding the "Zircopax + Kastolite" kiln wash experiment. It was just that an experiment and not a complete failure though the results weren't what I was looking for.

Oh WAIT! Okay, I thought of another thing that's more of a tip. Linoleum makes excellent form material. The shiny side is pretty non stick (Till I discovered Kastolite that is) and it's easy to cut and form. You can warm it up with a heat gun or in the oven (CAREFULLY!! :o) and make it easier to form. 

WHAT something more?  Flexible styrofoam type packing material is a good material to make a ribbon burner port in the hard refractory. You can stick it with contact cement or double sided tape and carve it to suit with a utility knife. Removal is as easy as scooping it out with almost anything. 

Again, thank you Lou!

Frosty The Lucky.

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Thanks guys.  Frosty, I have to admit that I was curious to hear your thoughts on the Inswool Moldable.  I need some real time on the forge to determine if the shelf/gasket  I formed works well.  Also, I have no idea if the baffle I made inside the forge adds up to nothing or if it will, indeed, benefit the burner.  You and a few others on here could help with insights on that.


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I don't know anything about insulwool Moldable, if it works I can think of all sorts of places it'll be perfect. I'll be watching for your results.

I don't know how your baffle will work, I'll be watching for your results on that too. Keeping the burner block as out of the heat as possible is something I'm always interested in. A: baffle or deflector or spoiler or ? to redirect the flame around the burner sounds like a good idea if it works. 

Frosty The Lucky.

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It’s enough for me to hear that both are viable options.  I planned on getting a thermocouple and PID to get temp readings on the forge.  When that happens I’ll try to take readings.  Other than that, I have no comparison forge to see if the benefit is real.   Once it gets seasoned better I’ll do some video for the inspection of the pros.

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