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I've started laying out on paper the exact dimensions of my forge..........showing the inside measurement of the 12" pipe and the 2 1/2" thick K-26 soft brick all the way around.  What I end up with is a forge cavity sized 6 1/4" x 6 1/4 x 17".  Now I need to decide how thick to cast the KOL30.  Originally my thought was to cast 1" thick all round.  But that would only end up giving me a 4 1/4" square cavity.  My primary purpose for building a forge is to make knives.  I eventually would like to be able to forge weld (fake damascus) blades.  So will a 4 1/4" square cavity be large enough to do that???   I'm thinking maybe not!  So would 1/2" on the side-walls and ceiling of the forge and then 1" on the floor still give the brick plenty of protection?

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For my floor I have a little over 1/2 inch.  For the walls and ceiling areas it's around 3/8 inch.  Some people go a little thinner and some go thicker.  An inch on the floor and half inch on the walls is more than enough protection in my opinion.  The more mass (thicker layer) you have in your refractory, the longer it will take to heat up the forge.  However, once it is up to temperature, that same mass will maintain the heat better than a thinner shell and that can cut down the reheat time a bit.

If you plan to forge nothing but straight, or nearly straight, blades then you really don't need much width.   On the other hand if you anticipate forging some more interesting shapes for knives, axes, or other non-linear items you'll probably want some extra width.  I'd go with the thinner walls and a little more wiggle room in the forge if I were building using those materials.

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Thanks for the comments.  I'm going to be applying Metrikote on top of the KOL, (an IR reflective material) so I don't think the KOL will absorb as much heat as it would without.  I don't ever envision myself forging an axe head.  But if I needed to do something that large, I could easily build a coal forge.

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FWIW I use Matrikote as well and I do think it's a worthwhile layer, but the material under it still gets really hot.  Beyond the IR reflective capability it is noticeably more resistant to flux than naked KOL.

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1/2" is  more than enough Chris. Matrikote doesn't contain zirconia so it's not a more IR re-radiator than KOL. What it is is more chemically inert and has a much finer pore structure and it's significantly harder. Mix it about like latex paint and apply it in several thin coats allow it to dry between. Thick layers of Matrikote or Plistex are much more likely to flake off.

If you want to reduce the volume of your forge just lay more "treated" K-26 in it to take up volume. By treated I mean a layer of KOL and Matrikote.

Frosty The Lucky.

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Yeah, keep a number of treated IFBs handy so you can make it shorter, narrower, lower, etc. as necessary. 

The variability is what I really like about a rectangular forge.

Frosty The Lucky.

 

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