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Only Castable Refractory insulation

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I bought refractory to fully line my forge no kaowool or anything else. How thick of a layer do I need to keep it insulated (I known refractory isn't the best insulator) and make it solid ?

This is what I got   Link to commercial site removed per TOS.

Edited by Mod30
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That isn't castable refractory, it is refractory cement. I've never seen it successfully used for casting monolithic shapes, though the Amazon post seems to indicate that it would be.  Perhaps it is different from the Rutlands cement I've used in the past.  The one I have used works great for a skim coat on knives that you are trying to quench for a hamon (with right selection of steel and application of the "clay"), but I would never use it for a fully cast forge.  If nothing else, it is only rated to 2,200 deg. F and the flame face will need to take well over that.

The Amazon post indicates that the Rutlands material has a 100 lbs/Cubic foot density.  Kastolite is fairly comparable at 90 lbs/cubic foot.  That might give you an idea of how much you would need in comparison to the Kastolite (see below).

If you want to build a monolithic cast forge I recommend a high alumina castable insulation product like Kastolite 30.  You can get it from High Temperature or on this site here (I would use at least a 2" thick casting of Kastolite for a forge, and wouldn't balk at 4" thickness):  


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In his defense, he did give the information on the Rutlands Castable Refractory Cement in the deleted Amazon link.  As a new user he likely wasn't aware that the TOS are actually enforced in this forum, as in most others they are only loosely adhered to.

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Welcome aboard Forger 29, glad to have you. If you put your general location in the header you'll discover how many members live within visiting distance.

NO, there is a world of difference between refractory CEMENT and Refractory. Cement is formulated to stick things together like bricks and has a short life in direct propane flame contact. It WILL NOT LAST as a propane forge flame face.  

Applying cements in thick layers is a guaranteed failure mode, it WILL shrink check as it dries, just like a mud puddle cracks as it dries. 

Do some reading in Forges 101 section for in depth discussions about forge building and the reasons. If you want to get it right with a minimum fuss pick a proven set of plans and follow them. do not mix different sets of plans or alter them until you have a good handle on what and how they work. It's not as simple as the IdJits on Youtube think.

Frosty The Lucky.

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