Quick question. Need a quick answer please

[whitewill1412]

If I add this extra layer of insulation in the bottom of the forge will it be good or bad?

[Goods]

Looks ok to me, if you loose the fire brick, but you still should rigidize and coat the blankets with refractory, with a final top coat of a re-emissive coating (like plastic).

Be careful about loosing too much volume in the forge. There is a certain balance between burner capacity and forge size… The fire brick takes up a lot of space and absorbs a lot of heat energy (at least while heating). 1/2” of Kastolite 30 on the floor will give you a very durable surface that is insulating, not just heat resistant. 1/8”~1/4” on the wall and ceiling will give fiber encapsulation and enough durability. The Plistix over the Kastolite will help super heat the forge…. and give even more protection from flux (if you start forge welding, flux will eat straight through ceramic fiber and fire bricks).

Keep it fun,

David

[whitewill1412]

I went ahead and did it.  Added thicker bottom and doused it all with rigidizer 

Since I already rigidized should I get the plistix to seal it better?

[Mikey98118]

Yup Most of us here on IFI suggest Kast-O-lite 30 or a high alumina kiln shelf for the forge floor; either one will end up about 1/2" thick, and serve the purpose. The Kastolite provides better insulation than a kiln shelf. The kiln shelf provides a smooth flat surface to rest any internal baffle wall on; either one needs Plistix 900, or one of the other finish coatings to help reflect heat back into the forge interior from internal surfaces. You also want to use Plistix to cover the rest of the internal surfaces.

Goods is correct; you don't want to lose any more internal height in that forge, or atmospheric circulation will suffer. Lose the brick.

[Frosty]

Oh yeah. Silica rigidizer has a fairly low melting temp, that's why firing it to orange heat makes the ceramic blanket rigid, the silica collected at the intersections of fibers melts and encapsulates them in glass. 

Plistix 900F will work well as the next layer in your forge liner but it's more properly a "kiln wash." Kiln washes were developed to prevent pottery and glazes from firing to kiln furniture, they are generally chemically inert and fire hard and slick like a coffee cup. Plistix 900F is a poor thermal conductor so it doesn't conduct heat into the material farther from the flame but continues to absorb energy making it hotter than just the hard refractory would be. 

Kastolite 30 li is rated to 2,600f continuous duty and being high alumina is resistant to caustic erosion. Part of it's aggregate load are evacuated silica spherules which serves two purposes they decrease the refractory's ability to conduct heat (insulation) and secondly they make a physically lighter refractory. 

Kastolite or other hard refractory isn't necessary if you apply a few layers of Plistix 900f but Kastolite 30 is concrete hard and strong at 2,600f so it will take a lot of physical abuse, more than Plistix and it costs less.

Frosty The Lucky.

 

[Mikey98118]

A third advantage about all the spherical voids that those silica bubbles leave behind in cast refractory, is that they provide innumerable stopping points for cracks. Before silica bubbles and alumina bubbles started being included in refractory, fractures were a big problem in forges, because of the fast heating and cooling cycles; this is not true of glass or ceramic furnaces.  And no longer a problem with Kast-O-lite 30, and other cast refractory that have the voids built in