Blanket vs loose insulation

[ShannonCorum]

Is it better to use a blanket (HF10, ceramic, etc.) or loose vermiculite. Or should I use both? I currently have a double row of firebrick dome (one laid flat and the outer on its side for a thicknness of about 7 1/2 inches with mortar). Yet I have no heat retention. My oven will not get any hotter than about 500. The floor is a solid row of firebrick laid flat on about 3/8 inch mortar, so about 2 1/2 inches plus mortar. I don't know what else to do but build an outer frame and add insulation over my dome.

Any other thoughts on why my oven won't get hot?

Shannon

[azatty]

You have a tremendous amount of thermal mass, which means you need a tremendous amount of heat to get it to temperature. You need to insulate the oven. Period. I suggest using ceramic blanket because it is designed specifically to insulate (obviously). You can use loose vermiculite, and the early builders here did so with great success. As material sourcing became easier, most have shifted to blanket over vermiculite. However, there may be cost or sourcing issues that cause you to choose one over the other. You can certainly use both; blanket in contact with the dome and loose fill around it.