Concrete/Vermiculiate crumbly

[Roadkyng]

I have my stand complete and ready to begin building the oven. My concrete/vermiculite layer is 8" thick. It is encapsilated on each side by regular concrete. The one issue I have is it seems to crumble off fairly easily. I realize it's just an insulating layer so strength is not that big of an issue. It's compression strength seems to be fine. (will compress if pushed in firmly).

My question is what can I use to smooth the insulating layer and adhere the brick floor to it? I figure the regular fireclay mortar mix but am not sure what thickness (standard 3/8" mortar joint?)

Is this regular behavior? I used the the recommended 1:4 ratio of concrete mix to vermiculate

[geisen]

The vermiculite is crumbly but sets up better in a couple of weeks.
I agree, weird texture but just go with it.

do not mortar the bricks to the insulating layer.

from the directions.....

"With this method, you do not mortar the bricks in place, but rather spread a thin layer of paste made from sand, fire clay and water as a "bed" for the floor.

To make the under floor paste, mix 1 part fine sand and 1 part fireclay (photo 2) with water until you reach the texture of a sticky mortar (but without the cement). Spread the under floor using a notched trowel as the ridges will make it easier for you to get your floor perfectly level (photo 3). The process is similar to setting ceramic tiles."

takes a leap of faith to work with some of these materials.

keep at it, you'll be cutting bricks in no time.

greg