Cultured stone outer covering

[madspeed]

Howdy, in the final phases of my barrel vault oven. I've built several curing fires and had a successful pizza night with family and friends. Now time to finish her up. I have a large bag of vermiculite i plan to mix with portland to create an insulating layer over the vault. My plan is to then cover with the same cultured stone I'm using on the fireplace, keeping the barrel vault shape.

Question is, can i use my standard stone mortar directly over the vermicrete or do I need to use some other type of mortar skim coat? Should I allow the verimcrete to dry a week or so before adding the stone covering? Haven't seen much info surrounding this other than for those that will be using a stucco finish.

[david s]

You’ll need a min of 3” (10:1) vermicrete preferably 4”. It is better to have a layer of blanket over the arch first, because it is dry, a superior insulator and acts like an expansion layer. Because vermicrete contains so much water it can swell when heated so is better dried off in subsequent layers.