Stucco plus Vermiculite?

[MrBones]

I am preparing to render the first coat of stucco over the insulation for the Giardino kit. I planned on following the instructions on the YouTube channel which call for using a base coat and then a finish coat of stucco, however after reading many suggestions in this forum I am starting to think that I should be using a base coat of V-Crete. How important is the V-Crete? Can I add just vermiculite to the base of stucco at a 2 to 1 ratio (Or some other ratio) or should I make the extra effort to make the V-Crete?

[Gulf]

Hi MrBones,

Welcome to the forum. Vermicrete or perlcrete have been used to help "true up" the shape of a dome as well as for added insulation. It is not absolutely necessary. You mentioned the instructions on the youtube channel. I hope and am assuming that you are referring to the Forno Bravo youtube Channel. Forno Bravo recommends a two layer stucco process for their ovens. They also recommend that the two layers be applied over lath. If you follow their instructions you will be fine. Some of the discussions that you may have followed may have shown some who have chosen to use chicken wire over the blanket insulation for which to apply vermicrete. That is ok. Some of the discussions that you may have followed may have shown some who have chosen chicken wire for which to apply stucco. Maybe not so ok.

Imo, stucco needs to be applied over lath or a similar knit mesh wire. If not, make sure that you are using a stucco which has fiberglass fibers added to the mix and go the extra three step (scratch. brown, and finish coat) process.

1, How to Insulate, Shape and Lath Your Dome.
2, Stucco-First Coat-Day 1.
3, Stucco-Second Coat-Day 2. .

Don't try to add vermiculte to the stucco base coat. If you decide to apply a vermicrete layer apply it at about 8-1 vermiculte to portland cement. You can get away with making it a little stronger since you already have enough blanket insulation to insulate the dome. But, the stucco layer still needs to be applied over lath or mesh (not chicken wire). It will also need to be spaced away from vermicrete, since that layer will not compress slightly like the blanket insulation. If the stucco can't penetrate and surround the lath, it is not reinforced. This is where added fibers come in to play to make up for short cuts on proper installation. I'ts either one or the other to prevent cracking stucco imo.

Also, the only thing that I can see as an improvement to the Forno Bravo lath video is protruding and shaping a lip and reveal to accomodate a storm door.

[MrBones]

Wow, you have saved me a ton of research. Thank you so much!

Yes, those are the videos I am referring to. I will be sure to get the lath now (was planning to use chicken wire or welded wire that I have on hand) and can start this weekend. Forgive for asking, but what is a "storm door"?

Couple more questions, my hearth is 3 1/2 inches of concrete and then topped with another 3 1/2 inches of v-crete. When I go to set the screws for the lath should I screw them into the v-crete or should I drive nails into the FB board like they recommend in the Melbourne Fire Brick Company instruction/videos? Also, why do they mortar their fire brick floor when Forno Bravo just says to use sand to level?

[Gulf]

I would put the screws in to the vermicrete if it is possible. However, I'm not sure if you mean inserting them vertical or horizontal. Some pics of your build would help.

I'm not familiar with the Melbourne brick Company videos. But, firebrick expand and contract with heat cycling. We like them to settle in to their "happy places" and let the ash fill in the spaces. Also, many builders do not use anything to level the firebrick. If the insulation layer is flat and the brick are uniform, it is a waste of time and effort imo.