New member, new build.

[The foxdale phantom]

Hand mixed the perlite/vermiculite/cement mix at 2.5 : 2.5 : 1. Bucketed it up to form and screed off. The added weep holes worked as expected. Will leave now to dry out before adding a fine layer of bedding sand to lay floor bricks.

[UtahBeehiver]

Just a heads up. You are putting a lot of effort into this build and we all want the oven to be a success. I am concerned that the 2.5 to 1 pcrete ratio is not going to give you the needed insulation in the floor. I sent out a post showing the K values of pcrete and recommended 5 to 1 with a min of 4" with 6" better since it takes almost twice the thickness of pcrete vs CaSi board. This post, unfortunately went out when the site was hacked so I do not know if you saw it or not. There are a couple options, add another more pcrete (5 to 1) or add layer of CaSI. Proper floor insulation as well dome insulation is key to an effecient oven. Just trying to watch out for you and all your hard work.

[The foxdale phantom]

So UtahBeehiver the mix I have done of perlite/vermiculate (5) to cement (1) won’t be sufficient?

[UtahBeehiver]

In the post, I thought it said 2.5 to 1 not 5 to 1. 5 to 1 is the correct ratio structural rating for a floor. It has a K value of around 0.72-75ish with CaSi having a K value (depending on temp) of around 0.5. Our rule of thumb (conservative) is twice the thickness of pcrete to CaSi thickness. Bare minimum floor thickness of 5 to 1 pcrete is 4" if the ratio is 2.5 to 1 then the K value really shoots up. If it was a typo on the post 2.5 to 1 and is really 5 to 1 ratio you will be at the minumum recommended floor insulation.

[UtahBeehiver]

I went and read the post closer, so it is 5 to 1 half perlite and half vermiculite to portland. It will still be at the lower end of the insulation scale. If you are wanting to do serious extended cooking, brick heat saturation is most important with minimum K value. The insulation on current oven will be fine for pizzas and some extended cooking. So it is up to you. Sorry I misread the post.

[david s]

Because a vermicrete/perlcrete mix requires so much water in the mix there is more than double that which is required for adequate hydration, so damp curing to enhance strength is less of a problem. It is the elimination of the freee water that is the greater problem. Read my attached experiment on drying a vermicrete slab.
If it were mine I'd be covering it for a few days to hold the moisture in the surface, then allowing sun and wind to do its thing for a couple of weeks before covering it with floor bricks.

A 5:1 vermicrete is not quite as good an insulator as calais, whereas at 10:1 it's equivalent to blanket and calais, but not strong enough to support the weight of the oven and floor. That is why we recommend 5:1 under the floor, but 10:1 over the blanket if you want the superior insulating quality.

You will need to decide if you want the dome outside the floor or on top of the floor. There are pros and cons for both methods, discussed somewhere on the forum. My preference is to build the dome on top of the floor which reduces the need for very precise cuts at the perimeter of the floor bricks.

Vermicrete insulating slab PDF.pdf

[The foxdale phantom]

After reading your post UtahBeehiver I decided to put my form work back on and raised it an inch above existing Perlite/vermiculite base , I then made another batch of 5:1 perlite cement to go on top. Having not quite enough to do the front landing again I went with a vermiculite/fine sand/cement mix to finish it off. If anything the floor height is a little higher which is a good thing for me. DavidS I am having the outside of the dome on top of the wfo brick floor.