Medium vs Fine grade Vermiculite?

[Neil2]

Re: Medium vs Fine grade Vermiculite?

A 4 inch suspended slab with about 1% rebar by volume is plenty strong enough (0.5 % each way). Do some research or get advice on rebar placement. Do not have "loose ends". Rebar ends should have a hook or a 8 to12 inch right angle bend.

[thamnophis]

Re: Medium vs Fine grade Vermiculite?

I'm glad I found this thread. I've been waiting for days for my 5 inch vermiculite layer to dry rock hard. It is indeed a bit spongy or cork-like. I guess it is time to get back to work!

[dmun]

Re: Medium vs Fine grade Vermiculite?

4x8x16 cement blocks under the cement base hearth for support. I do not feel too comfortable with the rebar supporting the weight of the entire oven and dome.

You are of course welcome to do anything to increase your comfort level, but you really don't need to worry about the support of the dome. First of all, it's over engineered to begin with, and second of all, most of the downward forces are on the periphery of the dome, the floor and insulation in the center are lighter weight by comparison.

There are lots and lots of ovens completed, and only a handful have center supports under the dome.

The vermiculite concrete hardens, but it's not rock hard. "Cork like consistency" in how it's usually described, meaning it can flake off at the edges. It has more than enough compressive strength to support your dome. Again, it's a technology that has been widely tested and supported. They make swimming pools out of the stuff, and man, water is heavy.

[GianniFocaccia]

Re: Medium vs Fine grade Vermiculite?

I do not know about freeze-thaw properties, but you do not need any block to augment the strength of the support slab. A 4" thick slab with rebar spanning your block stand is sufficient. It might be advisable to let your support slab concrete set up a little (next day) bit prior to pouring your vermicrete insulating slab. Vermicrete dries to a firm, but spongy texture that can be easily scraped away with a fingernail, but is plenty strong to support a floor firebrick lying on it's side.

[Rolaed]

Re: Medium vs Fine grade Vermiculite?

I have poured the foundation and this weekend will set in the cement blocks. From what I have read, it is advised to have a "floating base". I live in Michigan where we get plenty of snow and cold. I am thinking of running some 4x8x16 cement blocks under the cement base hearth for support. I do not feel too comfortable with the rebar supporting the weight of the entire oven and dome. Your thoughts are appreciated.

So after the cement blocks are laid, I will put a piece of plywood to pour the concrete into. Then ater that, teh vermiculite mix goes in.


Also, does the vermiculite/cement mix harden or does it stay spongy. My plan is to pour the cement base and the vermi/cement in one application. If the vermi-cement stays soft, doesnt the weight of the firebrick cause it to deflect and sink in? Maybe I am asking dumb questions but I would rather feel safe than sorry.

[david s]

Re: Medium vs Fine grade Vermiculite?

Sorry I just answered a question on p.1 of this thread.

[david s]

Re: Medium vs Fine grade Vermiculite?

The insulation layer goes in between the supporting slab and the floor and between the inner dome and the outer render/stucco

[aeu99217]

Re: Medium vs Fine grade Vermiculite?

sorry, i thought you were talking about the high heat mortar

[dmun]

Re: Medium vs Fine grade Vermiculite?

Fireclay is a standard masonry supply item in the US. You have to go to a brickyard: the big box stores don't carry it. If for some reason you can't get it there, a ceramics supplier will have it, as will the refractory dealer that will handle your board and blanket.

It's not a rare substance. Make some phone calls.

The leveling medium under the firebrick floor is one to one fireclay / sand. You can lay it dry, and wet the floor after you have it the way you want it, or mix it with water and use a notched trowel to apply it on top of the vermiculite concrete.

Vermiculite or perlite can be had from a wholesale garden supplier, or a pool builder. As aeu says, you can get it online if local suppliers fail.

[aeu99217]

Re: Medium vs Fine grade Vermiculite?

mortar mix is 1 fireclay, 1 portland cement, 1 lime and 3 sand. Not sure if there is another name. Here in the uk i have found a supplier that sells it all CF Boards : Kiln Linings, Best Site for Kiln Maintainance and Repair Materials

You should be able to get vermiculite from a horticultural website, dont think many building merchants do it.

[Rolaed]

Re: Medium vs Fine grade Vermiculite?

What is the ratio for the fireclay mortar used under the firebricks? 1:1 with sand. Anything else goes into the mix?

Is there another name for fireclay. Some of the material called out in this project is tough to come by!! When I call and ask about vermiculite, I get pauses as people never heard of it.

[leckig]

Re: Medium vs Fine grade Vermiculite?

I just realized that besides garden centers stores selling hydroponic supplies are excellent source of both vermiculite and perlite.

[Neil2]

Re: Medium vs Fine grade Vermiculite?

"mixing the vermiculite with the concrete on top of that."

Absolutely not. Mix the vermiculite/perlite with cement not concrete.


"The only Vermiculite I can find is mixed w/ Perlite. "

That will work just fine. I mixed perlite and vermiculite for my dome insulation layer.

[ByronD]

Re: Medium vs Fine grade Vermiculite?

The only Vermiculite I can find is mixed w/ Perlite. Can I still use this in my Hearth?

[Rolaed]

Re: Medium vs Fine grade Vermiculite?

Thank you so much. I live in Michigan and looks like you are in Jersey where the climate is similar. I started the excavation this week. The city inspector told me to dig 42" deep footers for the oven support. It is a lot of work but work is underway. Not sure if you had to do the same for your oven. Maybe it is overkill, but sounds like I need to go below the frost line to ensure the slab is not lifted in the future.