Medium vs Fine grade Vermiculite?

[Neil2]

Re: Medium vs Fine grade Vermiculite?

"Same thing. 2" vermiculite/portland cement and 2" concrete on top?"

No.

The suspended structural slab should be 4 inches of reinforced concrete. Then 4 inches of vermicrete (5:1 mix) on top of that, then the hearth bricks. The insulation layer over the dome should be 4 inches of vermacrete (12:1 mix).

You can start with the vermacrete over the structural slab after one day. Keep the structural slab (and subsequent vermacrete layers) continuously wet for at least seven days - preferably longer.

[Rolaed]

Re: Medium vs Fine grade Vermiculite?

Thanks Neil;

Do you put the 4" Vermiculite on the base slab in one application? Or several applications?

The vermiculite on the dome, can you put stucco on top of it? I never dealt with Vermiculite before. Does it harden?

[dmun]

Re: Medium vs Fine grade Vermiculite?

Do you put the 4" Vermiculite on the base slab in one application? Or several applications?

You can do both layers at once, No need to let the support slab set, even. It's the same stuff as the structural concrete, just a different aggregate. Most people do it in two batches, because it's a lot of work for one day.

The vermiculite on the dome, can you put stucco on top of it? I never dealt with Vermiculite before. Does it harden?

In the course of a week the vermiculite concrete sets to a cork like consistency. It will be crumbly at the edges, and for this reason you may not want to have it exposed on the exterior of your structure. You can put stucco directly on the cured and dried vermiculite concrete. It's suggested you wait a month or so for this step to assure your dome and insulation is dried through.

Please ignore the poster above who suggests two inches of concrete and two of vermiculite concrete under your oven floor. This is half what you need of both.

[yorkyboy]

Re: Medium vs Fine grade Vermiculite?

yea mate,make sure the dome is well mortared,as in the gaps around the bricks are all filled,next thing is mix the vermiculite with portland cement i use a mix of 5 to 1, 5 vermiculite to 1 cement,mix till it is a oatmeal consistency,just so it holds together,or you can put the vermiculite only in mums old pantyhose legs and wrap around the dome like a sausage,you will need about 10 legs to do this,then pat it down so it is about 40-50mm thick,then appy chicken netting and then mortar and then render with a final coat,

[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.

[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?

[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.

[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.

[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.

[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.

[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?

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

[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

[david s]

Re: Medium vs Fine grade Vermiculite?

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

[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.