Vermiculite cement ratio question

[WoodchuckDad]

I have seen 5/1 and 6/1 suggested on this site. is that by volume? should I take a small pail and do 5 pails vermiculite to 1 pail portland cement?

[Tscarborough]

Re: Vermiculite cement ratio question

8/1 can also be used. I had the chart showing the properties of the various mixtures linked on a thread here a while ago. Here is another one:

[lwood]

Re: Vermiculite cement ratio question

Great info, thanks TS.

[dmun]

Re: Vermiculite cement ratio question

The higher proportion mixes, (I've heard as much as 10:1) require power mixing of the slurry, and adding it to the lightweight aggregate.

Thanks, Tscarborough, for that chart, which gives exact water amounts. It also confirms the 1:1 ratio between aggregate and finished volume.

[kebwi]

Re: Vermiculite cement ratio question

I used 5:1, 8:1, and 10:1 and didn't power mix any of it. Of course, I might have done it wrong. I put the dry materials in a garbage bag and "shake-n-baked" it lightly with a lot of rolling and tumbling. Then I poured the water in and mixed it up in a wheel barrow with a trowel and my bare gloved hands (working up to the elbows), gently mixing it all up, scraping the sludge off the bottom of the wheel barrow, and slowly infusing the mixture.

Despite a lack of power mixing, it seemed to work fine for me.

[Tscarborough]

Re: Vermiculite cement ratio question

Note also that unless your oven is 20 feet tall and built from solid gold bricks, your slab loading will probably not exceed 20 PSI.

[WoodchuckDad]

Re: Vermiculite cement ratio question

That chart threw me for a bit. I had to go back and reread a lot of things. So to clarify, I don't see sand as part of the hearth insluation layer recipe, just portland cement and vermiculite. am I on the right track?

[Tscarborough]

Re: Vermiculite cement ratio question

Yes, no sand needed. Perlite is an aggregate.

[WoodchuckDad]

Re: Vermiculite cement ratio question

how long do you wait afterpouring for it to cure before moving to the oven dome?

[dmun]

Re: Vermiculite cement ratio question

One week, more or less. If you pack in vermiculite on Sunday, you're probably fine to level and lay your floor the next Saturday. As Tscarborough says, even the weakest mix has lots of compressive strength for your application, so even if it isn't at absolutely full hardness it shouldn't be a problem.

[ckdickerson]

Re: Vermiculite cement ratio question

I poured my perlite mix Sunday and by tuesday it was as hard as concrete, no pun intended. Some more experienced readers may be able to give you an exact length of time. I will say don't worry when on the second day it still has the consistency of a rice krispy treat because it will, but another day or so and it will become very firm.

view my oven at:
http://www.fornobravo.com/forum/f21/...cky-12829.html (42" Pompeii in Kentucky)

[Tscarborough]

Re: Vermiculite cement ratio question

I wet-laid firebrick on mine the next day, but if you are a worrier, wait a week or a couple of days. Concrete (or perlcrete or vermicucrete) does not reach final strength in a linear fashion, it is at better than 50% within a day and 80% within a few days.

It is common to lay CMU walls on concrete that is a day or 2 old. It all depends upon the calculated loading.

Caveat: Done correctly. Allow for error if in doubt.

[Raffy]

Re: Vermiculite cement ratio question

Hey Tom,

Very interesting chart. Lot of useful information there. I'm definitely saving this info for the next build

[WoodchuckDad]

Re: Vermiculite cement ratio question

I was going to pour the vermicucrete 2 days ago but we had a strong storm system come thru and it's been raining on and off ever since. I was outside working with a flashlight till 11 last night getting my form all set up. Unless there is another downpour tonight, I will be pouring the mix then. I am going to do 5 inches of 7-1 mix. Then I have to find something else to do for about a week while I let it set up properly. Guess I can cut my firebrick this weekend.
Thank you everyone for all the advice.

[WoodchuckDad]

Re: Vermiculite cement ratio question

I did the pour tonight. Just barely beat the thunderstorm that rolled in(I covvered it before the storm came.) Shouldn't call it a pour....more of a shovel. kind of like shoveling S#%t.