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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.
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?
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.
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.
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.
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.