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Mojoe 08-25-2007 04:10 PM

Vermiculite Layer
Does the vermiculite layer require any particular curing method? Cover, wet cure, etc like concrete?

I mixed the vermiculite 5:1 and wet it enough to form a loose ball in my hand but no water came out and I wasn't very gentle with it, hoe and wheel barrow. Will it be okay?

Unofornaio 08-25-2007 06:55 PM

Re: Vermiculite Layer
It should be fine. Don't fool with it, its deceiving just when you think its not going to ever set up it does. Give it a few days

Mojoe 08-25-2007 07:50 PM

Re: Vermiculite Layer
Just poured it earlier today and there's a chance of rain so I threw a tarp over it. I think my problem is that I used the fine vermiculite and when I run my hand over the top it comes right off. No clumps, just small particles. But if I push on the layer it feels as most here have described, spongy,springy, etc.

nissanneill 08-26-2007 05:10 AM

Re: Vermiculite Layer
Yes, it is unusual material to work with. When I poured mine, I added enough water to squeeze just a little bit out with a clenched fist. See my post on:

permalink #2 for the description and pictures. It will set in a few days and will feel a little like a firm cork consistency


Mojoe 08-26-2007 01:46 PM

Re: Vermiculite Layer
The particles in mine aren't that big and my mix wasn't that wet. Mine is close to a really coarse sand. A day later and it is like a firm cork (perehaps harder) however if you gently and barely slide your hand across the surface the result is a hand full of small particles and a irregular finish. The finish on this layer is closer to cornmeal on a pizza peel than a rough concrete finish.

How long do I wait before I remove the forms?

nissanneill 08-26-2007 03:20 PM

Re: Vermiculite Layer
so long as the layer 'sets' over the next few days (should be close to set by now), it will be fine as the hearth bricks will sit directly on it. I wouldn't worry too much about the surface toughness BUT the vermiculite which will lie beneath the dome brick course (soldier bricks on the first course) will need to be quite firm in order to support the weight of the dome.
Are you planning on running your hearth bricks out and under the dome bricks or cutting the hearth to fit inside the first soldier course?


Mojoe 08-26-2007 03:55 PM

Re: Vermiculite Layer
Haven't decided yet, originally thought I'd run the bricks out and under. Should I give it a couple days before I pull the forms?

Unofornaio 08-26-2007 04:04 PM

Re: Vermiculite Layer
Yes wait to pull the forms. No need to do it now and run the risk of pulling off chunks of the sides. As I said before, don't fool with it and give it a couple of days. If its been raining there Id give it the better part of the this week, wed or thurs to be safe.

Mojoe 08-28-2007 08:40 PM

Re: Vermiculite Layer
Came home from work today to find out that my 2 1/2 year old did some excavating on the vermiculite layer, about a 6"x6" square. It appears I didn't add enough water as the top 2" easily crumbled upon removal. The bottom 2" that was closest to the fresh concrete was actually very hard, used a heavy piece of scrap 1/4" angle to scrap most of it off.

With the new batch I placed tonight I added enough water so that a little would ooze out when squeezed. Much more than that and the stuff wiggled like jello when placed and troweled. Feels like I got it right this time.

james 08-28-2007 11:01 PM

Re: Vermiculite Layer

I'm sure it will set. Gravity is on your side as well.

I have always thought of the mixer as feeling like a grainy oatmeal.

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