Quantity of vermiculite per sq ft for v-crete?

[mitch77]

HI,

Making plans and I could use some estimates.
I will be using course vermiculite.
I will be using one of the spare mortar recipes.

Can I get some estimates on how much Vermi I need per sq foot?

Thanks very much.

[david s]

Re: Quantity of vermiculite per sq ft for v-crete?

That all depends on how thick you want the layer. There will be about a 15% reduction in volume on mixing, so if you work out the dry volume add around 15%. I find that the course stuff does not hold together as well as the fine stuff for the same given amount of cement. I prefer a 50/50 mix of medium grade vermiculite and medium grade perlite.

[mitch77]

Re: Quantity of vermiculite per sq ft for v-crete?

OK,

This is for the base.
I have 5" of reinforced concrete and I want to put 6" of insulated
"vermi-crete" on top of that and then
the floor of fire brick and the dome oven over that.

I read the bigger the vemiculite the greater the "R" factor.

Please tell me what you think is best. Thanks

[Gulf]

Re: Quantity of vermiculite per sq ft for v-crete?

OK,

This is for the base.
I have 5" of reinforced concrete and I want to put 6" of insulated
"vermi-crete" on top of that and then
the floor of fire brick and the dome oven over that.

I read the bigger the vemiculite the greater the "R" factor.

Please tell me what you think is best. Thanks

That's easy, one square foot of a 6" pour is 1/2 of a cubic foot. Just figure your total square footage and add the 15% that David recomends. I do believe that he is correct on that figure, because I came up short on my pour.

The course vermiculite will probably be medium grade when you get finshed mixing. But, don't get into a discussion with David...............on the size of marbles .

[lwalper]

Re: Quantity of vermiculite per sq ft for v-crete?

If you're doing 10:1 ratio (which works really well), just mix 10 scoops of vermiculite with one scoop of cement. Figure how much volume is in that 10 scoops and divide that into the volume you need for the pour. It doesn't matter how big your "scoops" are as long as you use the same size scoops for each component. I used something like four cubic feet of the course vermiculite for a 4x6 foot pour.

I found too that it helps to moisten the vermiculite a bit before incorporating the cement; then thoroughly mix and dump it in your form. Don't get the mix too wet because the cement seems to wash off of the vermiculite and end up in the bottom of the wheelbarrow.

It doesn't look like much when you dump the mix in the form and you'll wonder if it will actually get hard, but it does harden up. Let it sit for a couple of days (or a week) before you try to do anything with it. You can damage it. Spread a layer (1/4 - 1/2 inch) of play sand over it for brick bedding before you lay your brick to even everything up. Use play sand (it's expensive per volume, but worth every penny and you don't need that much of it) because it has been washed and has all the little pebbles out of it that might cause a problem getting your brick to lay in there flat.

After the fact, I'm wishing I had put down a couple inches layer of ceramic insulation board under the vermicrete. I've got 130 degrees under the bottom of my oven. Just a thought.

[david s]

Re: Quantity of vermiculite per sq ft for v-crete?

The reason you have heat under your vermiculite is because it is still wet and wet insulation does not work too well. Eventually it will dry and it will then insulate ok. It is better to wait for a few weeks, if the weather is fine, before building over a vermiculite slab, otherwise you are locking in the moisture.

[lwalper]

Re: Quantity of vermiculite per sq ft for v-crete?

It's been three years and numerous fires later -- still 130 degrees. My oven is off the ground with an ash dump below. There's plenty of room to work underneath and I had thought to add some insulation under the support slab -- maybe some 6 inch fiberglass batting. The oven actually works great. I've just got a bit more heat leakage than I'd like to have for the kind of baking we do -- primarily bread.

PICS of my build

That deck is about 15 inches thick with reinforced concrete, vermicrete, concrete oven deck, sand, and fire brick. When it gets hot we can bake in it for two days.

[david s]

Re: Quantity of vermiculite per sq ft for v-crete?

It's been three years and numerous fires later -- still 130 degrees. My oven is off the ground with an ash dump below. There's plenty of room to work underneath and I had thought to add some insulation under the support slab -- maybe some 6 inch fiberglass batting. The oven actually works great. I've just got a bit more heat leakage than I'd like to have for the kind of baking we do -- primarily bread.

PICS of my build

That deck is about 15 inches thick with reinforced concrete, vermicrete, concrete oven deck, sand, and fire brick. When it gets hot we can bake in it for two days.

You'd think it would be dry after three years. I see you have a massive amount of thermal mass under the floor bricks, perhaps just a bit too much for the vermicrete to cope with adequately. You won't gain much by insulating under the supporting slab because the heat has already leaked into it. The drying of the vermicrete slab before building over it is quite important as the attachment demonstrates.

[lwalper]

Re: Quantity of vermiculite per sq ft for v-crete?

Yep, I think I'm dried out by now. The first fire was interesting. It may have been a couple of weeks since the last pour when I elected to light a little fire. Everything warmed up nicely -- fire out. Second fire a couple days later got a little bigger -- big enough to convert a lot of the retained water to steam which re-condensed as it escaped the oven confines. There was actually water running outside, down the side of the oven onto the ground. Pretty amazing! After cooling for a week or so I figured it was dry enough to thoroughly heat soak. I probably got a little carried away with temp of 1005?. I burn wood for winter heat and am familiar with how a heater behaves, but had never seen fire like that. That dude was hot.

Now we typically fire it to about 750? for flat breads, then with the falling heat in go the batards and boules right on the hearth, followed by ganged loaf pans when the hearth comes down to 425? or so. It takes a little planning for all the various breads needing different heats, but it works.