Vermiculite:Cement ratio

[lwalper]

Its been awhile since I built my oven so I don't remember the exact time frame from v-slab to first fire -- probably a month, but the second fire (quite a bit hotter than the first) caused water to FLOW out of the oven. It was a bit disconcerting to see water running out the side of the oven, but doesn't seem to have caused any harm.

[david s]

Your layer of bottles might actually work quite well, provided you have them packed tightly together so the vermicrete does not totally surround them. These air spaces can help move water and steam towards your drain holes, presuming you put some in. If I were in your situation i’d wait two weeks before laying the second layer of vermicrete. It is a bit like a pile of damp sand placed on a concrete slab. After a week the sand on the top will appear dry but the rest in the middle stays damp for months. Your slab will eventually dry but it will take months of fires to drive out all the water. Why not let nature do much of the drying for you now.

[UtahBeehiver]

Like I said yesterday in my response, at least two weeks, if you read David's white paper, he showed at three weeks 50% of the water still remained in the vcrete and that was a 2" slab............

[Monilee]

So I put some glass bottles on top of my concrete slab. Last night got half of my vcrete poured (6:1 ratio). Today I’ll finish the rest of the 7” vcrete pour. Then, any recommendations on how long until I start my floor bricks? And, also, should I put a thin course of sand down on top of the vcrete before laying the floor bricks?
Thanks all!

[david s]

Re: Vermiculite:Cement ratio

For those working with vermicrete, because it takes so much water there is way more than is required for the hydration process, so I never bother to cover it. The greater problem is trying to remove the water safely. It is easier to allow sun and wind to do much of this if the conditions are right and you can afford the time. See attached experiment.

[GrahamG]

Re: Vermiculite:Cement ratio

We created an enclosure around the dome, wrapped the dome in a 4" thick layer of fire blanket and filled the enclosure 6" above the dome with vermiculite.

The oven keeps hot until the following afternoon.

[cobblerdave]

Re: Vermiculite:Cement ratio

The finer grade is a bit easier to work, but requires more water which needs to be removed after it's set. I use a medium grade and have found a 50/50 mix of perlite and vermiculite makes a more workable mix than either alone, can't explain why. Also a little clay added helps make a more workable mix. I use about half a handful per litre of cement.

Gudday
Interesting point about adding clay to the mix, anything to make it easier to work with . A lot like fireclay in the "homebrew" mortar ?
I also understand how adding vermiculite would fill up the spaces in-between the spheres of pearlite.
Regards dave

[RichC]

Re: Vermiculite:Cement ratio

For the dome I had to increase the water quite a bit to make the vermicrete workable and stop it just crumbling away.

[david s]

Re: Vermiculite:Cement ratio

The finer grade is a bit easier to work, but requires more water which needs to be removed after it's set. I use a medium grade and have found a 50/50 mix of perlite and vermiculite makes a more workable mix than either alone, can't explain why. Also a little clay added helps make a more workable mix. I use about half a handful per litre of cement.

[cobblerdave]

Re: Vermiculite:Cement ratio

Gudday
You can get a good finish on V-Crete anyway by a combination of patting it down and smoothing it over with a steel float. A coat of cement paint and its waterproof. Sometimes we go a bit overkill in our constructions being DIYers.
Regards Dave

[UtahBeehiver]

Re: Vermiculite:Cement ratio

Stucco (render) over the vcrete.

[edjc]

Re: Vermiculite:Cement ratio

What do u mean by 'render'?

I will use Portland cement with the vermiculite.

Thinking of a ratio of about 5:1 , V:PC or 6-7:1

[UtahBeehiver]

Re: Vermiculite:Cement ratio

Ed,

A4 I believe is coarse grade used typically for packing. IHMO, it will work fine but you may have to make the cement/verm ratio richer to get good particle adhesion. Best way, try a couple small sample batches, ie 1 cement 5 verm. What are you going to render the insulation with?

[edjc]

Re: Vermiculite:Cement ratio

What type of vermiculite is recommended ( with cenent) for over dome as insulation ?

I gave the larger granular 'A4'

Ed

[Royal Ranger f16]

Re: Vermiculite:Cement ratio

I like the idea of a copper tube for the themocouple. Where do you want the themocouple to be located in the oven?