Sorry - another Vermiculite Question

[thebadger]

Re: Sorry - another Vermiculite Question

Done,

Traded 4 bags of Vermiculite for Perlite.

Is the ration 5 to 1 or 6 to 1? My Pompeii version 1.2 says 5:1 but I see postings that say 6:1? Is it a big difference?

Thanks
Dick

[gjbingham]

Re: Sorry - another Vermiculite Question

Everyone chooses their own path. I did 5 to 1. 6 to 1 gives it higher insulative properties, at least I believe. I also believe that it makes it weaker due to the reduced amount of cement in the mix. People do what they think will be best in their own ovens. I followed the plans on that one.

[crowtrapper]

Re: Sorry - another Vermiculite Question

I used vermiculite for the outer insulation on the dome - 5:1 mix with cement, funny to work with really but it ended up OK. I put a rockwool blanket on the outside of the brick dome first, then alfoil, then about 3" of vermiculite/cement. The dome insulation appears to be very good - the hottest fire barely warms the outside. However, (too late to change it now), I used 3" AAC slabs under my hearth, and the floor of the oven cools off way quicker than the roof and walls. If I could do it again I would use a 5 or 6 inch layer of vermiculite under the hearth, because under that is a huge concrete slab heat sink. Not so good.
But -we pulled the first pizzas out last night - magical! Now we just need some cooler weather, around here it is about 40 degrees C each day and we are often not allowed to light fires at all!

[david s]

Re: Sorry - another Vermiculite Question

I think the 5:1 ratio is the go for the insulation under the oven floor because you need some strength there, but on the outside of the dome you only need sufficient cement to hold the stuff in place. A 5:1 ratio would mean far more weight in cement than vermiculite and reduces its insulation value enormously. I've found a 10:1 for the dome insulation is sufficient. Anyone else have ideas on this?

[crowtrapper]

Re: Sorry - another Vermiculite Question

The reason I used the 5:1 mix was that any weaker and the mix would not stick together at all. Maybe it depends on the particular texture of the vermiculite you have? It sounds as if it varies quite a bit.

[Bandrasco]

Re: Sorry - another Vermiculite Question

Sorry I didn't see your post earlier.

I used the fine vermiculite, 5:1, worked great. It took a week to really set up. It has worked out great so far, I don't have any probes in the floors or walls so I haven't been monitoring the temp drop but the oven holds temps that can cook for days. I used 4.5" of vermic/port on top of 4.5" concrete. The iso boards may work better though. In theory they would seem to have less of a heat sink property. On my dome I used 3" of Cerablanket by Thermal Dynamics, wire and vermicucrete at about an inch or so, then a waterproofing compound, stucco mix, then a layer of high grade exterior latex stucco paint (until I can get it covered with more brick). Absolutely zero heat transfer to the outer shell. Even after 4-5 hours of roaring fires.

Good luck.

[david s]

Re: Sorry - another Vermiculite Question

Yeah when you mix it up it is still loose and you think that it wont stick together, but it does, and when dry theres still plenty of air in it and not too much cement. Try it next time. For 10 L vermiculite add 1 L cement powder and 3 L water.