Sorry - another Vermiculite Question Pompeii Oven Construction Discuss Sorry - another Vermiculite Question in the Pizza Oven Design and Installation forums; When I did my vermiculite layer, I got worried because mine was very coarse and everyone was using fine grain ...

[Frances]

When I did my vermiculite layer, I got worried because mine was very coarse and everyone was using fine grain stuff... maybe its another of those things where it doesn't really matter much either way so long as you get the hydration and concrete proportion right?

[thebadger]

That's kind of my issue.

What I have is very fine - almost like sand. To be on the safe side I'll probably get the Isol board but still want to pour a smaller insulated hearth...

My main question is should the "fine" stuff be okay? 5 to 1 ratio as well?

Thanks
Dick

PS - George - I did see your response but want to get a consensus. This is something I can't change once my floor is down...

[gjbingham]

Otter,
You can't hurt my feelings. I would do the same! I thought you said you could take it back and exchange it?

[thebadger]

George,

Thanks!

I can - and I think I will take it back for the perlite... I'll probably put down a 3 1/2 inch layer (extra height and insulation) and then 2 inches of Iso board on top... That should bring my oven height to ~43".

Thanks
Dick

[gjbingham]

I like that! Lots of insulation under the floor. Great idea!

[thebadger]

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]

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]

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]

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]

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.