Pompeii Oven Insulation

[brickie in oz]

Re: Pompeii Oven Insulation

I could barely touch the dome it was so hot!

Its the moisture coming out, it should be cooler to touch when its dried out properly

[Neil2]

Re: Pompeii Oven Insulation

"vermiculite mixed with mortar"

Don't do this.

Mix the vermiculite (or perlite) with portland cement only. Mortar contains sands which will fill the pores, greatly reducing the insulation value.

"I could barely touch the dome it was so hot!"

As Al notes, this is common when curing or re-curing a dome. It is likely going to be steam build up. After several firings, the insulation layer will dry out and the outside should be cool to the touch. You can aid the drying out process by cutting a small (1 inch or so) vent through the mortar/render at the apex of the dome.

You need some patience at this stage. Try it for a while before ripping off the finish and adding insulation.

[sturoofer]

Re: Pompeii Oven Insulation

Thanks, yes I will have 6 or 7 fires to get it up to temp and then try cooking on it. It may be okay, but with only 1" of insulation I doubt it somehow. As I said though, should be fine for pizzas, espeically if there is some flame?
Thanks again
Stuart

[david s]

Re: Pompeii Oven Insulation

It is preferable to drive out the water before creating the outer shell, however as you've already done it just keep firing and it should dry out and perform much better. Moist insulation does not work too well and lots of it will just recondensing on the inside of the outer shell, but it will eventually find its way out and your oven should be then only warm to the touch on the outside, not hot.

[Bubazineti]

Re: Pompeii Oven Insulation

So i've had probably 10 fires now. Ended up doubling the chimney width and depth to about 6"x 8" iron rectangle and about 1m height which works a treat. Just sucks the smoke out.

When the firebricks are soaked there is a perceptible warmth over the top 2/3rds of the dome and warm to hot on the top behind the chimney and over the entrance.
For cooking a batch of pizzas, bread, cake it's fine. Everyone is full long before the temperature drops. However if I hadn't put so much fireclay over the insulation I would have added at least another inch of insulation or for the same money 4"of vermiculite for peace of mind. However the only person this bothers seems to be me.
Definitely steer clear of the Kaowool S and go for the Cerachem 1430 as It's noticeably cooler.

[PRPARKER]

Re: Pompeii Oven Insulation

A question for the team! I'll be insulating my dome very shortly. Is it possible to use the same perlite/cement mix which I used under the oven floor, say 3" thick? Rather than the blanket insulation? Many thanks to the Forum for lots of good information!

[Tscarborough]

Re: Pompeii Oven Insulation

Yes, although 4" would be better.

[PRPARKER]

Re: Pompeii Oven Insulation

On the dome for insulation, I plan to use 4" of perlite/cement mix applied to the exterior of the fire brick with 2" (+) of concrete (sakrete) on top of the perlite/cement mix. I thought I'd add a handful of "weep" holes (short pieces of galvanized conduit sloped down so as to not collect water, these weeps actually could be sealed at some time in the future) around the bottom perimeter of the dome to allow any moisture to escape from (allowing the system to breathe) the perlite/cement, etc. I'd appreciate any thoughts, comments or experiences!

[david s]

Re: Pompeii Oven Insulation

If you want to use perlcrete as your insulation do not go as rich as 5:1 because the cement reduces the insulation value. You only need enough to make it hold together.i find 10:1 works pretty well, but some members have used as low as 13:1. I have also found a mixture 50/50 of vermiculite, perlite works way better than either of them alone, I have no reason why. For any given volume of either perlite or vermiculite you need to add about a third of that volume in water to achieve the correct consistency. Also it is a good idea IMO to do the stuff in layers of around 1" and allow each layer around a week to dry because there is tons of water in a 4" layer of perlcrete to eliminate. I think your idea of little weep holes is a good one, because with such a thick layer of vermicrete the stuff can pick up a lot of moisture and after torrential rain and no oven use the recondensation of water inside the outer shell is considerable and it runs down the inside and gets quite wet around the base. A vent at the apex is also of benefit IMO. No amount of waterproofing the outside, apart from building an expensive roof, can prevent the vermiculite of perlite from picking up moisture.